SYSTEMD.EXEC(5)



SYSTEMD.EXEC(5)                  systemd.exec                  SYSTEMD.EXEC(5)

NAME
       systemd.exec - Execution environment configuration

SYNOPSIS
       service.service, socket.socket, mount.mount, swap.swap

DESCRIPTION
       Unit configuration files for services, sockets, mount points, and swap
       devices share a subset of configuration options which define the
       execution environment of spawned processes.

       This man page lists the configuration options shared by these four unit
       types. See systemd.unit(5) for the common options of all unit
       configuration files, and systemd.service(5), systemd.socket(5),
       systemd.swap(5), and systemd.mount(5) for more information on the
       specific unit configuration files. The execution specific configuration
       options are configured in the [Service], [Socket], [Mount], or [Swap]
       sections, depending on the unit type.

       In addition, options which control resources through Linux Control
       Groups (cgroups) are listed in systemd.resource-control(5). Those
       options complement options listed here.

IMPLICIT DEPENDENCIES
       A few execution parameters result in additional, automatic dependencies
       to be added:

       o   Units with WorkingDirectory=, RootDirectory=, RootImage=,
           RuntimeDirectory=, StateDirectory=, CacheDirectory=, LogsDirectory=
           or ConfigurationDirectory= set automatically gain dependencies of
           type Requires= and After= on all mount units required to access the
           specified paths. This is equivalent to having them listed
           explicitly in RequiresMountsFor=.

       o   Similar, units with PrivateTmp= enabled automatically get mount
           unit dependencies for all mounts required to access /tmp and
           /var/tmp. They will also gain an automatic After= dependency on
           systemd-tmpfiles-setup.service(8).

       o   Units whose standard output or error output is connected to journal
           or kmsg (or their combinations with console output, see below)
           automatically acquire dependencies of type After= on
           systemd-journald.socket.

       o   Units using LogNamespace= will automatically gain ordering and
           requirement dependencies on the two socket units associated with
           systemd-journald@.service instances.

PATHS
       The following settings may be used to change a service's view of the
       filesystem. Please note that the paths must be absolute and must not
       contain a ".."  path component.

       WorkingDirectory=
           Takes a directory path relative to the service's root directory
           specified by RootDirectory=, or the special value "~". Sets the
           working directory for executed processes. If set to "~", the home
           directory of the user specified in User= is used. If not set,
           defaults to the root directory when systemd is running as a system
           instance and the respective user's home directory if run as user.
           If the setting is prefixed with the "-" character, a missing
           working directory is not considered fatal. If
           RootDirectory=/RootImage= is not set, then WorkingDirectory= is
           relative to the root of the system running the service manager.
           Note that setting this parameter might result in additional
           dependencies to be added to the unit (see above).

       RootDirectory=
           Takes a directory path relative to the host's root directory (i.e.
           the root of the system running the service manager). Sets the root
           directory for executed processes, with the chroot(2) system call.
           If this is used, it must be ensured that the process binary and all
           its auxiliary files are available in the chroot() jail. Note that
           setting this parameter might result in additional dependencies to
           be added to the unit (see above).

           The MountAPIVFS= and PrivateUsers= settings are particularly useful
           in conjunction with RootDirectory=. For details, see below.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       RootImage=
           Takes a path to a block device node or regular file as argument.
           This call is similar to RootDirectory= however mounts a file system
           hierarchy from a block device node or loopback file instead of a
           directory. The device node or file system image file needs to
           contain a file system without a partition table, or a file system
           within an MBR/MS-DOS or GPT partition table with only a single
           Linux-compatible partition, or a set of file systems within a GPT
           partition table that follows the Discoverable Partitions
           Specification[1].

           When DevicePolicy= is set to "closed" or "strict", or set to "auto"
           and DeviceAllow= is set, then this setting adds /dev/loop-control
           with rw mode, "block-loop" and "block-blkext" with rwm mode to
           DeviceAllow=. See systemd.resource-control(5) for the details about
           DevicePolicy= or DeviceAllow=. Also, see PrivateDevices= below, as
           it may change the setting of DevicePolicy=.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       MountAPIVFS=
           Takes a boolean argument. If on, a private mount namespace for the
           unit's processes is created and the API file systems /proc, /sys,
           and /dev are mounted inside of it, unless they are already mounted.
           Note that this option has no effect unless used in conjunction with
           RootDirectory=/RootImage= as these three mounts are generally
           mounted in the host anyway, and unless the root directory is
           changed, the private mount namespace will be a 1:1 copy of the
           host's, and include these three mounts. Note that the /dev file
           system of the host is bind mounted if this option is used without
           PrivateDevices=. To run the service with a private, minimal version
           of /dev/, combine this option with PrivateDevices=.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       BindPaths=, BindReadOnlyPaths=
           Configures unit-specific bind mounts. A bind mount makes a
           particular file or directory available at an additional place in
           the unit's view of the file system. Any bind mounts created with
           this option are specific to the unit, and are not visible in the
           host's mount table. This option expects a whitespace separated list
           of bind mount definitions. Each definition consists of a
           colon-separated triple of source path, destination path and option
           string, where the latter two are optional. If only a source path is
           specified the source and destination is taken to be the same. The
           option string may be either "rbind" or "norbind" for configuring a
           recursive or non-recursive bind mount. If the destination path is
           omitted, the option string must be omitted too. Each bind mount
           definition may be prefixed with "-", in which case it will be
           ignored when its source path does not exist.

           BindPaths= creates regular writable bind mounts (unless the source
           file system mount is already marked read-only), while
           BindReadOnlyPaths= creates read-only bind mounts. These settings
           may be used more than once, each usage appends to the unit's list
           of bind mounts. If the empty string is assigned to either of these
           two options the entire list of bind mounts defined prior to this is
           reset. Note that in this case both read-only and regular bind
           mounts are reset, regardless which of the two settings is used.

           This option is particularly useful when RootDirectory=/RootImage=
           is used. In this case the source path refers to a path on the host
           file system, while the destination path refers to a path below the
           root directory of the unit.

           Note that the destination directory must exist or systemd must be
           able to create it. Thus, it is not possible to use those options
           for mount points nested underneath paths specified in
           InaccessiblePaths=, or under /home/ and other protected directories
           if ProtectHome=yes is specified.  TemporaryFileSystem= with ":ro"
           or ProtectHome=tmpfs should be used instead.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

CREDENTIALS
       These options are only available for system services and are not
       supported for services running in per-user instances of the service
       manager.

       User=, Group=
           Set the UNIX user or group that the processes are executed as,
           respectively. Takes a single user or group name, or a numeric ID as
           argument. For system services (services run by the system service
           manager, i.e. managed by PID 1) and for user services of the root
           user (services managed by root's instance of systemd --user), the
           default is "root", but User= may be used to specify a different
           user. For user services of any other user, switching user identity
           is not permitted, hence the only valid setting is the same user the
           user's service manager is running as. If no group is set, the
           default group of the user is used. This setting does not affect
           commands whose command line is prefixed with "+".

           Note that this enforces only weak restrictions on the user/group
           name syntax, but will generate warnings in many cases where
           user/group names do not adhere to the following rules: the
           specified name should consist only of the characters a-z, A-Z, 0-9,
           "_" and "-", except for the first character which must be one of
           a-z, A-Z and "_" (i.e. digits and "-" are not permitted as first
           character). The user/group name must have at least one character,
           and at most 31. These restrictions are made in order to avoid
           ambiguities and to ensure user/group names and unit files remain
           portable among Linux systems. For further details on the names
           accepted and the names warned about see User/Group Name Syntax[2].

           When used in conjunction with DynamicUser= the user/group name
           specified is dynamically allocated at the time the service is
           started, and released at the time the service is stopped -- unless
           it is already allocated statically (see below). If DynamicUser= is
           not used the specified user and group must have been created
           statically in the user database no later than the moment the
           service is started, for example using the sysusers.d(5) facility,
           which is applied at boot or package install time. If the user does
           not exist by then program invocation will fail.

           If the User= setting is used the supplementary group list is
           initialized from the specified user's default group list, as
           defined in the system's user and group database. Additional groups
           may be configured through the SupplementaryGroups= setting (see
           below).

       DynamicUser=
           Takes a boolean parameter. If set, a UNIX user and group pair is
           allocated dynamically when the unit is started, and released as
           soon as it is stopped. The user and group will not be added to
           /etc/passwd or /etc/group, but are managed transiently during
           runtime. The nss-systemd(8) glibc NSS module provides integration
           of these dynamic users/groups into the system's user and group
           databases. The user and group name to use may be configured via
           User= and Group= (see above). If these options are not used and
           dynamic user/group allocation is enabled for a unit, the name of
           the dynamic user/group is implicitly derived from the unit name. If
           the unit name without the type suffix qualifies as valid user name
           it is used directly, otherwise a name incorporating a hash of it is
           used. If a statically allocated user or group of the configured
           name already exists, it is used and no dynamic user/group is
           allocated. Note that if User= is specified and the static group
           with the name exists, then it is required that the static user with
           the name already exists. Similarly, if Group= is specified and the
           static user with the name exists, then it is required that the
           static group with the name already exists. Dynamic users/groups are
           allocated from the UID/GID range 61184...65519. It is recommended
           to avoid this range for regular system or login users. At any point
           in time each UID/GID from this range is only assigned to zero or
           one dynamically allocated users/groups in use. However, UID/GIDs
           are recycled after a unit is terminated. Care should be taken that
           any processes running as part of a unit for which dynamic
           users/groups are enabled do not leave files or directories owned by
           these users/groups around, as a different unit might get the same
           UID/GID assigned later on, and thus gain access to these files or
           directories. If DynamicUser= is enabled, RemoveIPC= and PrivateTmp=
           are implied (and cannot be turned off). This ensures that the
           lifetime of IPC objects and temporary files created by the executed
           processes is bound to the runtime of the service, and hence the
           lifetime of the dynamic user/group. Since /tmp/ and /var/tmp/ are
           usually the only world-writable directories on a system this
           ensures that a unit making use of dynamic user/group allocation
           cannot leave files around after unit termination. Furthermore
           NoNewPrivileges= and RestrictSUIDSGID= are implicitly enabled (and
           cannot be disabled), to ensure that processes invoked cannot take
           benefit or create SUID/SGID files or directories. Moreover
           ProtectSystem=strict and ProtectHome=read-only are implied, thus
           prohibiting the service to write to arbitrary file system
           locations. In order to allow the service to write to certain
           directories, they have to be whitelisted using ReadWritePaths=, but
           care must be taken so that UID/GID recycling doesn't create
           security issues involving files created by the service. Use
           RuntimeDirectory= (see below) in order to assign a writable runtime
           directory to a service, owned by the dynamic user/group and removed
           automatically when the unit is terminated. Use StateDirectory=,
           CacheDirectory= and LogsDirectory= in order to assign a set of
           writable directories for specific purposes to the service in a way
           that they are protected from vulnerabilities due to UID reuse (see
           below). If this option is enabled, care should be taken that the
           unit's processes do not get access to directories outside of these
           explicitly configured and managed ones. Specifically, do not use
           BindPaths= and be careful with AF_UNIX file descriptor passing for
           directory file descriptors, as this would permit processes to
           create files or directories owned by the dynamic user/group that
           are not subject to the lifecycle and access guarantees of the
           service. Defaults to off.

       SupplementaryGroups=
           Sets the supplementary Unix groups the processes are executed as.
           This takes a space-separated list of group names or IDs. This
           option may be specified more than once, in which case all listed
           groups are set as supplementary groups. When the empty string is
           assigned, the list of supplementary groups is reset, and all
           assignments prior to this one will have no effect. In any way, this
           option does not override, but extends the list of supplementary
           groups configured in the system group database for the user. This
           does not affect commands prefixed with "+".

       PAMName=
           Sets the PAM service name to set up a session as. If set, the
           executed process will be registered as a PAM session under the
           specified service name. This is only useful in conjunction with the
           User= setting, and is otherwise ignored. If not set, no PAM session
           will be opened for the executed processes. See pam(8) for details.

           Note that for each unit making use of this option a PAM session
           handler process will be maintained as part of the unit and stays
           around as long as the unit is active, to ensure that appropriate
           actions can be taken when the unit and hence the PAM session
           terminates. This process is named "(sd-pam)" and is an immediate
           child process of the unit's main process.

           Note that when this option is used for a unit it is very likely
           (depending on PAM configuration) that the main unit process will be
           migrated to its own session scope unit when it is activated. This
           process will hence be associated with two units: the unit it was
           originally started from (and for which PAMName= was configured),
           and the session scope unit. Any child processes of that process
           will however be associated with the session scope unit only. This
           has implications when used in combination with NotifyAccess=all, as
           these child processes will not be able to affect changes in the
           original unit through notification messages. These messages will be
           considered belonging to the session scope unit and not the original
           unit. It is hence not recommended to use PAMName= in combination
           with NotifyAccess=all.

CAPABILITIES
       These options are only available for system services and are not
       supported for services running in per-user instances of the service
       manager.

       CapabilityBoundingSet=
           Controls which capabilities to include in the capability bounding
           set for the executed process. See capabilities(7) for details.
           Takes a whitespace-separated list of capability names, e.g.
           CAP_SYS_ADMIN, CAP_DAC_OVERRIDE, CAP_SYS_PTRACE. Capabilities
           listed will be included in the bounding set, all others are
           removed. If the list of capabilities is prefixed with "~", all but
           the listed capabilities will be included, the effect of the
           assignment inverted. Note that this option also affects the
           respective capabilities in the effective, permitted and inheritable
           capability sets. If this option is not used, the capability
           bounding set is not modified on process execution, hence no limits
           on the capabilities of the process are enforced. This option may
           appear more than once, in which case the bounding sets are merged
           by OR, or by AND if the lines are prefixed with "~" (see below). If
           the empty string is assigned to this option, the bounding set is
           reset to the empty capability set, and all prior settings have no
           effect. If set to "~" (without any further argument), the bounding
           set is reset to the full set of available capabilities, also
           undoing any previous settings. This does not affect commands
           prefixed with "+".

           Example: if a unit has the following,

               CapabilityBoundingSet=CAP_A CAP_B
               CapabilityBoundingSet=CAP_B CAP_C

           then CAP_A, CAP_B, and CAP_C are set. If the second line is
           prefixed with "~", e.g.,

               CapabilityBoundingSet=CAP_A CAP_B
               CapabilityBoundingSet=~CAP_B CAP_C

           then, only CAP_A is set.

       AmbientCapabilities=
           Controls which capabilities to include in the ambient capability
           set for the executed process. Takes a whitespace-separated list of
           capability names, e.g.  CAP_SYS_ADMIN, CAP_DAC_OVERRIDE,
           CAP_SYS_PTRACE. This option may appear more than once in which case
           the ambient capability sets are merged (see the above examples in
           CapabilityBoundingSet=). If the list of capabilities is prefixed
           with "~", all but the listed capabilities will be included, the
           effect of the assignment inverted. If the empty string is assigned
           to this option, the ambient capability set is reset to the empty
           capability set, and all prior settings have no effect. If set to
           "~" (without any further argument), the ambient capability set is
           reset to the full set of available capabilities, also undoing any
           previous settings. Note that adding capabilities to ambient
           capability set adds them to the process's inherited capability set.

           Ambient capability sets are useful if you want to execute a process
           as a non-privileged user but still want to give it some
           capabilities. Note that in this case option keep-caps is
           automatically added to SecureBits= to retain the capabilities over
           the user change.  AmbientCapabilities= does not affect commands
           prefixed with "+".

SECURITY
       NoNewPrivileges=
           Takes a boolean argument. If true, ensures that the service process
           and all its children can never gain new privileges through execve()
           (e.g. via setuid or setgid bits, or filesystem capabilities). This
           is the simplest and most effective way to ensure that a process and
           its children can never elevate privileges again. Defaults to false,
           but certain settings override this and ignore the value of this
           setting. This is the case when SystemCallFilter=,
           SystemCallArchitectures=, RestrictAddressFamilies=,
           RestrictNamespaces=, PrivateDevices=, ProtectKernelTunables=,
           ProtectKernelModules=, ProtectKernelLogs=, ProtectClock=,
           MemoryDenyWriteExecute=, RestrictRealtime=, RestrictSUIDSGID=,
           DynamicUser= or LockPersonality= are specified. Note that even if
           this setting is overridden by them, systemctl show shows the
           original value of this setting. Also see No New Privileges Flag[3].

       SecureBits=
           Controls the secure bits set for the executed process. Takes a
           space-separated combination of options from the following list:
           keep-caps, keep-caps-locked, no-setuid-fixup,
           no-setuid-fixup-locked, noroot, and noroot-locked. This option may
           appear more than once, in which case the secure bits are ORed. If
           the empty string is assigned to this option, the bits are reset to
           0. This does not affect commands prefixed with "+". See
           capabilities(7) for details.

MANDATORY ACCESS CONTROL
       These options are only available for system services and are not
       supported for services running in per-user instances of the service
       manager.

       SELinuxContext=
           Set the SELinux security context of the executed process. If set,
           this will override the automated domain transition. However, the
           policy still needs to authorize the transition. This directive is
           ignored if SELinux is disabled. If prefixed by "-", all errors will
           be ignored. This does not affect commands prefixed with "+". See
           setexeccon(3) for details.

       AppArmorProfile=
           Takes a profile name as argument. The process executed by the unit
           will switch to this profile when started. Profiles must already be
           loaded in the kernel, or the unit will fail. This result in a non
           operation if AppArmor is not enabled. If prefixed by "-", all
           errors will be ignored. This does not affect commands prefixed with
           "+".

       SmackProcessLabel=
           Takes a SMACK64 security label as argument. The process executed by
           the unit will be started under this label and SMACK will decide
           whether the process is allowed to run or not, based on it. The
           process will continue to run under the label specified here unless
           the executable has its own SMACK64EXEC label, in which case the
           process will transition to run under that label. When not
           specified, the label that systemd is running under is used. This
           directive is ignored if SMACK is disabled.

           The value may be prefixed by "-", in which case all errors will be
           ignored. An empty value may be specified to unset previous
           assignments. This does not affect commands prefixed with "+".

PROCESS PROPERTIES
       LimitCPU=, LimitFSIZE=, LimitDATA=, LimitSTACK=, LimitCORE=, LimitRSS=,
       LimitNOFILE=, LimitAS=, LimitNPROC=, LimitMEMLOCK=, LimitLOCKS=,
       LimitSIGPENDING=, LimitMSGQUEUE=, LimitNICE=, LimitRTPRIO=,
       LimitRTTIME=
           Set soft and hard limits on various resources for executed
           processes. See setrlimit(2) for details on the resource limit
           concept. Resource limits may be specified in two formats: either as
           single value to set a specific soft and hard limit to the same
           value, or as colon-separated pair soft:hard to set both limits
           individually (e.g.  "LimitAS=4G:16G"). Use the string infinity to
           configure no limit on a specific resource. The multiplicative
           suffixes K, M, G, T, P and E (to the base 1024) may be used for
           resource limits measured in bytes (e.g.  "LimitAS=16G"). For the
           limits referring to time values, the usual time units ms, s, min, h
           and so on may be used (see systemd.time(7) for details). Note that
           if no time unit is specified for LimitCPU= the default unit of
           seconds is implied, while for LimitRTTIME= the default unit of
           microseconds is implied. Also, note that the effective granularity
           of the limits might influence their enforcement. For example, time
           limits specified for LimitCPU= will be rounded up implicitly to
           multiples of 1s. For LimitNICE= the value may be specified in two
           syntaxes: if prefixed with "+" or "-", the value is understood as
           regular Linux nice value in the range -20..19. If not prefixed like
           this the value is understood as raw resource limit parameter in the
           range 0..40 (with 0 being equivalent to 1).

           Note that most process resource limits configured with these
           options are per-process, and processes may fork in order to acquire
           a new set of resources that are accounted independently of the
           original process, and may thus escape limits set. Also note that
           LimitRSS= is not implemented on Linux, and setting it has no
           effect. Often it is advisable to prefer the resource controls
           listed in systemd.resource-control(5) over these per-process
           limits, as they apply to services as a whole, may be altered
           dynamically at runtime, and are generally more expressive. For
           example, MemoryMax= is a more powerful (and working) replacement
           for LimitRSS=.

           Resource limits not configured explicitly for a unit default to the
           value configured in the various DefaultLimitCPU=,
           DefaultLimitFSIZE=, ... options available in systemd-
           system.conf(5), and - if not configured there - the kernel or
           per-user defaults, as defined by the OS (the latter only for user
           services, see below).

           For system units these resource limits may be chosen freely. When
           these settings are configured in a user service (i.e. a service run
           by the per-user instance of the service manager) they cannot be
           used to raise the limits above those set for the user manager
           itself when it was first invoked, as the user's service manager
           generally lacks the privileges to do so. In user context these
           configuration options are hence only useful to lower the limits
           passed in or to raise the soft limit to the maximum of the hard
           limit as configured for the user. To raise the user's limits
           further, the available configuration mechanisms differ between
           operating systems, but typically require privileges. In most cases
           it is possible to configure higher per-user resource limits via PAM
           or by setting limits on the system service encapsulating the user's
           service manager, i.e. the user's instance of user@.service. After
           making such changes, make sure to restart the user's service
           manager.

           Table 1. Resource limit directives, their equivalent ulimit shell
           commands and the unit used
           +-----------------+-------------------+---------------------+
           |Directive        | ulimit equivalent | Unit                |
           +-----------------+-------------------+---------------------+
           |LimitCPU=        | ulimit -t         | Seconds             |
           +-----------------+-------------------+---------------------+
           |LimitFSIZE=      | ulimit -f         | Bytes               |
           +-----------------+-------------------+---------------------+
           |LimitDATA=       | ulimit -d         | Bytes               |
           +-----------------+-------------------+---------------------+
           |LimitSTACK=      | ulimit -s         | Bytes               |
           +-----------------+-------------------+---------------------+
           |LimitCORE=       | ulimit -c         | Bytes               |
           +-----------------+-------------------+---------------------+
           |LimitRSS=        | ulimit -m         | Bytes               |
           +-----------------+-------------------+---------------------+
           |LimitNOFILE=     | ulimit -n         | Number of File      |
           |                 |                   | Descriptors         |
           +-----------------+-------------------+---------------------+
           |LimitAS=         | ulimit -v         | Bytes               |
           +-----------------+-------------------+---------------------+
           |LimitNPROC=      | ulimit -u         | Number of Processes |
           +-----------------+-------------------+---------------------+
           |LimitMEMLOCK=    | ulimit -l         | Bytes               |
           +-----------------+-------------------+---------------------+
           |LimitLOCKS=      | ulimit -x         | Number of Locks     |
           +-----------------+-------------------+---------------------+
           |LimitSIGPENDING= | ulimit -i         | Number of Queued    |
           |                 |                   | Signals             |
           +-----------------+-------------------+---------------------+
           |LimitMSGQUEUE=   | ulimit -q         | Bytes               |
           +-----------------+-------------------+---------------------+
           |LimitNICE=       | ulimit -e         | Nice Level          |
           +-----------------+-------------------+---------------------+
           |LimitRTPRIO=     | ulimit -r         | Realtime Priority   |
           +-----------------+-------------------+---------------------+
           |LimitRTTIME=     | No equivalent     | Microseconds        |
           +-----------------+-------------------+---------------------+

       UMask=
           Controls the file mode creation mask. Takes an access mode in octal
           notation. See umask(2) for details. Defaults to 0022 for system
           units. For units of the user service manager the default value is
           inherited from the user instance (whose default is inherited from
           the system service manager, and thus also is 0022). Hence changing
           the default value of a user instance, either via UMask= or via a
           PAM module, will affect the user instance itself and all user units
           started by the user instance unless a user unit has specified its
           own UMask=.

       KeyringMode=
           Controls how the kernel session keyring is set up for the service
           (see session-keyring(7) for details on the session keyring). Takes
           one of inherit, private, shared. If set to inherit no special
           keyring setup is done, and the kernel's default behaviour is
           applied. If private is used a new session keyring is allocated when
           a service process is invoked, and it is not linked up with any user
           keyring. This is the recommended setting for system services, as
           this ensures that multiple services running under the same system
           user ID (in particular the root user) do not share their key
           material among each other. If shared is used a new session keyring
           is allocated as for private, but the user keyring of the user
           configured with User= is linked into it, so that keys assigned to
           the user may be requested by the unit's processes. In this modes
           multiple units running processes under the same user ID may share
           key material. Unless inherit is selected the unique invocation ID
           for the unit (see below) is added as a protected key by the name
           "invocation_id" to the newly created session keyring. Defaults to
           private for services of the system service manager and to inherit
           for non-service units and for services of the user service manager.

       OOMScoreAdjust=
           Sets the adjustment value for the Linux kernel's Out-Of-Memory
           (OOM) killer score for executed processes. Takes an integer between
           -1000 (to disable OOM killing of processes of this unit) and 1000
           (to make killing of processes of this unit under memory pressure
           very likely). See proc.txt[4] for details. If not specified
           defaults to the OOM score adjustment level of the service manager
           itself, which is normally at 0.

           Use the OOMPolicy= setting of service units to configure how the
           service manager shall react to the kernel OOM killer terminating a
           process of the service. See systemd.service(5) for details.

       TimerSlackNSec=
           Sets the timer slack in nanoseconds for the executed processes. The
           timer slack controls the accuracy of wake-ups triggered by timers.
           See prctl(2) for more information. Note that in contrast to most
           other time span definitions this parameter takes an integer value
           in nano-seconds if no unit is specified. The usual time units are
           understood too.

       Personality=
           Controls which kernel architecture uname(2) shall report, when
           invoked by unit processes. Takes one of the architecture
           identifiers x86, x86-64, ppc, ppc-le, ppc64, ppc64-le, s390 or
           s390x. Which personality architectures are supported depends on the
           system architecture. Usually the 64bit versions of the various
           system architectures support their immediate 32bit personality
           architecture counterpart, but no others. For example, x86-64
           systems support the x86-64 and x86 personalities but no others. The
           personality feature is useful when running 32-bit services on a
           64-bit host system. If not specified, the personality is left
           unmodified and thus reflects the personality of the host system's
           kernel.

       IgnoreSIGPIPE=
           Takes a boolean argument. If true, causes SIGPIPE to be ignored in
           the executed process. Defaults to true because SIGPIPE generally is
           useful only in shell pipelines.

SCHEDULING
       Nice=
           Sets the default nice level (scheduling priority) for executed
           processes. Takes an integer between -20 (highest priority) and 19
           (lowest priority). See setpriority(2) for details.

       CPUSchedulingPolicy=
           Sets the CPU scheduling policy for executed processes. Takes one of
           other, batch, idle, fifo or rr. See sched_setscheduler(2) for
           details.

       CPUSchedulingPriority=
           Sets the CPU scheduling priority for executed processes. The
           available priority range depends on the selected CPU scheduling
           policy (see above). For real-time scheduling policies an integer
           between 1 (lowest priority) and 99 (highest priority) can be used.
           See sched_setscheduler(2) for details.

       CPUSchedulingResetOnFork=
           Takes a boolean argument. If true, elevated CPU scheduling
           priorities and policies will be reset when the executed processes
           fork, and can hence not leak into child processes. See
           sched_setscheduler(2) for details. Defaults to false.

       CPUAffinity=
           Controls the CPU affinity of the executed processes. Takes a list
           of CPU indices or ranges separated by either whitespace or commas.
           Alternatively, takes a special "numa" value in which case systemd
           automatically derives allowed CPU range based on the value of
           NUMAMask= option. CPU ranges are specified by the lower and upper
           CPU indices separated by a dash. This option may be specified more
           than once, in which case the specified CPU affinity masks are
           merged. If the empty string is assigned, the mask is reset, all
           assignments prior to this will have no effect. See
           sched_setaffinity(2) for details.

       NUMAPolicy=
           Controls the NUMA memory policy of the executed processes. Takes a
           policy type, one of: default, preferred, bind, interleave and
           local. A list of NUMA nodes that should be associated with the
           policy must be specified in NUMAMask=. For more details on each
           policy please see, set_mempolicy(2). For overall overview of NUMA
           support in Linux see, numa(7)

       NUMAMask=
           Controls the NUMA node list which will be applied alongside with
           selected NUMA policy. Takes a list of NUMA nodes and has the same
           syntax as a list of CPUs for CPUAffinity= option. Note that the
           list of NUMA nodes is not required for default and local policies
           and for preferred policy we expect a single NUMA node.

       IOSchedulingClass=
           Sets the I/O scheduling class for executed processes. Takes an
           integer between 0 and 3 or one of the strings none, realtime,
           best-effort or idle. If the empty string is assigned to this
           option, all prior assignments to both IOSchedulingClass= and
           IOSchedulingPriority= have no effect. See ioprio_set(2) for
           details.

       IOSchedulingPriority=
           Sets the I/O scheduling priority for executed processes. Takes an
           integer between 0 (highest priority) and 7 (lowest priority). The
           available priorities depend on the selected I/O scheduling class
           (see above). If the empty string is assigned to this option, all
           prior assignments to both IOSchedulingClass= and
           IOSchedulingPriority= have no effect. See ioprio_set(2) for
           details.

SANDBOXING
       The following sandboxing options are an effective way to limit the
       exposure of the system towards the unit's processes. It is recommended
       to turn on as many of these options for each unit as is possible
       without negatively affecting the process' ability to operate. Note that
       many of these sandboxing features are gracefully turned off on systems
       where the underlying security mechanism is not available. For example,
       ProtectSystem= has no effect if the kernel is built without file system
       namespacing or if the service manager runs in a container manager that
       makes file system namespacing unavailable to its payload. Similar,
       RestrictRealtime= has no effect on systems that lack support for
       SECCOMP system call filtering, or in containers where support for this
       is turned off.

       Also note that some sandboxing functionality is generally not available
       in user services (i.e. services run by the per-user service manager).
       Specifically, the various settings requiring file system namespacing
       support (such as ProtectSystem=) are not available, as the underlying
       kernel functionality is only accessible to privileged processes.
       However, most namespacing settings, that will not work on their own in
       user services, will work when used in conjunction with
       PrivateUsers=true.

       ProtectSystem=
           Takes a boolean argument or the special values "full" or "strict".
           If true, mounts the /usr and the boot loader directories (/boot and
           /efi) read-only for processes invoked by this unit. If set to
           "full", the /etc directory is mounted read-only, too. If set to
           "strict" the entire file system hierarchy is mounted read-only,
           except for the API file system subtrees /dev, /proc and /sys
           (protect these directories using PrivateDevices=,
           ProtectKernelTunables=, ProtectControlGroups=). This setting
           ensures that any modification of the vendor-supplied operating
           system (and optionally its configuration, and local mounts) is
           prohibited for the service. It is recommended to enable this
           setting for all long-running services, unless they are involved
           with system updates or need to modify the operating system in other
           ways. If this option is used, ReadWritePaths= may be used to
           exclude specific directories from being made read-only. This
           setting is implied if DynamicUser= is set. This setting cannot
           ensure protection in all cases. In general it has the same
           limitations as ReadOnlyPaths=, see below. Defaults to off.

       ProtectHome=
           Takes a boolean argument or the special values "read-only" or
           "tmpfs". If true, the directories /home, /root, and /run/user are
           made inaccessible and empty for processes invoked by this unit. If
           set to "read-only", the three directories are made read-only
           instead. If set to "tmpfs", temporary file systems are mounted on
           the three directories in read-only mode. The value "tmpfs" is
           useful to hide home directories not relevant to the processes
           invoked by the unit, while still allowing necessary directories to
           be made visible when listed in BindPaths= or BindReadOnlyPaths=.

           Setting this to "yes" is mostly equivalent to set the three
           directories in InaccessiblePaths=. Similarly, "read-only" is mostly
           equivalent to ReadOnlyPaths=, and "tmpfs" is mostly equivalent to
           TemporaryFileSystem= with ":ro".

           It is recommended to enable this setting for all long-running
           services (in particular network-facing ones), to ensure they cannot
           get access to private user data, unless the services actually
           require access to the user's private data. This setting is implied
           if DynamicUser= is set. This setting cannot ensure protection in
           all cases. In general it has the same limitations as
           ReadOnlyPaths=, see below.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       RuntimeDirectory=, StateDirectory=, CacheDirectory=, LogsDirectory=,
       ConfigurationDirectory=
           These options take a whitespace-separated list of directory names.
           The specified directory names must be relative, and may not include
           "..". If set, one or more directories by the specified names will
           be created (including their parents) below the locations defined in
           the following table, when the unit is started. Also, the
           corresponding environment variable is defined with the full path of
           directories. If multiple directories are set, then in the
           environment variable the paths are concatenated with colon (":").

           Table 2. Automatic directory creation and environment variables
           +------------------------+----------------+-----------------------+--------------------------+
           |Directory               | Below path for | Below path for        | Environment              |
           |                        | system units   | user units            | variable set             |
           +------------------------+----------------+-----------------------+--------------------------+
           |RuntimeDirectory=       | /run/          | $XDG_RUNTIME_DIR      | $RUNTIME_DIRECTORY       |
           +------------------------+----------------+-----------------------+--------------------------+
           |StateDirectory=         | /var/lib/      | $XDG_CONFIG_HOME      | $STATE_DIRECTORY         |
           +------------------------+----------------+-----------------------+--------------------------+
           |CacheDirectory=         | /var/cache/    | $XDG_CACHE_HOME       | $CACHE_DIRECTORY         |
           +------------------------+----------------+-----------------------+--------------------------+
           |LogsDirectory=          | /var/log/      | $XDG_CONFIG_HOME/log/ | $LOGS_DIRECTORY          |
           +------------------------+----------------+-----------------------+--------------------------+
           |ConfigurationDirectory= | /etc/          | $XDG_CONFIG_HOME      | $CONFIGURATION_DIRECTORY |
           +------------------------+----------------+-----------------------+--------------------------+
           In case of RuntimeDirectory= the innermost subdirectories are
           removed when the unit is stopped. It is possible to preserve the
           specified directories in this case if RuntimeDirectoryPreserve= is
           configured to restart or yes (see below). The directories specified
           with StateDirectory=, CacheDirectory=, LogsDirectory=,
           ConfigurationDirectory= are not removed when the unit is stopped.

           Except in case of ConfigurationDirectory=, the innermost specified
           directories will be owned by the user and group specified in User=
           and Group=. If the specified directories already exist and their
           owning user or group do not match the configured ones, all files
           and directories below the specified directories as well as the
           directories themselves will have their file ownership recursively
           changed to match what is configured. As an optimization, if the
           specified directories are already owned by the right user and
           group, files and directories below of them are left as-is, even if
           they do not match what is requested. The innermost specified
           directories will have their access mode adjusted to the what is
           specified in RuntimeDirectoryMode=, StateDirectoryMode=,
           CacheDirectoryMode=, LogsDirectoryMode= and
           ConfigurationDirectoryMode=.

           These options imply BindPaths= for the specified paths. When
           combined with RootDirectory= or RootImage= these paths always
           reside on the host and are mounted from there into the unit's file
           system namespace.

           If DynamicUser= is used in conjunction with StateDirectory=,
           CacheDirectory= and LogsDirectory= is slightly altered: the
           directories are created below /var/lib/private, /var/cache/private
           and /var/log/private, respectively, which are host directories made
           inaccessible to unprivileged users, which ensures that access to
           these directories cannot be gained through dynamic user ID
           recycling. Symbolic links are created to hide this difference in
           behaviour. Both from perspective of the host and from inside the
           unit, the relevant directories hence always appear directly below
           /var/lib, /var/cache and /var/log.

           Use RuntimeDirectory= to manage one or more runtime directories for
           the unit and bind their lifetime to the daemon runtime. This is
           particularly useful for unprivileged daemons that cannot create
           runtime directories in /run due to lack of privileges, and to make
           sure the runtime directory is cleaned up automatically after use.
           For runtime directories that require more complex or different
           configuration or lifetime guarantees, please consider using
           tmpfiles.d(5).

           The directories defined by these options are always created under
           the standard paths used by systemd (/var, /run, /etc, ...). If the
           service needs directories in a different location, a different
           mechanism has to be used to create them.

           tmpfiles.d(5) provides functionality that overlaps with these
           options. Using these options is recommended, because the lifetime
           of the directories is tied directly to the lifetime of the unit,
           and it is not necessary to ensure that the tmpfiles.d configuration
           is executed before the unit is started.

           To remove any of the directories created by these settings, use the
           systemctl clean ...  command on the relevant units, see
           systemctl(1) for details.

           Example: if a system service unit has the following,

               RuntimeDirectory=foo/bar baz

           the service manager creates /run/foo (if it does not exist),
           /run/foo/bar, and /run/baz. The directories /run/foo/bar and
           /run/baz except /run/foo are owned by the user and group specified
           in User= and Group=, and removed when the service is stopped.

           Example: if a system service unit has the following,

               RuntimeDirectory=foo/bar
               StateDirectory=aaa/bbb ccc

           then the environment variable "RUNTIME_DIRECTORY" is set with
           "/run/foo/bar", and "STATE_DIRECTORY" is set with
           "/var/lib/aaa/bbb:/var/lib/ccc".

       RuntimeDirectoryMode=, StateDirectoryMode=, CacheDirectoryMode=,
       LogsDirectoryMode=, ConfigurationDirectoryMode=
           Specifies the access mode of the directories specified in
           RuntimeDirectory=, StateDirectory=, CacheDirectory=,
           LogsDirectory=, or ConfigurationDirectory=, respectively, as an
           octal number. Defaults to 0755. See "Permissions" in
           path_resolution(7) for a discussion of the meaning of permission
           bits.

       RuntimeDirectoryPreserve=
           Takes a boolean argument or restart. If set to no (the default),
           the directories specified in RuntimeDirectory= are always removed
           when the service stops. If set to restart the directories are
           preserved when the service is both automatically and manually
           restarted. Here, the automatic restart means the operation
           specified in Restart=, and manual restart means the one triggered
           by systemctl restart foo.service. If set to yes, then the
           directories are not removed when the service is stopped. Note that
           since the runtime directory /run is a mount point of "tmpfs", then
           for system services the directories specified in RuntimeDirectory=
           are removed when the system is rebooted.

       TimeoutCleanSec=
           Configures a timeout on the clean-up operation requested through
           systemctl clean ..., see systemctl(1) for details. Takes the usual
           time values and defaults to infinity, i.e. by default no time-out
           is applied. If a time-out is configured the clean operation will be
           aborted forcibly when the time-out is reached, potentially leaving
           resources on disk.

       ReadWritePaths=, ReadOnlyPaths=, InaccessiblePaths=
           Sets up a new file system namespace for executed processes. These
           options may be used to limit access a process might have to the
           file system hierarchy. Each setting takes a space-separated list of
           paths relative to the host's root directory (i.e. the system
           running the service manager). Note that if paths contain symlinks,
           they are resolved relative to the root directory set with
           RootDirectory=/RootImage=.

           Paths listed in ReadWritePaths= are accessible from within the
           namespace with the same access modes as from outside of it. Paths
           listed in ReadOnlyPaths= are accessible for reading only, writing
           will be refused even if the usual file access controls would permit
           this. Nest ReadWritePaths= inside of ReadOnlyPaths= in order to
           provide writable subdirectories within read-only directories. Use
           ReadWritePaths= in order to whitelist specific paths for write
           access if ProtectSystem=strict is used.

           Paths listed in InaccessiblePaths= will be made inaccessible for
           processes inside the namespace along with everything below them in
           the file system hierarchy. This may be more restrictive than
           desired, because it is not possible to nest ReadWritePaths=,
           ReadOnlyPaths=, BindPaths=, or BindReadOnlyPaths= inside it. For a
           more flexible option, see TemporaryFileSystem=.

           Non-directory paths may be specified as well. These options may be
           specified more than once, in which case all paths listed will have
           limited access from within the namespace. If the empty string is
           assigned to this option, the specific list is reset, and all prior
           assignments have no effect.

           Paths in ReadWritePaths=, ReadOnlyPaths= and InaccessiblePaths= may
           be prefixed with "-", in which case they will be ignored when they
           do not exist. If prefixed with "+" the paths are taken relative to
           the root directory of the unit, as configured with
           RootDirectory=/RootImage=, instead of relative to the root
           directory of the host (see above). When combining "-" and "+" on
           the same path make sure to specify "-" first, and "+" second.

           Note that these settings will disconnect propagation of mounts from
           the unit's processes to the host. This means that this setting may
           not be used for services which shall be able to install mount
           points in the main mount namespace. For ReadWritePaths= and
           ReadOnlyPaths= propagation in the other direction is not affected,
           i.e. mounts created on the host generally appear in the unit
           processes' namespace, and mounts removed on the host also disappear
           there too. In particular, note that mount propagation from host to
           unit will result in unmodified mounts to be created in the unit's
           namespace, i.e. writable mounts appearing on the host will be
           writable in the unit's namespace too, even when propagated below a
           path marked with ReadOnlyPaths=! Restricting access with these
           options hence does not extend to submounts of a directory that are
           created later on. This means the lock-down offered by that setting
           is not complete, and does not offer full protection.

           Note that the effect of these settings may be undone by privileged
           processes. In order to set up an effective sandboxed environment
           for a unit it is thus recommended to combine these settings with
           either CapabilityBoundingSet=~CAP_SYS_ADMIN or
           SystemCallFilter=~@mount.

           These options are only available for system services and are not
           supported for services running in per-user instances of the service
           manager.

       TemporaryFileSystem=
           Takes a space-separated list of mount points for temporary file
           systems (tmpfs). If set, a new file system namespace is set up for
           executed processes, and a temporary file system is mounted on each
           mount point. This option may be specified more than once, in which
           case temporary file systems are mounted on all listed mount points.
           If the empty string is assigned to this option, the list is reset,
           and all prior assignments have no effect. Each mount point may
           optionally be suffixed with a colon (":") and mount options such as
           "size=10%" or "ro". By default, each temporary file system is
           mounted with "nodev,strictatime,mode=0755". These can be disabled
           by explicitly specifying the corresponding mount options, e.g.,
           "dev" or "nostrictatime".

           This is useful to hide files or directories not relevant to the
           processes invoked by the unit, while necessary files or directories
           can be still accessed by combining with BindPaths= or
           BindReadOnlyPaths=:

           Example: if a unit has the following,

               TemporaryFileSystem=/var:ro
               BindReadOnlyPaths=/var/lib/systemd

           then the invoked processes by the unit cannot see any files or
           directories under /var except for /var/lib/systemd or its contents.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       PrivateTmp=
           Takes a boolean argument. If true, sets up a new file system
           namespace for the executed processes and mounts private /tmp and
           /var/tmp directories inside it that is not shared by processes
           outside of the namespace. This is useful to secure access to
           temporary files of the process, but makes sharing between processes
           via /tmp or /var/tmp impossible. If this is enabled, all temporary
           files created by a service in these directories will be removed
           after the service is stopped. Defaults to false. It is possible to
           run two or more units within the same private /tmp and /var/tmp
           namespace by using the JoinsNamespaceOf= directive, see
           systemd.unit(5) for details. This setting is implied if
           DynamicUser= is set. For this setting the same restrictions
           regarding mount propagation and privileges apply as for
           ReadOnlyPaths= and related calls, see above. Enabling this setting
           has the side effect of adding Requires= and After= dependencies on
           all mount units necessary to access /tmp and /var/tmp. Moreover an
           implicitly After= ordering on systemd-tmpfiles-setup.service(8) is
           added.

           Note that the implementation of this setting might be impossible
           (for example if mount namespaces are not available), and the unit
           should be written in a way that does not solely rely on this
           setting for security.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       PrivateDevices=
           Takes a boolean argument. If true, sets up a new /dev mount for the
           executed processes and only adds API pseudo devices such as
           /dev/null, /dev/zero or /dev/random (as well as the pseudo TTY
           subsystem) to it, but no physical devices such as /dev/sda, system
           memory /dev/mem, system ports /dev/port and others. This is useful
           to securely turn off physical device access by the executed
           process. Defaults to false. Enabling this option will install a
           system call filter to block low-level I/O system calls that are
           grouped in the @raw-io set, will also remove CAP_MKNOD and
           CAP_SYS_RAWIO from the capability bounding set for the unit (see
           above), and set DevicePolicy=closed (see systemd.resource-
           control(5) for details). Note that using this setting will
           disconnect propagation of mounts from the service to the host
           (propagation in the opposite direction continues to work). This
           means that this setting may not be used for services which shall be
           able to install mount points in the main mount namespace. The new
           /dev will be mounted read-only and 'noexec'. The latter may break
           old programs which try to set up executable memory by using mmap(2)
           of /dev/zero instead of using MAP_ANON. For this setting the same
           restrictions regarding mount propagation and privileges apply as
           for ReadOnlyPaths= and related calls, see above. If turned on and
           if running in user mode, or in system mode, but without the
           CAP_SYS_ADMIN capability (e.g. setting User=), NoNewPrivileges=yes
           is implied.

           Note that the implementation of this setting might be impossible
           (for example if mount namespaces are not available), and the unit
           should be written in a way that does not solely rely on this
           setting for security.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       PrivateNetwork=
           Takes a boolean argument. If true, sets up a new network namespace
           for the executed processes and configures only the loopback network
           device "lo" inside it. No other network devices will be available
           to the executed process. This is useful to turn off network access
           by the executed process. Defaults to false. It is possible to run
           two or more units within the same private network namespace by
           using the JoinsNamespaceOf= directive, see systemd.unit(5) for
           details. Note that this option will disconnect all socket families
           from the host, including AF_NETLINK and AF_UNIX. Effectively, for
           AF_NETLINK this means that device configuration events received
           from systemd-udevd.service(8) are not delivered to the unit's
           processes. And for AF_UNIX this has the effect that AF_UNIX sockets
           in the abstract socket namespace of the host will become
           unavailable to the unit's processes (however, those located in the
           file system will continue to be accessible).

           Note that the implementation of this setting might be impossible
           (for example if network namespaces are not available), and the unit
           should be written in a way that does not solely rely on this
           setting for security.

           When this option is used on a socket unit any sockets bound on
           behalf of this unit will be bound within a private network
           namespace. This may be combined with JoinsNamespaceOf= to listen on
           sockets inside of network namespaces of other services.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       NetworkNamespacePath=
           Takes an absolute file system path refererring to a Linux network
           namespace pseudo-file (i.e. a file like /proc/$PID/ns/net or a bind
           mount or symlink to one). When set the invoked processes are added
           to the network namespace referenced by that path. The path has to
           point to a valid namespace file at the moment the processes are
           forked off. If this option is used PrivateNetwork= has no effect.
           If this option is used together with JoinsNamespaceOf= then it only
           has an effect if this unit is started before any of the listed
           units that have PrivateNetwork= or NetworkNamespacePath=
           configured, as otherwise the network namespace of those units is
           reused.

           When this option is used on a socket unit any sockets bound on
           behalf of this unit will be bound within the specified network
           namespace.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       PrivateUsers=
           Takes a boolean argument. If true, sets up a new user namespace for
           the executed processes and configures a minimal user and group
           mapping, that maps the "root" user and group as well as the unit's
           own user and group to themselves and everything else to the
           "nobody" user and group. This is useful to securely detach the user
           and group databases used by the unit from the rest of the system,
           and thus to create an effective sandbox environment. All files,
           directories, processes, IPC objects and other resources owned by
           users/groups not equaling "root" or the unit's own will stay
           visible from within the unit but appear owned by the "nobody" user
           and group. If this mode is enabled, all unit processes are run
           without privileges in the host user namespace (regardless if the
           unit's own user/group is "root" or not). Specifically this means
           that the process will have zero process capabilities on the host's
           user namespace, but full capabilities within the service's user
           namespace. Settings such as CapabilityBoundingSet= will affect only
           the latter, and there's no way to acquire additional capabilities
           in the host's user namespace. Defaults to off.

           When this setting is set up by a per-user instance of the service
           manager, the mapping of the "root" user and group to itself is
           omitted (unless the user manager is root). Additionally, in the
           per-user instance manager case, the user namespace will be set up
           before most other namespaces. This means that combining
           PrivateUsers=true with other namespaces will enable use of features
           not normally supported by the per-user instances of the service
           manager.

           This setting is particularly useful in conjunction with
           RootDirectory=/RootImage=, as the need to synchronize the user and
           group databases in the root directory and on the host is reduced,
           as the only users and groups who need to be matched are "root",
           "nobody" and the unit's own user and group.

           Note that the implementation of this setting might be impossible
           (for example if user namespaces are not available), and the unit
           should be written in a way that does not solely rely on this
           setting for security.

       ProtectHostname=
           Takes a boolean argument. When set, sets up a new UTS namespace for
           the executed processes. In addition, changing hostname or
           domainname is prevented. Defaults to off.

           Note that the implementation of this setting might be impossible
           (for example if UTS namespaces are not available), and the unit
           should be written in a way that does not solely rely on this
           setting for security.

           Note that when this option is enabled for a service hostname
           changes no longer propagate from the system into the service, it is
           hence not suitable for services that need to take notice of system
           hostname changes dynamically.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       ProtectClock=
           Takes a boolean argument. If set, writes to the hardware clock or
           system clock will be denied. It is recommended to turn this on for
           most services that do not need modify the clock. Defaults to off.
           Enabling this option removes CAP_SYS_TIME and CAP_WAKE_ALARM from
           the capability bounding set for this unit, installs a system call
           filter to block calls that can set the clock, and
           DeviceAllow=char-rtc r is implied. This ensures /dev/rtc0,
           /dev/rtc1, etc are made read only to the service. See
           systemd.resource-control(5) for the details about DeviceAllow=.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       ProtectKernelTunables=
           Takes a boolean argument. If true, kernel variables accessible
           through /proc/sys, /sys, /proc/sysrq-trigger, /proc/latency_stats,
           /proc/acpi, /proc/timer_stats, /proc/fs and /proc/irq will be made
           read-only to all processes of the unit. Usually, tunable kernel
           variables should be initialized only at boot-time, for example with
           the sysctl.d(5) mechanism. Few services need to write to these at
           runtime; it is hence recommended to turn this on for most services.
           For this setting the same restrictions regarding mount propagation
           and privileges apply as for ReadOnlyPaths= and related calls, see
           above. Defaults to off. If turned on and if running in user mode,
           or in system mode, but without the CAP_SYS_ADMIN capability (e.g.
           services for which User= is set), NoNewPrivileges=yes is implied.
           Note that this option does not prevent indirect changes to kernel
           tunables effected by IPC calls to other processes. However,
           InaccessiblePaths= may be used to make relevant IPC file system
           objects inaccessible. If ProtectKernelTunables= is set,
           MountAPIVFS=yes is implied.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       ProtectKernelModules=
           Takes a boolean argument. If true, explicit module loading will be
           denied. This allows module load and unload operations to be turned
           off on modular kernels. It is recommended to turn this on for most
           services that do not need special file systems or extra kernel
           modules to work. Defaults to off. Enabling this option removes
           CAP_SYS_MODULE from the capability bounding set for the unit, and
           installs a system call filter to block module system calls, also
           /usr/lib/modules is made inaccessible. For this setting the same
           restrictions regarding mount propagation and privileges apply as
           for ReadOnlyPaths= and related calls, see above. Note that limited
           automatic module loading due to user configuration or kernel
           mapping tables might still happen as side effect of requested user
           operations, both privileged and unprivileged. To disable module
           auto-load feature please see sysctl.d(5) kernel.modules_disabled
           mechanism and /proc/sys/kernel/modules_disabled documentation. If
           turned on and if running in user mode, or in system mode, but
           without the CAP_SYS_ADMIN capability (e.g. setting User=),
           NoNewPrivileges=yes is implied.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       ProtectKernelLogs=
           Takes a boolean argument. If true, access to the kernel log ring
           buffer will be denied. It is recommended to turn this on for most
           services that do not need to read from or write to the kernel log
           ring buffer. Enabling this option removes CAP_SYSLOG from the
           capability bounding set for this unit, and installs a system call
           filter to block the syslog(2) system call (not to be confused with
           the libc API syslog(3) for userspace logging). The kernel exposes
           its log buffer to userspace via /dev/kmsg and /proc/kmsg. If
           enabled, these are made inaccessible to all the processes in the
           unit.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       ProtectControlGroups=
           Takes a boolean argument. If true, the Linux Control Groups
           (cgroups(7)) hierarchies accessible through /sys/fs/cgroup will be
           made read-only to all processes of the unit. Except for container
           managers no services should require write access to the control
           groups hierarchies; it is hence recommended to turn this on for
           most services. For this setting the same restrictions regarding
           mount propagation and privileges apply as for ReadOnlyPaths= and
           related calls, see above. Defaults to off. If ProtectControlGroups=
           is set, MountAPIVFS=yes is implied.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       RestrictAddressFamilies=
           Restricts the set of socket address families accessible to the
           processes of this unit. Takes a space-separated list of address
           family names to whitelist, such as AF_UNIX, AF_INET or AF_INET6.
           When prefixed with ~ the listed address families will be applied as
           blacklist, otherwise as whitelist. Note that this restricts access
           to the socket(2) system call only. Sockets passed into the process
           by other means (for example, by using socket activation with socket
           units, see systemd.socket(5)) are unaffected. Also, sockets created
           with socketpair() (which creates connected AF_UNIX sockets only)
           are unaffected. Note that this option has no effect on 32-bit x86,
           s390, s390x, mips, mips-le, ppc, ppc-le, pcc64, ppc64-le and is
           ignored (but works correctly on other ABIs, including x86-64). Note
           that on systems supporting multiple ABIs (such as x86/x86-64) it is
           recommended to turn off alternative ABIs for services, so that they
           cannot be used to circumvent the restrictions of this option.
           Specifically, it is recommended to combine this option with
           SystemCallArchitectures=native or similar. If running in user mode,
           or in system mode, but without the CAP_SYS_ADMIN capability (e.g.
           setting User=nobody), NoNewPrivileges=yes is implied. By default,
           no restrictions apply, all address families are accessible to
           processes. If assigned the empty string, any previous address
           family restriction changes are undone. This setting does not affect
           commands prefixed with "+".

           Use this option to limit exposure of processes to remote access, in
           particular via exotic and sensitive network protocols, such as
           AF_PACKET. Note that in most cases, the local AF_UNIX address
           family should be included in the configured whitelist as it is
           frequently used for local communication, including for syslog(2)
           logging.

       RestrictNamespaces=
           Restricts access to Linux namespace functionality for the processes
           of this unit. For details about Linux namespaces, see
           namespaces(7). Either takes a boolean argument, or a
           space-separated list of namespace type identifiers. If false (the
           default), no restrictions on namespace creation and switching are
           made. If true, access to any kind of namespacing is prohibited.
           Otherwise, a space-separated list of namespace type identifiers
           must be specified, consisting of any combination of: cgroup, ipc,
           net, mnt, pid, user and uts. Any namespace type listed is made
           accessible to the unit's processes, access to namespace types not
           listed is prohibited (whitelisting). By prepending the list with a
           single tilde character ("~") the effect may be inverted: only the
           listed namespace types will be made inaccessible, all unlisted ones
           are permitted (blacklisting). If the empty string is assigned, the
           default namespace restrictions are applied, which is equivalent to
           false. This option may appear more than once, in which case the
           namespace types are merged by OR, or by AND if the lines are
           prefixed with "~" (see examples below). Internally, this setting
           limits access to the unshare(2), clone(2) and setns(2) system
           calls, taking the specified flags parameters into account. Note
           that -- if this option is used -- in addition to restricting
           creation and switching of the specified types of namespaces (or all
           of them, if true) access to the setns() system call with a zero
           flags parameter is prohibited. This setting is only supported on
           x86, x86-64, mips, mips-le, mips64, mips64-le, mips64-n32,
           mips64-le-n32, ppc64, ppc64-le, s390 and s390x, and enforces no
           restrictions on other architectures. If running in user mode, or in
           system mode, but without the CAP_SYS_ADMIN capability (e.g. setting
           User=), NoNewPrivileges=yes is implied.

           Example: if a unit has the following,

               RestrictNamespaces=cgroup ipc
               RestrictNamespaces=cgroup net

           then cgroup, ipc, and net are set. If the second line is prefixed
           with "~", e.g.,

               RestrictNamespaces=cgroup ipc
               RestrictNamespaces=~cgroup net

           then, only ipc is set.

       LockPersonality=
           Takes a boolean argument. If set, locks down the personality(2)
           system call so that the kernel execution domain may not be changed
           from the default or the personality selected with Personality=
           directive. This may be useful to improve security, because odd
           personality emulations may be poorly tested and source of
           vulnerabilities. If running in user mode, or in system mode, but
           without the CAP_SYS_ADMIN capability (e.g. setting User=),
           NoNewPrivileges=yes is implied.

       MemoryDenyWriteExecute=
           Takes a boolean argument. If set, attempts to create memory
           mappings that are writable and executable at the same time, or to
           change existing memory mappings to become executable, or mapping
           shared memory segments as executable are prohibited. Specifically,
           a system call filter is added that rejects mmap(2) system calls
           with both PROT_EXEC and PROT_WRITE set, mprotect(2) or
           pkey_mprotect(2) system calls with PROT_EXEC set and shmat(2)
           system calls with SHM_EXEC set. Note that this option is
           incompatible with programs and libraries that generate program code
           dynamically at runtime, including JIT execution engines, executable
           stacks, and code "trampoline" feature of various C compilers. This
           option improves service security, as it makes harder for software
           exploits to change running code dynamically. However, the
           protection can be circumvented, if the service can write to a
           filesystem, which is not mounted with noexec (such as /dev/shm), or
           it can use memfd_create(). This can be prevented by making such
           file systems inaccessible to the service (e.g.
           InaccessiblePaths=/dev/shm) and installing further system call
           filters (SystemCallFilter=~memfd_create). Note that this feature is
           fully available on x86-64, and partially on x86. Specifically, the
           shmat() protection is not available on x86. Note that on systems
           supporting multiple ABIs (such as x86/x86-64) it is recommended to
           turn off alternative ABIs for services, so that they cannot be used
           to circumvent the restrictions of this option. Specifically, it is
           recommended to combine this option with
           SystemCallArchitectures=native or similar. If running in user mode,
           or in system mode, but without the CAP_SYS_ADMIN capability (e.g.
           setting User=), NoNewPrivileges=yes is implied.

       RestrictRealtime=
           Takes a boolean argument. If set, any attempts to enable realtime
           scheduling in a process of the unit are refused. This restricts
           access to realtime task scheduling policies such as SCHED_FIFO,
           SCHED_RR or SCHED_DEADLINE. See sched(7) for details about these
           scheduling policies. If running in user mode, or in system mode,
           but without the CAP_SYS_ADMIN capability (e.g. setting User=),
           NoNewPrivileges=yes is implied. Realtime scheduling policies may be
           used to monopolize CPU time for longer periods of time, and may
           hence be used to lock up or otherwise trigger Denial-of-Service
           situations on the system. It is hence recommended to restrict
           access to realtime scheduling to the few programs that actually
           require them. Defaults to off.

       RestrictSUIDSGID=
           Takes a boolean argument. If set, any attempts to set the
           set-user-ID (SUID) or set-group-ID (SGID) bits on files or
           directories will be denied (for details on these bits see
           inode(7)). If running in user mode, or in system mode, but without
           the CAP_SYS_ADMIN capability (e.g. setting User=),
           NoNewPrivileges=yes is implied. As the SUID/SGID bits are
           mechanisms to elevate privileges, and allows users to acquire the
           identity of other users, it is recommended to restrict creation of
           SUID/SGID files to the few programs that actually require them.
           Note that this restricts marking of any type of file system object
           with these bits, including both regular files and directories
           (where the SGID is a different meaning than for files, see
           documentation). This option is implied if DynamicUser= is enabled.
           Defaults to off.

       RemoveIPC=
           Takes a boolean parameter. If set, all System V and POSIX IPC
           objects owned by the user and group the processes of this unit are
           run as are removed when the unit is stopped. This setting only has
           an effect if at least one of User=, Group= and DynamicUser= are
           used. It has no effect on IPC objects owned by the root user.
           Specifically, this removes System V semaphores, as well as System V
           and POSIX shared memory segments and message queues. If multiple
           units use the same user or group the IPC objects are removed when
           the last of these units is stopped. This setting is implied if
           DynamicUser= is set.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       PrivateMounts=
           Takes a boolean parameter. If set, the processes of this unit will
           be run in their own private file system (mount) namespace with all
           mount propagation from the processes towards the host's main file
           system namespace turned off. This means any file system mount
           points established or removed by the unit's processes will be
           private to them and not be visible to the host. However, file
           system mount points established or removed on the host will be
           propagated to the unit's processes. See mount_namespaces(7) for
           details on file system namespaces. Defaults to off.

           When turned on, this executes three operations for each invoked
           process: a new CLONE_NEWNS namespace is created, after which all
           existing mounts are remounted to MS_SLAVE to disable propagation
           from the unit's processes to the host (but leaving propagation in
           the opposite direction in effect). Finally, the mounts are
           remounted again to the propagation mode configured with
           MountFlags=, see below.

           File system namespaces are set up individually for each process
           forked off by the service manager. Mounts established in the
           namespace of the process created by ExecStartPre= will hence be
           cleaned up automatically as soon as that process exits and will not
           be available to subsequent processes forked off for ExecStart= (and
           similar applies to the various other commands configured for
           units). Similarly, JoinsNamespaceOf= does not permit sharing kernel
           mount namespaces between units, it only enables sharing of the
           /tmp/ and /var/tmp/ directories.

           Other file system namespace unit settings -- PrivateMounts=,
           PrivateTmp=, PrivateDevices=, ProtectSystem=, ProtectHome=,
           ReadOnlyPaths=, InaccessiblePaths=, ReadWritePaths=, ... -- also
           enable file system namespacing in a fashion equivalent to this
           option. Hence it is primarily useful to explicitly request this
           behaviour if none of the other settings are used.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

       MountFlags=
           Takes a mount propagation setting: shared, slave or private, which
           controls whether file system mount points in the file system
           namespaces set up for this unit's processes will receive or
           propagate mounts and unmounts from other file system namespaces.
           See mount(2) for details on mount propagation, and the three
           propagation flags in particular.

           This setting only controls the final propagation setting in effect
           on all mount points of the file system namespace created for each
           process of this unit. Other file system namespacing unit settings
           (see the discussion in PrivateMounts= above) will implicitly
           disable mount and unmount propagation from the unit's processes
           towards the host by changing the propagation setting of all mount
           points in the unit's file system namepace to slave first. Setting
           this option to shared does not reestablish propagation in that
           case.

           If not set - but file system namespaces are enabled through another
           file system namespace unit setting - shared mount propagation is
           used, but -- as mentioned -- as slave is applied first, propagation
           from the unit's processes to the host is still turned off.

           It is not recommended to to use private mount propagation for
           units, as this means temporary mounts (such as removable media) of
           the host will stay mounted and thus indefinitely busy in forked off
           processes, as unmount propagation events won't be received by the
           file system namespace of the unit.

           Usually, it is best to leave this setting unmodified, and use
           higher level file system namespacing options instead, in particular
           PrivateMounts=, see above.

           This option is only available for system services and is not
           supported for services running in per-user instances of the service
           manager.

SYSTEM CALL FILTERING
       SystemCallFilter=
           Takes a space-separated list of system call names. If this setting
           is used, all system calls executed by the unit processes except for
           the listed ones will result in immediate process termination with
           the SIGSYS signal (whitelisting). (See SystemCallErrorNumber= below
           for changing the default action). If the first character of the
           list is "~", the effect is inverted: only the listed system calls
           will result in immediate process termination (blacklisting).
           Blacklisted system calls and system call groups may optionally be
           suffixed with a colon (":") and "errno" error number (between 0 and
           4095) or errno name such as EPERM, EACCES or EUCLEAN (see errno(3)
           for a full list). This value will be returned when a blacklisted
           system call is triggered, instead of terminating the processes
           immediately. This value takes precedence over the one given in
           SystemCallErrorNumber=, see below. If running in user mode, or in
           system mode, but without the CAP_SYS_ADMIN capability (e.g. setting
           User=nobody), NoNewPrivileges=yes is implied. This feature makes
           use of the Secure Computing Mode 2 interfaces of the kernel
           ('seccomp filtering') and is useful for enforcing a minimal
           sandboxing environment. Note that the execve, exit, exit_group,
           getrlimit, rt_sigreturn, sigreturn system calls and the system
           calls for querying time and sleeping are implicitly whitelisted and
           do not need to be listed explicitly. This option may be specified
           more than once, in which case the filter masks are merged. If the
           empty string is assigned, the filter is reset, all prior
           assignments will have no effect. This does not affect commands
           prefixed with "+".

           Note that on systems supporting multiple ABIs (such as x86/x86-64)
           it is recommended to turn off alternative ABIs for services, so
           that they cannot be used to circumvent the restrictions of this
           option. Specifically, it is recommended to combine this option with
           SystemCallArchitectures=native or similar.

           Note that strict system call filters may impact execution and error
           handling code paths of the service invocation. Specifically, access
           to the execve system call is required for the execution of the
           service binary -- if it is blocked service invocation will
           necessarily fail. Also, if execution of the service binary fails
           for some reason (for example: missing service executable), the
           error handling logic might require access to an additional set of
           system calls in order to process and log this failure correctly. It
           might be necessary to temporarily disable system call filters in
           order to simplify debugging of such failures.

           If you specify both types of this option (i.e. whitelisting and
           blacklisting), the first encountered will take precedence and will
           dictate the default action (termination or approval of a system
           call). Then the next occurrences of this option will add or delete
           the listed system calls from the set of the filtered system calls,
           depending of its type and the default action. (For example, if you
           have started with a whitelisting of read and write, and right after
           it add a blacklisting of write, then write will be removed from the
           set.)

           As the number of possible system calls is large, predefined sets of
           system calls are provided. A set starts with "@" character,
           followed by name of the set.

           Table 3. Currently predefined system call sets
           +----------------+----------------------------+
           |Set             | Description                |
           +----------------+----------------------------+
           |@aio            | Asynchronous I/O           |
           |                | (io_setup(2),              |
           |                | io_submit(2), and related  |
           |                | calls)                     |
           +----------------+----------------------------+
           |@basic-io       | System calls for basic     |
           |                | I/O: reading, writing,     |
           |                | seeking, file descriptor   |
           |                | duplication and closing    |
           |                | (read(2), write(2), and    |
           |                | related calls)             |
           +----------------+----------------------------+
           |@chown          | Changing file ownership    |
           |                | (chown(2), fchownat(2),    |
           |                | and related calls)         |
           +----------------+----------------------------+
           |@clock          | System calls for changing  |
           |                | the system clock           |
           |                | (adjtimex(2),              |
           |                | settimeofday(2), and       |
           |                | related calls)             |
           +----------------+----------------------------+
           |@cpu-emulation  | System calls for CPU       |
           |                | emulation functionality    |
           |                | (vm86(2) and related       |
           |                | calls)                     |
           +----------------+----------------------------+
           |@debug          | Debugging, performance     |
           |                | monitoring and tracing     |
           |                | functionality (ptrace(2),  |
           |                | perf_event_open(2) and     |
           |                | related calls)             |
           +----------------+----------------------------+
           |@file-system    | File system operations:    |
           |                | opening, creating files    |
           |                | and directories for read   |
           |                | and write, renaming and    |
           |                | removing them, reading     |
           |                | file properties, or        |
           |                | creating hard and symbolic |
           |                | links.                     |
           +----------------+----------------------------+
           |@io-event       | Event loop system calls    |
           |                | (poll(2), select(2),       |
           |                | epoll(7), eventfd(2) and   |
           |                | related calls)             |
           +----------------+----------------------------+
           |@ipc            | Pipes, SysV IPC, POSIX     |
           |                | Message Queues and other   |
           |                | IPC (mq_overview(7),       |
           |                | svipc(7))                  |
           +----------------+----------------------------+
           |@keyring        | Kernel keyring access      |
           |                | (keyctl(2) and related     |
           |                | calls)                     |
           +----------------+----------------------------+
           |@memlock        | Locking of memory into RAM |
           |                | (mlock(2), mlockall(2) and |
           |                | related calls)             |
           +----------------+----------------------------+
           |@module         | Loading and unloading of   |
           |                | kernel modules             |
           |                | (init_module(2),           |
           |                | delete_module(2) and       |
           |                | related calls)             |
           +----------------+----------------------------+
           |@mount          | Mounting and unmounting of |
           |                | file systems (mount(2),    |
           |                | chroot(2), and related     |
           |                | calls)                     |
           +----------------+----------------------------+
           |@network-io     | Socket I/O (including      |
           |                | local AF_UNIX): socket(7), |
           |                | unix(7)                    |
           +----------------+----------------------------+
           |@obsolete       | Unusual, obsolete or       |
           |                | unimplemented              |
           |                | (create_module(2),         |
           |                | gtty(2), ...)              |
           +----------------+----------------------------+
           |@privileged     | All system calls which     |
           |                | need super-user            |
           |                | capabilities               |
           |                | (capabilities(7))          |
           +----------------+----------------------------+
           |@process        | Process control,           |
           |                | execution, namespaceing    |
           |                | operations (clone(2),      |
           |                | kill(2), namespaces(7),    |
           |                | ...                        |
           +----------------+----------------------------+
           |@raw-io         | Raw I/O port access        |
           |                | (ioperm(2), iopl(2),       |
           |                | pciconfig_read(), ...)     |
           +----------------+----------------------------+
           |@reboot         | System calls for rebooting |
           |                | and reboot preparation     |
           |                | (reboot(2), kexec(), ...)  |
           +----------------+----------------------------+
           |@resources      | System calls for changing  |
           |                | resource limits, memory    |
           |                | and scheduling parameters  |
           |                | (setrlimit(2),             |
           |                | setpriority(2), ...)       |
           +----------------+----------------------------+
           |@setuid         | System calls for changing  |
           |                | user ID and group ID       |
           |                | credentials, (setuid(2),   |
           |                | setgid(2), setresuid(2),   |
           |                | ...)                       |
           +----------------+----------------------------+
           |@signal         | System calls for           |
           |                | manipulating and handling  |
           |                | process signals            |
           |                | (signal(2),                |
           |                | sigprocmask(2), ...)       |
           +----------------+----------------------------+
           |@swap           | System calls for           |
           |                | enabling/disabling swap    |
           |                | devices (swapon(2),        |
           |                | swapoff(2))                |
           +----------------+----------------------------+
           |@sync           | Synchronizing files and    |
           |                | memory to disk: (fsync(2), |
           |                | msync(2), and related      |
           |                | calls)                     |
           +----------------+----------------------------+
           |@system-service | A reasonable set of system |
           |                | calls used by common       |
           |                | system services, excluding |
           |                | any special purpose calls. |
           |                | This is the recommended    |
           |                | starting point for         |
           |                | whitelisting system calls  |
           |                | for system services, as it |
           |                | contains what is typically |
           |                | needed by system services, |
           |                | but excludes overly        |
           |                | specific interfaces. For   |
           |                | example, the following     |
           |                | APIs are excluded:         |
           |                | "@clock", "@mount",        |
           |                | "@swap", "@reboot".        |
           +----------------+----------------------------+
           |@timer          | System calls for           |
           |                | scheduling operations by   |
           |                | time (alarm(2),            |
           |                | timer_create(2), ...)      |
           +----------------+----------------------------+
           Note, that as new system calls are added to the kernel, additional
           system calls might be added to the groups above. Contents of the
           sets may also change between systemd versions. In addition, the
           list of system calls depends on the kernel version and architecture
           for which systemd was compiled. Use systemd-analyze syscall-filter
           to list the actual list of system calls in each filter.

           Generally, whitelisting system calls (rather than blacklisting) is
           the safer mode of operation. It is recommended to enforce system
           call whitelists for all long-running system services. Specifically,
           the following lines are a relatively safe basic choice for the
           majority of system services:

               [Service]
               SystemCallFilter=@system-service
               SystemCallErrorNumber=EPERM

           Note that various kernel system calls are defined redundantly:
           there are multiple system calls for executing the same operation.
           For example, the pidfd_send_signal() system call may be used to
           execute operations similar to what can be done with the older
           kill() system call, hence blocking the latter without the former
           only provides weak protection. Since new system calls are added
           regularly to the kernel as development progresses, keeping system
           call blacklists comprehensive requires constant work. It is thus
           recommended to use whitelisting instead, which offers the benefit
           that new system calls are by default implicitly blocked until the
           whitelist is updated.

           Also note that a number of system calls are required to be
           accessible for the dynamic linker to work. The dynamic linker is
           required for running most regular programs (specifically: all
           dynamic ELF binaries, which is how most distributions build
           packaged programs). This means that blocking these system calls
           (which include open(), openat() or mmap()) will make most programs
           typically shipped with generic distributions unusable.

           It is recommended to combine the file system namespacing related
           options with SystemCallFilter=~@mount, in order to prohibit the
           unit's processes to undo the mappings. Specifically these are the
           options PrivateTmp=, PrivateDevices=, ProtectSystem=, ProtectHome=,
           ProtectKernelTunables=, ProtectControlGroups=, ProtectKernelLogs=,
           ProtectClock=, ReadOnlyPaths=, InaccessiblePaths= and
           ReadWritePaths=.

       SystemCallErrorNumber=
           Takes an "errno" error number (between 1 and 4095) or errno name
           such as EPERM, EACCES or EUCLEAN, to return when the system call
           filter configured with SystemCallFilter= is triggered, instead of
           terminating the process immediately. See errno(3) for a full list
           of error codes. When this setting is not used, or when the empty
           string is assigned, the process will be terminated immediately when
           the filter is triggered.

       SystemCallArchitectures=
           Takes a space-separated list of architecture identifiers to include
           in the system call filter. The known architecture identifiers are
           the same as for ConditionArchitecture= described in
           systemd.unit(5), as well as x32, mips64-n32, mips64-le-n32, and the
           special identifier native. The special identifier native implicitly
           maps to the native architecture of the system (or more precisely:
           to the architecture the system manager is compiled for). If running
           in user mode, or in system mode, but without the CAP_SYS_ADMIN
           capability (e.g. setting User=nobody), NoNewPrivileges=yes is
           implied. By default, this option is set to the empty list, i.e. no
           system call architecture filtering is applied.

           If this setting is used, processes of this unit will only be
           permitted to call native system calls, and system calls of the
           specified architectures. For the purposes of this option, the x32
           architecture is treated as including x86-64 system calls. However,
           this setting still fulfills its purpose, as explained below, on
           x32.

           System call filtering is not equally effective on all
           architectures. For example, on x86 filtering of network
           socket-related calls is not possible, due to ABI limitations -- a
           limitation that x86-64 does not have, however. On systems
           supporting multiple ABIs at the same time -- such as x86/x86-64 --
           it is hence recommended to limit the set of permitted system call
           architectures so that secondary ABIs may not be used to circumvent
           the restrictions applied to the native ABI of the system. In
           particular, setting SystemCallArchitectures=native is a good choice
           for disabling non-native ABIs.

           System call architectures may also be restricted system-wide via
           the SystemCallArchitectures= option in the global configuration.
           See systemd-system.conf(5) for details.

ENVIRONMENT
       Environment=
           Sets environment variables for executed processes. Takes a
           space-separated list of variable assignments. This option may be
           specified more than once, in which case all listed variables will
           be set. If the same variable is set twice, the later setting will
           override the earlier setting. If the empty string is assigned to
           this option, the list of environment variables is reset, all prior
           assignments have no effect. Variable expansion is not performed
           inside the strings, however, specifier expansion is possible. The $
           character has no special meaning. If you need to assign a value
           containing spaces or the equals sign to a variable, use double
           quotes (") for the assignment.

           Example:

               Environment="VAR1=word1 word2" VAR2=word3 "VAR3=$word 5 6"

           gives three variables "VAR1", "VAR2", "VAR3" with the values "word1
           word2", "word3", "$word 5 6".

           See environ(7) for details about environment variables.

           Note that environment variables are not suitable for passing
           secrets (such as passwords, key material, ...) to service
           processes. Environment variables set for a unit are exposed to
           unprivileged clients via D-Bus IPC, and generally not understood as
           being data that requires protection. Moreover, environment
           variables are propagated down the process tree, including across
           security boundaries (such as setuid/setgid executables), and hence
           might leak to processes that should not have access to the secret
           data.

       EnvironmentFile=
           Similar to Environment= but reads the environment variables from a
           text file. The text file should contain new-line-separated variable
           assignments. Empty lines, lines without an "=" separator, or lines
           starting with ; or # will be ignored, which may be used for
           commenting. A line ending with a backslash will be concatenated
           with the following one, allowing multiline variable definitions.
           The parser strips leading and trailing whitespace from the values
           of assignments, unless you use double quotes (").

           C escapes[5] are supported, but not most control characters[6].
           "\t" and "\n" can be used to insert tabs and newlines within
           EnvironmentFile=.

           The argument passed should be an absolute filename or wildcard
           expression, optionally prefixed with "-", which indicates that if
           the file does not exist, it will not be read and no error or
           warning message is logged. This option may be specified more than
           once in which case all specified files are read. If the empty
           string is assigned to this option, the list of file to read is
           reset, all prior assignments have no effect.

           The files listed with this directive will be read shortly before
           the process is executed (more specifically, after all processes
           from a previous unit state terminated. This means you can generate
           these files in one unit state, and read it with this option in the
           next. The files are read from the file system of the service
           manager, before any file system changes like bind mounts take
           place).

           Settings from these files override settings made with Environment=.
           If the same variable is set twice from these files, the files will
           be read in the order they are specified and the later setting will
           override the earlier setting.

       PassEnvironment=
           Pass environment variables set for the system service manager to
           executed processes. Takes a space-separated list of variable names.
           This option may be specified more than once, in which case all
           listed variables will be passed. If the empty string is assigned to
           this option, the list of environment variables to pass is reset,
           all prior assignments have no effect. Variables specified that are
           not set for the system manager will not be passed and will be
           silently ignored. Note that this option is only relevant for the
           system service manager, as system services by default do not
           automatically inherit any environment variables set for the service
           manager itself. However, in case of the user service manager all
           environment variables are passed to the executed processes anyway,
           hence this option is without effect for the user service manager.

           Variables set for invoked processes due to this setting are subject
           to being overridden by those configured with Environment= or
           EnvironmentFile=.

           C escapes[5] are supported, but not most control characters[6].
           "\t" and "\n" can be used to insert tabs and newlines within
           EnvironmentFile=.

           Example:

               PassEnvironment=VAR1 VAR2 VAR3

           passes three variables "VAR1", "VAR2", "VAR3" with the values set
           for those variables in PID1.

           See environ(7) for details about environment variables.

       UnsetEnvironment=
           Explicitly unset environment variable assignments that would
           normally be passed from the service manager to invoked processes of
           this unit. Takes a space-separated list of variable names or
           variable assignments. This option may be specified more than once,
           in which case all listed variables/assignments will be unset. If
           the empty string is assigned to this option, the list of
           environment variables/assignments to unset is reset. If a variable
           assignment is specified (that is: a variable name, followed by "=",
           followed by its value), then any environment variable matching this
           precise assignment is removed. If a variable name is specified
           (that is a variable name without any following "=" or value), then
           any assignment matching the variable name, regardless of its value
           is removed. Note that the effect of UnsetEnvironment= is applied as
           final step when the environment list passed to executed processes
           is compiled. That means it may undo assignments from any
           configuration source, including assignments made through
           Environment= or EnvironmentFile=, inherited from the system
           manager's global set of environment variables, inherited via
           PassEnvironment=, set by the service manager itself (such as
           $NOTIFY_SOCKET and such), or set by a PAM module (in case PAMName=
           is used).

           See environ(7) for details about environment variables.

LOGGING AND STANDARD INPUT/OUTPUT
       StandardInput=
           Controls where file descriptor 0 (STDIN) of the executed processes
           is connected to. Takes one of null, tty, tty-force, tty-fail, data,
           file:path, socket or fd:name.

           If null is selected, standard input will be connected to /dev/null,
           i.e. all read attempts by the process will result in immediate EOF.

           If tty is selected, standard input is connected to a TTY (as
           configured by TTYPath=, see below) and the executed process becomes
           the controlling process of the terminal. If the terminal is already
           being controlled by another process, the executed process waits
           until the current controlling process releases the terminal.

           tty-force is similar to tty, but the executed process is forcefully
           and immediately made the controlling process of the terminal,
           potentially removing previous controlling processes from the
           terminal.

           tty-fail is similar to tty, but if the terminal already has a
           controlling process start-up of the executed process fails.

           The data option may be used to configure arbitrary textual or
           binary data to pass via standard input to the executed process. The
           data to pass is configured via
           StandardInputText=/StandardInputData= (see below). Note that the
           actual file descriptor type passed (memory file, regular file, UNIX
           pipe, ...) might depend on the kernel and available privileges. In
           any case, the file descriptor is read-only, and when read returns
           the specified data followed by EOF.

           The file:path option may be used to connect a specific file system
           object to standard input. An absolute path following the ":"
           character is expected, which may refer to a regular file, a FIFO or
           special file. If an AF_UNIX socket in the file system is specified,
           a stream socket is connected to it. The latter is useful for
           connecting standard input of processes to arbitrary system
           services.

           The socket option is valid in socket-activated services only, and
           requires the relevant socket unit file (see systemd.socket(5) for
           details) to have Accept=yes set, or to specify a single socket
           only. If this option is set, standard input will be connected to
           the socket the service was activated from, which is primarily
           useful for compatibility with daemons designed for use with the
           traditional inetd(8) socket activation daemon.

           The fd:name option connects standard input to a specific, named
           file descriptor provided by a socket unit. The name may be
           specified as part of this option, following a ":" character (e.g.
           "fd:foobar"). If no name is specified, the name "stdin" is implied
           (i.e.  "fd" is equivalent to "fd:stdin"). At least one socket unit
           defining the specified name must be provided via the Sockets=
           option, and the file descriptor name may differ from the name of
           its containing socket unit. If multiple matches are found, the
           first one will be used. See FileDescriptorName= in
           systemd.socket(5) for more details about named file descriptors and
           their ordering.

           This setting defaults to null.

           Note that services which specify DefaultDependencies=no and use
           StandardInput= or StandardOutput= with tty/tty-force/tty-fail,
           should specify After=systemd-vconsole-setup.service, to make sure
           that the tty initialization is finished before they start.

       StandardOutput=
           Controls where file descriptor 1 (stdout) of the executed processes
           is connected to. Takes one of inherit, null, tty, journal, kmsg,
           journal+console, kmsg+console, file:path, append:path, socket or
           fd:name.

           inherit duplicates the file descriptor of standard input for
           standard output.

           null connects standard output to /dev/null, i.e. everything written
           to it will be lost.

           tty connects standard output to a tty (as configured via TTYPath=,
           see below). If the TTY is used for output only, the executed
           process will not become the controlling process of the terminal,
           and will not fail or wait for other processes to release the
           terminal.

           journal connects standard output with the journal, which is
           accessible via journalctl(1). Note that everything that is written
           to kmsg (see below) is implicitly stored in the journal as well,
           the specific option listed below is hence a superset of this one.
           (Also note that any external, additional syslog daemons receive
           their log data from the journal, too, hence this is the option to
           use when logging shall be processed with such a daemon.)

           kmsg connects standard output with the kernel log buffer which is
           accessible via dmesg(1), in addition to the journal. The journal
           daemon might be configured to send all logs to kmsg anyway, in
           which case this option is no different from journal.

           journal+console and kmsg+console work in a similar way as the two
           options above but copy the output to the system console as well.

           The file:path option may be used to connect a specific file system
           object to standard output. The semantics are similar to the same
           option of StandardInput=, see above. If path refers to a regular
           file on the filesystem, it is opened (created if it doesn't exist
           yet) for writing at the beginning of the file, but without
           truncating it. If standard input and output are directed to the
           same file path, it is opened only once, for reading as well as
           writing and duplicated. This is particularly useful when the
           specified path refers to an AF_UNIX socket in the file system, as
           in that case only a single stream connection is created for both
           input and output.

           append:path is similar to file:path above, but it opens the file in
           append mode.

           socket connects standard output to a socket acquired via socket
           activation. The semantics are similar to the same option of
           StandardInput=, see above.

           The fd:name option connects standard output to a specific, named
           file descriptor provided by a socket unit. A name may be specified
           as part of this option, following a ":" character (e.g.
           "fd:foobar"). If no name is specified, the name "stdout" is implied
           (i.e.  "fd" is equivalent to "fd:stdout"). At least one socket unit
           defining the specified name must be provided via the Sockets=
           option, and the file descriptor name may differ from the name of
           its containing socket unit. If multiple matches are found, the
           first one will be used. See FileDescriptorName= in
           systemd.socket(5) for more details about named descriptors and
           their ordering.

           If the standard output (or error output, see below) of a unit is
           connected to the journal or the kernel log buffer, the unit will
           implicitly gain a dependency of type After= on
           systemd-journald.socket (also see the "Implicit Dependencies"
           section above). Also note that in this case stdout (or stderr, see
           below) will be an AF_UNIX stream socket, and not a pipe or FIFO
           that can be re-opened. This means when executing shell scripts the
           construct echo "hello" > /dev/stderr for writing text to stderr
           will not work. To mitigate this use the construct echo "hello" >&2
           instead, which is mostly equivalent and avoids this pitfall.

           This setting defaults to the value set with DefaultStandardOutput=
           in systemd-system.conf(5), which defaults to journal. Note that
           setting this parameter might result in additional dependencies to
           be added to the unit (see above).

       StandardError=
           Controls where file descriptor 2 (stderr) of the executed processes
           is connected to. The available options are identical to those of
           StandardOutput=, with some exceptions: if set to inherit the file
           descriptor used for standard output is duplicated for standard
           error, while fd:name will use a default file descriptor name of
           "stderr".

           This setting defaults to the value set with DefaultStandardError=
           in systemd-system.conf(5), which defaults to inherit. Note that
           setting this parameter might result in additional dependencies to
           be added to the unit (see above).

       StandardInputText=, StandardInputData=
           Configures arbitrary textual or binary data to pass via file
           descriptor 0 (STDIN) to the executed processes. These settings have
           no effect unless StandardInput= is set to data. Use this option to
           embed process input data directly in the unit file.

           StandardInputText= accepts arbitrary textual data. C-style escapes
           for special characters as well as the usual "%"-specifiers are
           resolved. Each time this setting is used the specified text is
           appended to the per-unit data buffer, followed by a newline
           character (thus every use appends a new line to the end of the
           buffer). Note that leading and trailing whitespace of lines
           configured with this option is removed. If an empty line is
           specified the buffer is cleared (hence, in order to insert an empty
           line, add an additional "\n" to the end or beginning of a line).

           StandardInputData= accepts arbitrary binary data, encoded in
           Base64[7]. No escape sequences or specifiers are resolved. Any
           whitespace in the encoded version is ignored during decoding.

           Note that StandardInputText= and StandardInputData= operate on the
           same data buffer, and may be mixed in order to configure both
           binary and textual data for the same input stream. The textual or
           binary data is joined strictly in the order the settings appear in
           the unit file. Assigning an empty string to either will reset the
           data buffer.

           Please keep in mind that in order to maintain readability long unit
           file settings may be split into multiple lines, by suffixing each
           line (except for the last) with a "\" character (see
           systemd.unit(5) for details). This is particularly useful for large
           data configured with these two options. Example:

               ...
               StandardInput=data
               StandardInputData=SWNrIHNpdHplIGRhIHVuJyBlc3NlIEtsb3BzLAp1ZmYgZWVtYWwga2xvcHAncy4KSWNrIGtpZWtl \
                                 LCBzdGF1bmUsIHd1bmRyZSBtaXIsCnVmZiBlZW1hbCBqZWh0IHNlIHVmZiBkaWUgVMO8ci4KTmFu \
                                 dSwgZGVuayBpY2ssIGljayBkZW5rIG5hbnUhCkpldHogaXNzZSB1ZmYsIGVyc2NodCB3YXIgc2Ug \
                                 enUhCkljayBqZWhlIHJhdXMgdW5kIGJsaWNrZSDigJQKdW5kIHdlciBzdGVodCBkcmF1w59lbj8g \
                                 SWNrZSEK
               ...

       LogLevelMax=
           Configures filtering by log level of log messages generated by this
           unit. Takes a syslog log level, one of emerg (lowest log level,
           only highest priority messages), alert, crit, err, warning, notice,
           info, debug (highest log level, also lowest priority messages). See
           syslog(3) for details. By default no filtering is applied (i.e. the
           default maximum log level is debug). Use this option to configure
           the logging system to drop log messages of a specific service above
           the specified level. For example, set LogLevelMax=info in order to
           turn off debug logging of a particularly chatty unit. Note that the
           configured level is applied to any log messages written by any of
           the processes belonging to this unit, sent via any supported
           logging protocol. The filtering is applied early in the logging
           pipeline, before any kind of further processing is done. Moreover,
           messages which pass through this filter successfully might still be
           dropped by filters applied at a later stage in the logging
           subsystem. For example, MaxLevelStore= configured in
           journald.conf(5) might prohibit messages of higher log levels to be
           stored on disk, even though the per-unit LogLevelMax= permitted it
           to be processed.

       LogExtraFields=
           Configures additional log metadata fields to include in all log
           records generated by processes associated with this unit. This
           setting takes one or more journal field assignments in the format
           "FIELD=VALUE" separated by whitespace. See systemd.journal-
           fields(7) for details on the journal field concept. Even though the
           underlying journal implementation permits binary field values, this
           setting accepts only valid UTF-8 values. To include space
           characters in a journal field value, enclose the assignment in
           double quotes (").  The usual specifiers are expanded in all
           assignments (see below). Note that this setting is not only useful
           for attaching additional metadata to log records of a unit, but
           given that all fields and values are indexed may also be used to
           implement cross-unit log record matching. Assign an empty string to
           reset the list.

       LogRateLimitIntervalSec=, LogRateLimitBurst=
           Configures the rate limiting that is applied to messages generated
           by this unit. If, in the time interval defined by
           LogRateLimitIntervalSec=, more messages than specified in
           LogRateLimitBurst= are logged by a service, all further messages
           within the interval are dropped until the interval is over. A
           message about the number of dropped messages is generated. The time
           specification for LogRateLimitIntervalSec= may be specified in the
           following units: "s", "min", "h", "ms", "us" (see systemd.time(7)
           for details). The default settings are set by RateLimitIntervalSec=
           and RateLimitBurst= configured in journald.conf(5).

       LogNamespace=
           Run the unit's processes in the specified journal namespace.
           Expects a short user-defined string identifying the namespace. If
           not used the processes of the service are run in the default
           journal namespace, i.e. their log stream is collected and processed
           by systemd-journald.service. If this option is used any log data
           generated by processes of this unit (regardless if via the
           syslog(), journal native logging or stdout/stderr logging) is
           collected and processed by an instance of the
           systemd-journald@.service template unit, which manages the
           specified namespace. The log data is stored in a data store
           independent from the default log namespace's data store. See
           systemd-journald.service(8) for details about journal namespaces.

           Internally, journal namespaces are implemented through Linux mount
           namespacing and over-mounting the directory that contains the
           relevant AF_UNIX sockets used for logging in the unit's mount
           namespace. Since mount namespaces are used this setting disconnects
           propagation of mounts from the unit's processes to the host,
           similar to how ReadOnlyPaths= and similar settings (see above)
           work. Journal namespaces may hence not be used for services that
           need to establish mount points on the host.

           When this option is used the unit will automatically gain ordering
           and requirement dependencies on the two socket units associated
           with the systemd-journald@.service instance so that they are
           automatically established prior to the unit starting up. Note that
           when this option is used log output of this service does not appear
           in the regular journalctl(1) output, unless the --namespace= option
           is used.

       SyslogIdentifier=
           Sets the process name ("syslog tag") to prefix log lines sent to
           the logging system or the kernel log buffer with. If not set,
           defaults to the process name of the executed process. This option
           is only useful when StandardOutput= or StandardError= are set to
           journal or kmsg (or to the same settings in combination with
           +console) and only applies to log messages written to stdout or
           stderr.

       SyslogFacility=
           Sets the syslog facility identifier to use when logging. One of
           kern, user, mail, daemon, auth, syslog, lpr, news, uucp, cron,
           authpriv, ftp, local0, local1, local2, local3, local4, local5,
           local6 or local7. See syslog(3) for details. This option is only
           useful when StandardOutput= or StandardError= are set to journal or
           kmsg (or to the same settings in combination with +console), and
           only applies to log messages written to stdout or stderr. Defaults
           to daemon.

       SyslogLevel=
           The default syslog log level to use when logging to the logging
           system or the kernel log buffer. One of emerg, alert, crit, err,
           warning, notice, info, debug. See syslog(3) for details. This
           option is only useful when StandardOutput= or StandardError= are
           set to journal or kmsg (or to the same settings in combination with
           +console), and only applies to log messages written to stdout or
           stderr. Note that individual lines output by executed processes may
           be prefixed with a different log level which can be used to
           override the default log level specified here. The interpretation
           of these prefixes may be disabled with SyslogLevelPrefix=, see
           below. For details, see sd-daemon(3). Defaults to info.

       SyslogLevelPrefix=
           Takes a boolean argument. If true and StandardOutput= or
           StandardError= are set to journal or kmsg (or to the same settings
           in combination with +console), log lines written by the executed
           process that are prefixed with a log level will be processed with
           this log level set but the prefix removed. If set to false, the
           interpretation of these prefixes is disabled and the logged lines
           are passed on as-is. This only applies to log messages written to
           stdout or stderr. For details about this prefixing see sd-
           daemon(3). Defaults to true.

       TTYPath=
           Sets the terminal device node to use if standard input, output, or
           error are connected to a TTY (see above). Defaults to /dev/console.

       TTYReset=
           Reset the terminal device specified with TTYPath= before and after
           execution. Defaults to "no".

       TTYVHangup=
           Disconnect all clients which have opened the terminal device
           specified with TTYPath= before and after execution. Defaults to
           "no".

       TTYVTDisallocate=
           If the terminal device specified with TTYPath= is a virtual console
           terminal, try to deallocate the TTY before and after execution.
           This ensures that the screen and scrollback buffer is cleared.
           Defaults to "no".

SYSTEM V COMPATIBILITY
       UtmpIdentifier=
           Takes a four character identifier string for an utmp(5) and wtmp
           entry for this service. This should only be set for services such
           as getty implementations (such as agetty(8)) where utmp/wtmp
           entries must be created and cleared before and after execution, or
           for services that shall be executed as if they were run by a getty
           process (see below). If the configured string is longer than four
           characters, it is truncated and the terminal four characters are
           used. This setting interprets %I style string replacements. This
           setting is unset by default, i.e. no utmp/wtmp entries are created
           or cleaned up for this service.

       UtmpMode=
           Takes one of "init", "login" or "user". If UtmpIdentifier= is set,
           controls which type of utmp(5)/wtmp entries for this service are
           generated. This setting has no effect unless UtmpIdentifier= is set
           too. If "init" is set, only an INIT_PROCESS entry is generated and
           the invoked process must implement a getty-compatible utmp/wtmp
           logic. If "login" is set, first an INIT_PROCESS entry, followed by
           a LOGIN_PROCESS entry is generated. In this case, the invoked
           process must implement a login(1)-compatible utmp/wtmp logic. If
           "user" is set, first an INIT_PROCESS entry, then a LOGIN_PROCESS
           entry and finally a USER_PROCESS entry is generated. In this case,
           the invoked process may be any process that is suitable to be run
           as session leader. Defaults to "init".

ENVIRONMENT VARIABLES IN SPAWNED PROCESSES
       Processes started by the service manager are executed with an
       environment variable block assembled from multiple sources. Processes
       started by the system service manager generally do not inherit
       environment variables set for the service manager itself (but this may
       be altered via PassEnvironment=), but processes started by the user
       service manager instances generally do inherit all environment
       variables set for the service manager itself.

       For each invoked process the list of environment variables set is
       compiled from the following sources:

       o   Variables globally configured for the service manager, using the
           DefaultEnvironment= setting in systemd-system.conf(5), the kernel
           command line option systemd.setenv= (see systemd(1)) or via
           systemctl set-environment (see systemctl(1)).

       o   Variables defined by the service manager itself (see the list
           below)

       o   Variables set in the service manager's own environment variable
           block (subject to PassEnvironment= for the system service manager)

       o   Variables set via Environment= in the unit file

       o   Variables read from files specified via EnvironmentFile= in the
           unit file

       o   Variables set by any PAM modules in case PAMName= is in effect,
           cf. pam_env(8)

       If the same environment variables are set by multiple of these sources,
       the later source -- according to the order of the list above -- wins.
       Note that as final step all variables listed in UnsetEnvironment= are
       removed again from the compiled environment variable list, immediately
       before it is passed to the executed process.

       The following select environment variables are set or propagated by the
       service manager for each invoked process:

       $PATH
           Colon-separated list of directories to use when launching
           executables.  systemd uses a fixed value of
           "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin" in the system
           manager. When compiled for systems with "unmerged /usr" (/bin is
           not a symlink to /usr/bin), ":/sbin:/bin" is appended. In case of
           the the user manager, a different path may be configured by the
           distribution. It is recommended to not rely on the order of
           entries, and have only one program with a given name in $PATH.

       $LANG
           Locale. Can be set in locale.conf(5) or on the kernel command line
           (see systemd(1) and kernel-command-line(7)).

       $USER, $LOGNAME, $HOME, $SHELL
           User name (twice), home directory, and the login shell. The
           variables are set for the units that have User= set, which includes
           user systemd instances. See passwd(5).

       $INVOCATION_ID
           Contains a randomized, unique 128bit ID identifying each runtime
           cycle of the unit, formatted as 32 character hexadecimal string. A
           new ID is assigned each time the unit changes from an inactive
           state into an activating or active state, and may be used to
           identify this specific runtime cycle, in particular in data stored
           offline, such as the journal. The same ID is passed to all
           processes run as part of the unit.

       $XDG_RUNTIME_DIR
           The directory to use for runtime objects (such as IPC objects) and
           volatile state. Set for all services run by the user systemd
           instance, as well as any system services that use PAMName= with a
           PAM stack that includes pam_systemd. See below and pam_systemd(8)
           for more information.

       $RUNTIME_DIRECTORY, $STATE_DIRECTORY, $CACHE_DIRECTORY,
       $LOGS_DIRECTORY, $CONFIGURATION_DIRECTORY
           Contains and absolute paths to the directories defined with
           RuntimeDirectory=, StateDirectory=, CacheDirectory=,
           LogsDirectory=, and ConfigurationDirectory= when those settings are
           used.

       $MAINPID
           The PID of the unit's main process if it is known. This is only set
           for control processes as invoked by ExecReload= and similar.

       $MANAGERPID
           The PID of the user systemd instance, set for processes spawned by
           it.

       $LISTEN_FDS, $LISTEN_PID, $LISTEN_FDNAMES
           Information about file descriptors passed to a service for socket
           activation. See sd_listen_fds(3).

       $NOTIFY_SOCKET
           The socket sd_notify() talks to. See sd_notify(3).

       $WATCHDOG_PID, $WATCHDOG_USEC
           Information about watchdog keep-alive notifications. See
           sd_watchdog_enabled(3).

       $TERM
           Terminal type, set only for units connected to a terminal
           (StandardInput=tty, StandardOutput=tty, or StandardError=tty). See
           termcap(5).

       $JOURNAL_STREAM
           If the standard output or standard error output of the executed
           processes are connected to the journal (for example, by setting
           StandardError=journal) $JOURNAL_STREAM contains the device and
           inode numbers of the connection file descriptor, formatted in
           decimal, separated by a colon (":"). This permits invoked processes
           to safely detect whether their standard output or standard error
           output are connected to the journal. The device and inode numbers
           of the file descriptors should be compared with the values set in
           the environment variable to determine whether the process output is
           still connected to the journal. Note that it is generally not
           sufficient to only check whether $JOURNAL_STREAM is set at all as
           services might invoke external processes replacing their standard
           output or standard error output, without unsetting the environment
           variable.

           If both standard output and standard error of the executed
           processes are connected to the journal via a stream socket, this
           environment variable will contain information about the standard
           error stream, as that's usually the preferred destination for log
           data. (Note that typically the same stream is used for both
           standard output and standard error, hence very likely the
           environment variable contains device and inode information matching
           both stream file descriptors.)

           This environment variable is primarily useful to allow services to
           optionally upgrade their used log protocol to the native journal
           protocol (using sd_journal_print(3) and other functions) if their
           standard output or standard error output is connected to the
           journal anyway, thus enabling delivery of structured metadata along
           with logged messages.

       $SERVICE_RESULT
           Only defined for the service unit type, this environment variable
           is passed to all ExecStop= and ExecStopPost= processes, and encodes
           the service "result". Currently, the following values are defined:

           Table 4. Defined $SERVICE_RESULT values
           +------------------+----------------------------+
           |Value             | Meaning                    |
           +------------------+----------------------------+
           |"success"         | The service ran            |
           |                  | successfully and exited    |
           |                  | cleanly.                   |
           +------------------+----------------------------+
           |"protocol"        | A protocol violation       |
           |                  | occurred: the service did  |
           |                  | not take the steps         |
           |                  | required by its unit       |
           |                  | configuration              |
           |                  | (specifically what is      |
           |                  | configured in its Type=    |
           |                  | setting).                  |
           +------------------+----------------------------+
           |"timeout"         | One of the steps timed     |
           |                  | out.                       |
           +------------------+----------------------------+
           |"exit-code"       | Service process exited     |
           |                  | with a non-zero exit code; |
           |                  | see $EXIT_CODE below for   |
           |                  | the actual exit code       |
           |                  | returned.                  |
           +------------------+----------------------------+
           |"signal"          | A service process was      |
           |                  | terminated abnormally by a |
           |                  | signal, without dumping    |
           |                  | core. See $EXIT_CODE below |
           |                  | for the actual signal      |
           |                  | causing the termination.   |
           +------------------+----------------------------+
           |"core-dump"       | A service process          |
           |                  | terminated abnormally with |
           |                  | a signal and dumped core.  |
           |                  | See $EXIT_CODE below for   |
           |                  | the signal causing the     |
           |                  | termination.               |
           +------------------+----------------------------+
           |"watchdog"        | Watchdog keep-alive ping   |
           |                  | was enabled for the        |
           |                  | service, but the deadline  |
           |                  | was missed.                |
           +------------------+----------------------------+
           |"start-limit-hit" | A start limit was defined  |
           |                  | for the unit and it was    |
           |                  | hit, causing the unit to   |
           |                  | fail to start. See         |
           |                  | systemd.unit(5)'s          |
           |                  | StartLimitIntervalSec= and |
           |                  | StartLimitBurst= for       |
           |                  | details.                   |
           +------------------+----------------------------+
           |"resources"       | A catch-all condition in   |
           |                  | case a system operation    |
           |                  | failed.                    |
           +------------------+----------------------------+
           This environment variable is useful to monitor failure or
           successful termination of a service. Even though this variable is
           available in both ExecStop= and ExecStopPost=, it is usually a
           better choice to place monitoring tools in the latter, as the
           former is only invoked for services that managed to start up
           correctly, and the latter covers both services that failed during
           their start-up and those which failed during their runtime.

       $EXIT_CODE, $EXIT_STATUS
           Only defined for the service unit type, these environment variables
           are passed to all ExecStop=, ExecStopPost= processes and contain
           exit status/code information of the main process of the service.
           For the precise definition of the exit code and status, see
           wait(2).  $EXIT_CODE is one of "exited", "killed", "dumped".
           $EXIT_STATUS contains the numeric exit code formatted as string if
           $EXIT_CODE is "exited", and the signal name in all other cases.
           Note that these environment variables are only set if the service
           manager succeeded to start and identify the main process of the
           service.

           Table 5. Summary of possible service result variable values
           +------------------+------------------+---------------------+
           |$SERVICE_RESULT   | $EXIT_CODE       | $EXIT_STATUS        |
           +------------------+------------------+---------------------+
           |"success"         | "killed"         | "HUP", "INT",       |
           |                  |                  | "TERM", "PIPE"      |
           |                  +------------------+---------------------+
           |                  | "exited"         | "0"                 |
           +------------------+------------------+---------------------+
           |"protocol"        | not set          | not set             |
           |                  +------------------+---------------------+
           |                  | "exited"         | "0"                 |
           +------------------+------------------+---------------------+
           |"timeout"         | "killed"         | "TERM", "KILL"      |
           |                  +------------------+---------------------+
           |                  | "exited"         | "0", "1", "2", "3", |
           |                  |                  | ..., "255"          |
           +------------------+------------------+---------------------+
           |"exit-code"       | "exited"         | "1", "2", "3", ..., |
           |                  |                  | "255"               |
           +------------------+------------------+---------------------+
           |"signal"          | "killed"         | "HUP", "INT",       |
           |                  |                  | "KILL", ...         |
           +------------------+------------------+---------------------+
           |"core-dump"       | "dumped"         | "ABRT", "SEGV",     |
           |                  |                  | "QUIT", ...         |
           +------------------+------------------+---------------------+
           |"watchdog"        | "dumped"         | "ABRT"              |
           |                  +------------------+---------------------+
           |                  | "killed"         | "TERM", "KILL"      |
           |                  +------------------+---------------------+
           |                  | "exited"         | "0", "1", "2", "3", |
           |                  |                  | ..., "255"          |
           +------------------+------------------+---------------------+
           |"exec-condition"  | "exited"         | "1", "2", "3", "4", |
           |                  |                  | ..., "254"          |
           +------------------+------------------+---------------------+
           |"oom-kill"        | "killed"         | "TERM", "KILL"      |
           +------------------+------------------+---------------------+
           |"start-limit-hit" | not set          | not set             |
           +------------------+------------------+---------------------+
           |"resources"       | any of the above | any of the above    |
           +------------------+------------------+---------------------+
           |Note: the process may be also terminated by a signal not   |
           |sent by systemd. In particular the process may send an     |
           |arbitrary signal to itself in a handler for any of the     |
           |non-maskable signals. Nevertheless, in the "timeout" and   |
           |"watchdog" rows above only the signals that systemd sends  |
           |have been included. Moreover, using SuccessExitStatus=     |
           |additional exit statuses may be declared to indicate clean |
           |termination, which is not reflected by this table.         |
           +-----------------------------------------------------------+

       $PIDFILE
           The path to the configured PID file, in case the process is forked
           off on behalf of a service that uses the PIDFile= setting, see
           systemd.service(5) for details. Service code may use this
           environment variable to automatically generate a PID file at the
           location configured in the unit file. This field is set to an
           absolute path in the file system.

       For system services, when PAMName= is enabled and pam_systemd is part
       of the selected PAM stack, additional environment variables defined by
       systemd may be set for services. Specifically, these are $XDG_SEAT,
       $XDG_VTNR, see pam_systemd(8) for details.

PROCESS EXIT CODES
       When invoking a unit process the service manager possibly fails to
       apply the execution parameters configured with the settings above. In
       that case the already created service process will exit with a non-zero
       exit code before the configured command line is executed. (Or in other
       words, the child process possibly exits with these error codes, after
       having been created by the fork(2) system call, but before the matching
       execve(2) system call is called.) Specifically, exit codes defined by
       the C library, by the LSB specification and by the systemd service
       manager itself are used.

       The following basic service exit codes are defined by the C library.

       Table 6. Basic C library exit codes
       +----------+---------------+--------------------+
       |Exit Code | Symbolic Name | Description        |
       +----------+---------------+--------------------+
       |0         | EXIT_SUCCESS  | Generic success    |
       |          |               | code.              |
       +----------+---------------+--------------------+
       |1         | EXIT_FAILURE  | Generic failure or |
       |          |               | unspecified error. |
       +----------+---------------+--------------------+

       The following service exit codes are defined by the LSB
       specification[8].

       Table 7. LSB service exit codes
       +----------+----------------------+--------------------+
       |Exit Code | Symbolic Name        | Description        |
       +----------+----------------------+--------------------+
       |2         | EXIT_INVALIDARGUMENT | Invalid or excess  |
       |          |                      | arguments.         |
       +----------+----------------------+--------------------+
       |3         | EXIT_NOTIMPLEMENTED  | Unimplemented      |
       |          |                      | feature.           |
       +----------+----------------------+--------------------+
       |4         | EXIT_NOPERMISSION    | The user has       |
       |          |                      | insufficient       |
       |          |                      | privileges.        |
       +----------+----------------------+--------------------+
       |5         | EXIT_NOTINSTALLED    | The program is not |
       |          |                      | installed.         |
       +----------+----------------------+--------------------+
       |6         | EXIT_NOTCONFIGURED   | The program is not |
       |          |                      | configured.        |
       +----------+----------------------+--------------------+
       |7         | EXIT_NOTRUNNING      | The program is not |
       |          |                      | running.           |
       +----------+----------------------+--------------------+

       The LSB specification suggests that error codes 200 and above are
       reserved for implementations. Some of them are used by the service
       manager to indicate problems during process invocation:

       Table 8. systemd-specific exit codes
       +----------+------------------------------+---------------------------------------------+
       |Exit Code | Symbolic Name                | Description                                 |
       +----------+------------------------------+---------------------------------------------+
       |200       | EXIT_CHDIR                   | Changing to the                             |
       |          |                              | requested working                           |
       |          |                              | directory failed.                           |
       |          |                              | See                                         |
       |          |                              | WorkingDirectory=                           |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |201       | EXIT_NICE                    | Failed to set up                            |
       |          |                              | process scheduling                          |
       |          |                              | priority (nice                              |
       |          |                              | level). See Nice=                           |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |202       | EXIT_FDS                     | Failed to close                             |
       |          |                              | unwanted file                               |
       |          |                              | descriptors, or to                          |
       |          |                              | adjust passed file                          |
       |          |                              | descriptors.                                |
       +----------+------------------------------+---------------------------------------------+
       |203       | EXIT_EXEC                    | The actual process                          |
       |          |                              | execution failed                            |
       |          |                              | (specifically, the                          |
       |          |                              | execve(2) system                            |
       |          |                              | call). Most likely                          |
       |          |                              | this is caused by a                         |
       |          |                              | missing or                                  |
       |          |                              | non-accessible                              |
       |          |                              | executable file.                            |
       +----------+------------------------------+---------------------------------------------+
       |204       | EXIT_MEMORY                  | Failed to perform                           |
       |          |                              | an action due to                            |
       |          |                              | memory shortage.                            |
       +----------+------------------------------+---------------------------------------------+
       |205       | EXIT_LIMITS                  | Failed to adjust                            |
       |          |                              | resource limits.                            |
       |          |                              | See LimitCPU= and                           |
       |          |                              | related settings                            |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |206       | EXIT_OOM_ADJUST              | Failed to adjust                            |
       |          |                              | the OOM setting.                            |
       |          |                              | See OOMScoreAdjust=                         |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |207       | EXIT_SIGNAL_MASK             | Failed to set                               |
       |          |                              | process signal                              |
       |          |                              | mask.                                       |
       +----------+------------------------------+---------------------------------------------+
       |208       | EXIT_STDIN                   | Failed to set up                            |
       |          |                              | standard input. See                         |
       |          |                              | StandardInput=                              |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |209       | EXIT_STDOUT                  | Failed to set up                            |
       |          |                              | standard output.                            |
       |          |                              | See StandardOutput=                         |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |210       | EXIT_CHROOT                  | Failed to change                            |
       |          |                              | root directory                              |
       |          |                              | (chroot(2)). See                            |
       |          |                              | RootDirectory=/RootImage=                   |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |211       | EXIT_IOPRIO                  | Failed to set up IO                         |
       |          |                              | scheduling priority. See                    |
       |          |                              | IOSchedulingClass=/IOSchedulingPriority=    |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |212       | EXIT_TIMERSLACK              | Failed to set up timer slack. See           |
       |          |                              | TimerSlackNSec= above.                      |
       +----------+------------------------------+---------------------------------------------+
       |213       | EXIT_SECUREBITS              | Failed to set process secure bits. See      |
       |          |                              | SecureBits= above.                          |
       +----------+------------------------------+---------------------------------------------+
       |214       | EXIT_SETSCHEDULER            | Failed to set up CPU scheduling. See        |
       |          |                              | CPUSchedulingPolicy=/CPUSchedulingPriority= |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |215       | EXIT_CPUAFFINITY             | Failed to set up CPU affinity. See          |
       |          |                              | CPUAffinity= above.                         |
       +----------+------------------------------+---------------------------------------------+
       |216       | EXIT_GROUP                   | Failed to determine or change group         |
       |          |                              | credentials. See                            |
       |          |                              | Group=/SupplementaryGroups= above.          |
       +----------+------------------------------+---------------------------------------------+
       |217       | EXIT_USER                    | Failed to determine or change user          |
       |          |                              | credentials, or to set up user namespacing. |
       |          |                              | See User=/PrivateUsers= above.              |
       +----------+------------------------------+---------------------------------------------+
       |218       | EXIT_CAPABILITIES            | Failed to drop capabilities, or apply       |
       |          |                              | ambient capabilities. See                   |
       |          |                              | CapabilityBoundingSet=/AmbientCapabilities= |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |219       | EXIT_CGROUP                  | Setting up the service control group        |
       |          |                              | failed.                                     |
       +----------+------------------------------+---------------------------------------------+
       |220       | EXIT_SETSID                  | Failed to create new process session.       |
       +----------+------------------------------+---------------------------------------------+
       |221       | EXIT_CONFIRM                 | Execution has been cancelled by the user.   |
       |          |                              | See the systemd.confirm_spawn= kernel       |
       |          |                              | command line setting on kernel-command-     |
       |          |                              | line(7) for details.                        |
       +----------+------------------------------+---------------------------------------------+
       |222       | EXIT_STDERR                  | Failed to set up standard error output. See |
       |          |                              | StandardError= above.                       |
       +----------+------------------------------+---------------------------------------------+
       |224       | EXIT_PAM                     | Failed to set up PAM session. See PAMName=  |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |225       | EXIT_NETWORK                 | Failed to set up network namespacing. See   |
       |          |                              | PrivateNetwork= above.                      |
       +----------+------------------------------+---------------------------------------------+
       |226       | EXIT_NAMESPACE               | Failed to set up mount namespacing. See     |
       |          |                              | ReadOnlyPaths= and related settings above.  |
       +----------+------------------------------+---------------------------------------------+
       |227       | EXIT_NO_NEW_PRIVILEGES       | Failed to disable new privileges. See       |
       |          |                              | NoNewPrivileges=yes above.                  |
       +----------+------------------------------+---------------------------------------------+
       |228       | EXIT_SECCOMP                 | Failed to apply system call filters. See    |
       |          |                              | SystemCallFilter= and related settings      |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |229       | EXIT_SELINUX_CONTEXT         | Determining or changing SELinux context     |
       |          |                              | failed. See SELinuxContext= above.          |
       +----------+------------------------------+---------------------------------------------+
       |230       | EXIT_PERSONALITY             | Failed to set up an execution domain        |
       |          |                              | (personality). See Personality= above.      |
       +----------+------------------------------+---------------------------------------------+
       |231       | EXIT_APPARMOR_PROFILE        | Failed to prepare changing AppArmor         |
       |          |                              | profile. See AppArmorProfile= above.        |
       +----------+------------------------------+---------------------------------------------+
       |232       | EXIT_ADDRESS_FAMILIES        | Failed to restrict address families. See    |
       |          |                              | RestrictAddressFamilies= above.             |
       +----------+------------------------------+---------------------------------------------+
       |233       | EXIT_RUNTIME_DIRECTORY       | Setting up runtime directory failed. See    |
       |          |                              | RuntimeDirectory= and related settings      |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |235       | EXIT_CHOWN                   | Failed to adjust socket ownership. Used for |
       |          |                              | socket units only.                          |
       +----------+------------------------------+---------------------------------------------+
       |236       | EXIT_SMACK_PROCESS_LABEL     | Failed to set SMACK label. See              |
       |          |                              | SmackProcessLabel= above.                   |
       +----------+------------------------------+---------------------------------------------+
       |237       | EXIT_KEYRING                 | Failed to set up kernel keyring.            |
       +----------+------------------------------+---------------------------------------------+
       |238       | EXIT_STATE_DIRECTORY         | Failed to set up unit's state directory.    |
       |          |                              | See StateDirectory= above.                  |
       +----------+------------------------------+---------------------------------------------+
       |239       | EXIT_CACHE_DIRECTORY         | Failed to set up unit's cache directory.    |
       |          |                              | See CacheDirectory= above.                  |
       +----------+------------------------------+---------------------------------------------+
       |240       | EXIT_LOGS_DIRECTORY          | Failed to set up unit's logging directory.  |
       |          |                              | See LogsDirectory= above.                   |
       +----------+------------------------------+---------------------------------------------+
       |241       | EXIT_CONFIGURATION_DIRECTORY | Failed to set up unit's configuration       |
       |          |                              | directory. See ConfigurationDirectory=      |
       |          |                              | above.                                      |
       +----------+------------------------------+---------------------------------------------+
       |242       | EXIT_NUMA_POLICY             | Failed to set up unit's NUMA memory policy. |
       |          |                              | See NUMAPolicy= and NUMAMask=above.         |
       +----------+------------------------------+---------------------------------------------+

       Finally, the BSD operating systems define a set of exit codes,
       typically defined on Linux systems too:

       Table 9. BSD exit codes
       +----------+----------------+---------------------+
       |Exit Code | Symbolic Name  | Description         |
       +----------+----------------+---------------------+
       |64        | EX_USAGE       | Command line usage  |
       |          |                | error               |
       +----------+----------------+---------------------+
       |65        | EX_DATAERR     | Data format error   |
       +----------+----------------+---------------------+
       |66        | EX_NOINPUT     | Cannot open input   |
       +----------+----------------+---------------------+
       |67        | EX_NOUSER      | Addressee unknown   |
       +----------+----------------+---------------------+
       |68        | EX_NOHOST      | Host name unknown   |
       +----------+----------------+---------------------+
       |69        | EX_UNAVAILABLE | Service unavailable |
       +----------+----------------+---------------------+
       |70        | EX_SOFTWARE    | internal software   |
       |          |                | error               |
       +----------+----------------+---------------------+
       |71        | EX_OSERR       | System error (e.g., |
       |          |                | can't fork)         |
       +----------+----------------+---------------------+
       |72        | EX_OSFILE      | Critical OS file    |
       |          |                | missing             |
       +----------+----------------+---------------------+
       |73        | EX_CANTCREAT   | Can't create (user) |
       |          |                | output file         |
       +----------+----------------+---------------------+
       |74        | EX_IOERR       | Input/output error  |
       +----------+----------------+---------------------+
       |75        | EX_TEMPFAIL    | Temporary failure;  |
       |          |                | user is invited to  |
       |          |                | retry               |
       +----------+----------------+---------------------+
       |76        | EX_PROTOCOL    | Remote error in     |
       |          |                | protocol            |
       +----------+----------------+---------------------+
       |77        | EX_NOPERM      | Permission denied   |
       +----------+----------------+---------------------+
       |78        | EX_CONFIG      | Configuration error |
       +----------+----------------+---------------------+

SEE ALSO
       systemd(1), systemctl(1), systemd-analyze(1), journalctl(1), systemd-
       system.conf(5), systemd.unit(5), systemd.service(5), systemd.socket(5),
       systemd.swap(5), systemd.mount(5), systemd.kill(5), systemd.resource-
       control(5), systemd.time(7), systemd.directives(7), tmpfiles.d(5),
       exec(3)

NOTES
        1. Discoverable Partitions Specification
           https://systemd.io/DISCOVERABLE_PARTITIONS

        2. User/Group Name Syntax
           https://systemd.io/USER_NAMES

        3. No New Privileges Flag
           https://www.kernel.org/doc/html/latest/userspace-api/no_new_privs.html

        4. proc.txt
           https://www.kernel.org/doc/Documentation/filesystems/proc.txt

        5. C escapes
           https://en.wikipedia.org/wiki/Escape_sequences_in_C#Table_of_escape_sequences

        6. most control characters
           https://en.wikipedia.org/wiki/Control_character#In_ASCII

        7. Base64
           https://tools.ietf.org/html/rfc2045#section-6.8

        8. LSB specification
           https://refspecs.linuxbase.org/LSB_5.0.0/LSB-Core-generic/LSB-Core-generic/iniscrptact.html

systemd 245                                                    SYSTEMD.EXEC(5)

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