apt.conf(5)



APT.CONF(5)                           APT                          APT.CONF(5)

NAME
       apt.conf - Configuration file for APT

DESCRIPTION
       /etc/apt/apt.conf is the main configuration file shared by all the
       tools in the APT suite of tools, though it is by no means the only
       place options can be set. The suite also shares a common command line
       parser to provide a uniform environment.

       When an APT tool starts up it will read the configuration files in the
       following order:

        1. the file specified by the APT_CONFIG environment variable (if any)

        2. all files in Dir::Etc::Parts in alphanumeric ascending order which
           have either no or "conf" as filename extension and which only
           contain alphanumeric, hyphen (-), underscore (_) and period (.)
           characters. Otherwise APT will print a notice that it has ignored a
           file, unless that file matches a pattern in the
           Dir::Ignore-Files-Silently configuration list - in which case it
           will be silently ignored.

        3. the main configuration file specified by Dir::Etc::main

        4. all options set in the binary specific configuration subtree are
           moved into the root of the tree.

        5. the command line options are applied to override the configuration
           directives or to load even more configuration files.

SYNTAX
       The configuration file is organized in a tree with options organized
       into functional groups. Option specification is given with a double
       colon notation; for instance APT::Get::Assume-Yes is an option within
       the APT tool group, for the Get tool. Options do not inherit from their
       parent groups.

       Syntactically the configuration language is modeled after what the ISC
       tools such as bind and dhcp use. Lines starting with // are treated as
       comments (ignored), as well as all text between /* and */, just like
       C/C++ comments. Each line is of the form APT::Get::Assume-Yes "true";.
       The quotation marks and trailing semicolon are required. The value must
       be on one line, and there is no kind of string concatenation. Values
       must not include backslashes or extra quotation marks. Option names are
       made up of alphanumeric characters and the characters "/-:._+". A new
       scope can be opened with curly braces, like this:

           APT {
             Get {
               Assume-Yes "true";
               Fix-Broken "true";
             };
           };

       with newlines placed to make it more readable. Lists can be created by
       opening a scope and including a single string enclosed in quotes
       followed by a semicolon. Multiple entries can be included, separated by
       a semicolon.

           DPkg::Pre-Install-Pkgs {"/usr/sbin/dpkg-preconfigure --apt";};

       In general the sample configuration file
       /usr/share/doc/apt/examples/configure-index.gz is a good guide for how
       it should look.

       Case is not significant in names of configuration items, so in the
       previous example you could use dpkg::pre-install-pkgs.

       Names for the configuration items are optional if a list is defined as
       can be seen in the DPkg::Pre-Install-Pkgs example above. If you don't
       specify a name a new entry will simply add a new option to the list. If
       you specify a name you can override the option in the same way as any
       other option by reassigning a new value to the option.

       Two special commands are defined: #include (which is deprecated and not
       supported by alternative implementations) and #clear.  #include will
       include the given file, unless the filename ends in a slash, in which
       case the whole directory is included.  #clear is used to erase a part
       of the configuration tree. The specified element and all its
       descendants are erased. (Note that these lines also need to end with a
       semicolon.)

       The #clear command is the only way to delete a list or a complete
       scope. Reopening a scope (or using the syntax described below with an
       appended ::) will not override previously written entries. Options can
       only be overridden by addressing a new value to them - lists and scopes
       can't be overridden, only cleared.

       All of the APT tools take an -o option which allows an arbitrary
       configuration directive to be specified on the command line. The syntax
       is a full option name (APT::Get::Assume-Yes for instance) followed by
       an equals sign then the new value of the option. To append a new
       element to a list, add a trailing :: to the name of the list. (As you
       might suspect, the scope syntax can't be used on the command line.)

       Note that appending items to a list using :: only works for one item
       per line, and that you should not use it in combination with the scope
       syntax (which adds :: implicitly). Using both syntaxes together will
       trigger a bug which some users unfortunately depend on: an option with
       the unusual name "::" which acts like every other option with a name.
       This introduces many problems; for one thing, users who write multiple
       lines in this wrong syntax in the hope of appending to a list will
       achieve the opposite, as only the last assignment for this option "::"
       will be used. Future versions of APT will raise errors and stop working
       if they encounter this misuse, so please correct such statements now
       while APT doesn't explicitly complain about them.

THE APT GROUP
       This group of options controls general APT behavior as well as holding
       the options for all of the tools.

       Architecture
           System Architecture; sets the architecture to use when fetching
           files and parsing package lists. The internal default is the
           architecture apt was compiled for.

       Architectures
           All Architectures the system supports. For instance, CPUs
           implementing the amd64 (also called x86-64) instruction set are
           also able to execute binaries compiled for the i386 (x86)
           instruction set. This list is used when fetching files and parsing
           package lists. The initial default is always the system's native
           architecture (APT::Architecture), and foreign architectures are
           added to the default list when they are registered via dpkg
           --add-architecture.

       Compressor
           This scope defines which compression formats are supported, how
           compression and decompression can be performed if support for this
           format isn't built into apt directly and a cost-value indicating
           how costly it is to compress something in this format. As an
           example the following configuration stanza would allow apt to
           download and uncompress as well as create and store files with the
           low-cost .reversed file extension which it will pass to the command
           rev without additional commandline parameters for compression and
           uncompression:

               APT::Compressor::rev {
                    Name "rev";
                    Extension ".reversed";
                    Binary "rev";
                    CompressArg {};
                    UncompressArg {};
                    Cost "10";
               };

       Build-Profiles
           List of all build profiles enabled for build-dependency resolution,
           without the "profile." namespace prefix. By default this list is
           empty. The DEB_BUILD_PROFILES as used by dpkg-buildpackage(1)
           overrides the list notation.

       Default-Release
           Default release to install packages from if more than one version
           is available. Contains release name, codename or release version.
           Examples: 'stable', 'testing', 'unstable', 'buster', 'bullseye',
           '4.0', '5.0*'. See also apt_preferences(5).

       Ignore-Hold
           Ignore held packages; this global option causes the problem
           resolver to ignore held packages in its decision making.

       Clean-Installed
           Defaults to on. When turned on the autoclean feature will remove
           any packages which can no longer be downloaded from the cache. If
           turned off then packages that are locally installed are also
           excluded from cleaning - but note that APT provides no direct means
           to reinstall them.

       Immediate-Configure
           Defaults to on, which will cause APT to install essential and
           important packages as soon as possible in an install/upgrade
           operation, in order to limit the effect of a failing dpkg(1) call.
           If this option is disabled, APT treats an important package in the
           same way as an extra package: between the unpacking of the package
           A and its configuration there can be many other unpack or
           configuration calls for other unrelated packages B, C etc. If these
           cause the dpkg(1) call to fail (e.g. because package B's maintainer
           scripts generate an error), this results in a system state in which
           package A is unpacked but unconfigured - so any package depending
           on A is now no longer guaranteed to work, as its dependency on A is
           no longer satisfied.

           The immediate configuration marker is also applied in the
           potentially problematic case of circular dependencies, since a
           dependency with the immediate flag is equivalent to a
           Pre-Dependency. In theory this allows APT to recognise a situation
           in which it is unable to perform immediate configuration, abort,
           and suggest to the user that the option should be temporarily
           deactivated in order to allow the operation to proceed. Note the
           use of the word "theory" here; in the real world this problem has
           rarely been encountered, in non-stable distribution versions, and
           was caused by wrong dependencies of the package in question or by a
           system in an already broken state; so you should not blindly
           disable this option, as the scenario mentioned above is not the
           only problem it can help to prevent in the first place.

           Before a big operation like dist-upgrade is run with this option
           disabled you should try to explicitly install the package APT is
           unable to configure immediately; but please make sure you also
           report your problem to your distribution and to the APT team with
           the buglink below, so they can work on improving or correcting the
           upgrade process.

       Force-LoopBreak
           Never enable this option unless you really know what you are doing.
           It permits APT to temporarily remove an essential package to break
           a Conflicts/Conflicts or Conflicts/Pre-Depends loop between two
           essential packages.  Such a loop should never exist and is a grave
           bug. This option will work if the essential packages are not tar,
           gzip, libc, dpkg, dash or anything that those packages depend on.

       Cache-Start, Cache-Grow, Cache-Limit
           APT uses since version 0.7.26 a resizable memory mapped cache file
           to store the available information.  Cache-Start acts as a hint of
           the size the cache will grow to, and is therefore the amount of
           memory APT will request at startup. The default value is 20971520
           bytes (~20 MB). Note that this amount of space needs to be
           available for APT; otherwise it will likely fail ungracefully, so
           for memory restricted devices this value should be lowered while on
           systems with a lot of configured sources it should be increased.
           Cache-Grow defines in bytes with the default of 1048576 (~1 MB) how
           much the cache size will be increased in the event the space
           defined by Cache-Start is not enough. This value will be applied
           again and again until either the cache is big enough to store all
           information or the size of the cache reaches the Cache-Limit. The
           default of Cache-Limit is 0 which stands for no limit. If
           Cache-Grow is set to 0 the automatic growth of the cache is
           disabled.

       Build-Essential
           Defines which packages are considered essential build dependencies.

       Get
           The Get subsection controls the apt-get(8) tool; please see its
           documentation for more information about the options here.

       Cache
           The Cache subsection controls the apt-cache(8) tool; please see its
           documentation for more information about the options here.

       CDROM
           The CDROM subsection controls the apt-cdrom(8) tool; please see its
           documentation for more information about the options here.

THE ACQUIRE GROUP
       The Acquire group of options controls the download of packages as well
       as the various "acquire methods" responsible for the download itself
       (see also sources.list(5)).

       Check-Date
           Security related option defaulting to true, enabling time-related
           checks. Disabling it means that the machine's time cannot be
           trusted, and APT will hence disable all time-related checks, such
           as Check-Valid-Until and verifying that the Date field of a release
           file is not in the future.

       Max-FutureTime
           Maximum time (in seconds) before its creation (as indicated by the
           Date header) that the Release file should be considered valid. The
           default value is 10. Archive specific settings can be made by
           appending the label of the archive to the option name. Preferably,
           the same can be achieved for specific sources.list(5) entries by
           using the Date-Max-Future option there.

       Check-Valid-Until
           Security related option defaulting to true, as giving a Release
           file's validation an expiration date prevents replay attacks over a
           long timescale, and can also for example help users to identify
           mirrors that are no longer updated - but the feature depends on the
           correctness of the clock on the user system. Archive maintainers
           are encouraged to create Release files with the Valid-Until header,
           but if they don't or a stricter value is desired the Max-ValidTime
           option below can be used. The Check-Valid-Until option of
           sources.list(5) entries should be preferred to disable the check
           selectively instead of using this global override.

       Max-ValidTime
           Maximum time (in seconds) after its creation (as indicated by the
           Date header) that the Release file should be considered valid. If
           the Release file itself includes a Valid-Until header the earlier
           date of the two is used as the expiration date. The default value
           is 0 which stands for "valid forever". Archive specific settings
           can be made by appending the label of the archive to the option
           name. Preferably, the same can be achieved for specific
           sources.list(5) entries by using the Valid-Until-Max option there.

       Min-ValidTime
           Minimum time (in seconds) after its creation (as indicated by the
           Date header) that the Release file should be considered valid. Use
           this if you need to use a seldom updated (local) mirror of a more
           frequently updated archive with a Valid-Until header instead of
           completely disabling the expiration date checking. Archive specific
           settings can and should be used by appending the label of the
           archive to the option name. Preferably, the same can be achieved
           for specific sources.list(5) entries by using the Valid-Until-Min
           option there.

       AllowTLS
           Allow use of the internal TLS support in the http method. If set to
           false, this completely disables support for TLS in apt's own
           methods (excluding the curl-based https method). No TLS-related
           functions will be called anymore.

       PDiffs
           Try to download deltas called PDiffs for indexes (like Packages
           files) instead of downloading whole ones. True by default.
           Preferably, this can be set for specific sources.list(5) entries or
           index files by using the PDiffs option there.

           Two sub-options to limit the use of PDiffs are also available:
           FileLimit can be used to specify a maximum number of PDiff files
           should be downloaded to update a file.  SizeLimit on the other hand
           is the maximum percentage of the size of all patches compared to
           the size of the targeted file. If one of these limits is exceeded
           the complete file is downloaded instead of the patches.

       By-Hash
           Try to download indexes via an URI constructed from a hashsum of
           the expected file rather than downloaded via a well-known stable
           filename. True by default, but automatically disabled if the source
           indicates no support for it. Usage can be forced with the special
           value "force". Preferably, this can be set for specific
           sources.list(5) entries or index files by using the By-Hash option
           there.

       Queue-Mode
           Queuing mode; Queue-Mode can be one of host or access which
           determines how APT parallelizes outgoing connections.  host means
           that one connection per target host will be opened, access means
           that one connection per URI type will be opened.

       Retries
           Number of retries to perform. If this is non-zero APT will retry
           failed files the given number of times.

       Source-Symlinks
           Use symlinks for source archives. If set to true then source
           archives will be symlinked when possible instead of copying. True
           is the default.

       http https
           The options in these scopes configure APTs acquire transports for
           the protocols HTTP and HTTPS and are documented in the apt-
           transport-http(1) and apt-transport-https(1) manpages respectively.

       ftp
           ftp::Proxy sets the default proxy to use for FTP URIs. It is in the
           standard form of ftp://[[user][:pass]@]host[:port]/. Per host
           proxies can also be specified by using the form ftp::Proxy::<host>
           with the special keyword DIRECT meaning to use no proxies. If no
           one of the above settings is specified, ftp_proxy environment
           variable will be used. To use an FTP proxy you will have to set the
           ftp::ProxyLogin script in the configuration file. This entry
           specifies the commands to send to tell the proxy server what to
           connect to. Please see
           /usr/share/doc/apt/examples/configure-index.gz for an example of
           how to do this. The substitution variables representing the
           corresponding URI component are $(PROXY_USER), $(PROXY_PASS),
           $(SITE_USER), $(SITE_PASS), $(SITE) and $(SITE_PORT).

           The option timeout sets the timeout timer used by the method; this
           value applies to the connection as well as the data timeout.

           Several settings are provided to control passive mode. Generally it
           is safe to leave passive mode on; it works in nearly every
           environment. However, some situations require that passive mode be
           disabled and port mode FTP used instead. This can be done globally
           or for connections that go through a proxy or for a specific host
           (see the sample config file for examples).

           It is possible to proxy FTP over HTTP by setting the ftp_proxy
           environment variable to an HTTP URL - see the discussion of the
           http method above for syntax. You cannot set this in the
           configuration file and it is not recommended to use FTP over HTTP
           due to its low efficiency.

           The setting ForceExtended controls the use of RFC2428 EPSV and EPRT
           commands. The default is false, which means these commands are only
           used if the control connection is IPv6. Setting this to true forces
           their use even on IPv4 connections. Note that most FTP servers do
           not support RFC2428.

       cdrom
           For URIs using the cdrom method, the only configurable option is
           the mount point, cdrom::Mount, which must be the mount point for
           the CD-ROM (or DVD, or whatever) drive as specified in /etc/fstab.
           It is possible to provide alternate mount and unmount commands if
           your mount point cannot be listed in the fstab. The syntax is to
           put

               /cdrom/::Mount "foo";

           within the cdrom block. It is important to have the trailing slash.
           Unmount commands can be specified using UMount.

       gpgv
           For GPGV URIs the only configurable option is gpgv::Options, which
           passes additional parameters to gpgv.

       CompressionTypes
           List of compression types which are understood by the acquire
           methods. Files like Packages can be available in various
           compression formats. By default the acquire methods can decompress
           and recompress many common formats like xz and gzip; with this
           scope the supported formats can be queried, modified as well as
           support for more formats added (see also APT::Compressor). The
           syntax for this is:

               Acquire::CompressionTypes::FileExtension "Methodname";

           Also, the Order subgroup can be used to define in which order the
           acquire system will try to download the compressed files. The
           acquire system will try the first and proceed with the next
           compression type in this list on error, so to prefer one over the
           other type simply add the preferred type first - types not already
           added will be implicitly appended to the end of the list, so e.g.

               Acquire::CompressionTypes::Order:: "gz";

           can be used to prefer gzip compressed files over all other
           compression formats. If xz should be preferred over gzip and bzip2
           the configure setting should look like this:

               Acquire::CompressionTypes::Order { "xz"; "gz"; };

           It is not needed to add bz2 to the list explicitly as it will be
           added automatically.

           Note that the Dir::Bin::Methodname will be checked at run time. If
           this option has been set and support for this format isn't directly
           built into apt, the method will only be used if this file exists;
           e.g. for the bzip2 method (the inbuilt) setting is:

               Dir::Bin::bzip2 "/bin/bzip2";

           Note also that list entries specified on the command line will be
           added at the end of the list specified in the configuration files,
           but before the default entries. To prefer a type in this case over
           the ones specified in the configuration files you can set the
           option direct - not in list style. This will not override the
           defined list; it will only prefix the list with this type.

           The special type uncompressed can be used to give uncompressed
           files a preference, but note that most archives don't provide
           uncompressed files so this is mostly only usable for local mirrors.

       GzipIndexes
           When downloading gzip compressed indexes (Packages, Sources, or
           Translations), keep them gzip compressed locally instead of
           unpacking them. This saves quite a lot of disk space at the expense
           of more CPU requirements when building the local package caches.
           False by default.

       Languages
           The Languages subsection controls which Translation files are
           downloaded and in which order APT tries to display the
           description-translations. APT will try to display the first
           available description in the language which is listed first.
           Languages can be defined with their short or long language codes.
           Note that not all archives provide Translation files for every
           language - the long language codes are especially rare.

           The default list includes "environment" and "en". "environment" has
           a special meaning here: it will be replaced at runtime with the
           language codes extracted from the LC_MESSAGES environment variable.
           It will also ensure that these codes are not included twice in the
           list. If LC_MESSAGES is set to "C" only the Translation-en file (if
           available) will be used. To force APT to use no Translation file
           use the setting Acquire::Languages=none. "none" is another special
           meaning code which will stop the search for a suitable Translation
           file. This tells APT to download these translations too, without
           actually using them unless the environment specifies the languages.
           So the following example configuration will result in the order
           "en, de" in an English locale or "de, en" in a German one. Note
           that "fr" is downloaded, but not used unless APT is used in a
           French locale (where the order would be "fr, de, en").

               Acquire::Languages { "environment"; "de"; "en"; "none"; "fr"; };

           Note: To prevent problems resulting from APT being executed in
           different environments (e.g. by different users or by other
           programs) all Translation files which are found in
           /var/lib/apt/lists/ will be added to the end of the list (after an
           implicit "none").

       ForceIPv4
           When downloading, force to use only the IPv4 protocol.

       ForceIPv6
           When downloading, force to use only the IPv6 protocol.

       MaxReleaseFileSize
           The maximum file size of Release/Release.gpg/InRelease files. The
           default is 10MB.

       EnableSrvRecords
           This option controls if apt will use the DNS SRV server record as
           specified in RFC 2782 to select an alternative server to connect
           to. The default is "true".

       AllowInsecureRepositories
           Allow update operations to load data files from repositories
           without sufficient security information. The default value is
           "false". Concept, implications as well as alternatives are detailed
           in apt-secure(8).

       AllowWeakRepositories
           Allow update operations to load data files from repositories which
           provide security information, but these are deemed no longer
           cryptographically strong enough. The default value is "false".
           Concept, implications as well as alternatives are detailed in apt-
           secure(8).

       AllowDowngradeToInsecureRepositories
           Allow that a repository that was previously gpg signed to become
           unsigned during an update operation. When there is no valid
           signature for a previously trusted repository apt will refuse the
           update. This option can be used to override this protection. You
           almost certainly never want to enable this. The default is false.
           Concept, implications as well as alternatives are detailed in apt-
           secure(8).

       Changelogs::URI scope
           Acquiring changelogs can only be done if an URI is known from where
           to get them. Preferable the Release file indicates this in a
           'Changelogs' field. If this isn't available the Label/Origin field
           of the Release file is used to check if a
           Acquire::Changelogs::URI::Label::LABEL or
           Acquire::Changelogs::URI::Origin::ORIGIN option exists and if so
           this value is taken. The value in the Release file can be
           overridden with Acquire::Changelogs::URI::Override::Label::LABEL or
           Acquire::Changelogs::URI::Override::Origin::ORIGIN. The value
           should be a normal URI to a text file, except that package specific
           data is replaced with the placeholder @CHANGEPATH@. The value for
           it is: 1. if the package is from a component (e.g.  main) this is
           the first part otherwise it is omitted, 2. the first letter of
           source package name, except if the source package name starts with
           'lib' in which case it will be the first four letters. 3. The
           complete source package name. 4. the complete name again and 5. the
           source version. The first (if present), second, third and fourth
           part are separated by a slash ('/') and between the fourth and
           fifth part is an underscore ('_'). The special value 'no' is
           available for this option indicating that this source can't be used
           to acquire changelog files from. Another source will be tried if
           available in this case.

BINARY SPECIFIC CONFIGURATION
       Especially with the introduction of the apt binary it can be useful to
       set certain options only for a specific binary as even options which
       look like they would effect only a certain binary like
       APT::Get::Show-Versions effect apt-get as well as apt.

       Setting an option for a specific binary only can be achieved by setting
       the option inside the Binary::specific-binary scope. Setting the option
       APT::Get::Show-Versions for the apt only can e.g. by done by setting
       Binary::apt::APT::Get::Show-Versions instead.

       Note that as seen in the DESCRIPTION section further above you can't
       set binary-specific options on the commandline itself nor in
       configuration files loaded via the commandline.

DIRECTORIES
       The Dir::State section has directories that pertain to local state
       information.  lists is the directory to place downloaded package lists
       in and status is the name of the dpkg(1) status file.  preferences is
       the name of the APT preferences file.  Dir::State contains the default
       directory to prefix on all sub-items if they do not start with / or ./.

       Dir::Cache contains locations pertaining to local cache information,
       such as the two package caches srcpkgcache and pkgcache as well as the
       location to place downloaded archives, Dir::Cache::archives. Generation
       of caches can be turned off by setting pkgcache or srcpkgcache to "".
       This will slow down startup but save disk space. It is probably
       preferable to turn off the pkgcache rather than the srcpkgcache. Like
       Dir::State the default directory is contained in Dir::Cache

       Dir::Etc contains the location of configuration files, sourcelist gives
       the location of the sourcelist and main is the default configuration
       file (setting has no effect, unless it is done from the config file
       specified by APT_CONFIG).

       The Dir::Parts setting reads in all the config fragments in lexical
       order from the directory specified. After this is done then the main
       config file is loaded.

       Binary programs are pointed to by Dir::Bin.  Dir::Bin::Methods
       specifies the location of the method handlers and gzip, bzip2, lzma,
       dpkg, apt-get dpkg-source dpkg-buildpackage and apt-cache specify the
       location of the respective programs.

       The configuration item RootDir has a special meaning. If set, all paths
       will be relative to RootDir, even paths that are specified absolutely.
       So, for instance, if RootDir is set to /tmp/staging and
       Dir::State::status is set to /var/lib/dpkg/status, then the status file
       will be looked up in /tmp/staging/var/lib/dpkg/status. If you want to
       prefix only relative paths, set Dir instead.

       The Ignore-Files-Silently list can be used to specify which files APT
       should silently ignore while parsing the files in the fragment
       directories. Per default a file which ends with .disabled, ~, .bak or
       .dpkg-[a-z]+ is silently ignored. As seen in the last default value
       these patterns can use regular expression syntax.

APT IN DSELECT
       When APT is used as a dselect(1) method several configuration
       directives control the default behavior. These are in the DSelect
       section.

       Clean
           Cache Clean mode; this value may be one of always, prompt, auto,
           pre-auto and never.  always and prompt will remove all packages
           from the cache after upgrading, prompt (the default) does so
           conditionally.  auto removes only those packages which are no
           longer downloadable (replaced with a new version for instance).
           pre-auto performs this action before downloading new packages.

       options
           The contents of this variable are passed to apt-get(8) as command
           line options when it is run for the install phase.

       Updateoptions
           The contents of this variable are passed to apt-get(8) as command
           line options when it is run for the update phase.

       PromptAfterUpdate
           If true the [U]pdate operation in dselect(1) will always prompt to
           continue. The default is to prompt only on error.

HOW APT CALLS DPKG(1)
       Several configuration directives control how APT invokes dpkg(1). These
       are in the DPkg section.

       options
           This is a list of options to pass to dpkg(1). The options must be
           specified using the list notation and each list item is passed as a
           single argument to dpkg(1).

       Path
           This is a string that defines the PATH environment variable used
           when running dpkg. It may be set to any valid value of that
           environment variable; or the empty string, in which case the
           variable is not changed.

       Pre-Invoke, Post-Invoke
           This is a list of shell commands to run before/after invoking
           dpkg(1). Like options this must be specified in list notation. The
           commands are invoked in order using /bin/sh; should any fail APT
           will abort.

       Pre-Install-Pkgs
           This is a list of shell commands to run before invoking dpkg(1).
           Like options this must be specified in list notation. The commands
           are invoked in order using /bin/sh; should any fail APT will abort.
           APT will pass the filenames of all .deb files it is going to
           install to the commands, one per line on the requested file
           descriptor, defaulting to standard input.

           Version 2 of this protocol sends more information through the
           requested file descriptor: a line with the text VERSION 2, the APT
           configuration space, and a list of package actions with filename
           and version information.

           Each configuration directive line has the form key=value. Special
           characters (equal signs, newlines, nonprintable characters,
           quotation marks, and percent signs in key and newlines,
           nonprintable characters, and percent signs in value) are %-encoded.
           Lists are represented by multiple key::=value lines with the same
           key. The configuration section ends with a blank line.

           Package action lines consist of five fields in Version 2: package
           name (without architecture qualification even if foreign), old
           version, direction of version change (< for upgrades, > for
           downgrades, = for no change), new version, action. The version
           fields are "-" for no version at all (for example when installing a
           package for the first time; no version is treated as earlier than
           any real version, so that is an upgrade, indicated as - < 1.23.4).
           The action field is "**CONFIGURE**" if the package is being
           configured, "**REMOVE**" if it is being removed, or the filename of
           a .deb file if it is being unpacked.

           In Version 3 after each version field follows the architecture of
           this version, which is "-" if there is no version, and a field
           showing the MultiArch type "same", "foreign", "allowed" or "none".
           Note that "none" is an incorrect typename which is just kept to
           remain compatible, it should be read as "no" and users are
           encouraged to support both.

           The version of the protocol to be used for the command cmd can be
           chosen by setting DPkg::Tools::options::cmd::Version accordingly,
           the default being version 1. If APT isn't supporting the requested
           version it will send the information in the highest version it has
           support for instead.

           The file descriptor to be used to send the information can be
           requested with DPkg::Tools::options::cmd::InfoFD which defaults to
           0 for standard input and is available since version 0.9.11. Support
           for the option can be detected by looking for the environment
           variable APT_HOOK_INFO_FD which contains the number of the used
           file descriptor as a confirmation.

       Run-Directory
           APT chdirs to this directory before invoking dpkg(1), the default
           is /.

       Build-options
           These options are passed to dpkg-buildpackage(1) when compiling
           packages; the default is to disable signing and produce all
           binaries.

       DPkg::ConfigurePending
           If this option is set APT will call dpkg --configure --pending to
           let dpkg(1) handle all required configurations and triggers. This
           option is activated by default, but deactivating it could be useful
           if you want to run APT multiple times in a row - e.g. in an
           installer. In this scenario you could deactivate this option in all
           but the last run.

PERIODIC AND ARCHIVES OPTIONS
       APT::Periodic and APT::Archives groups of options configure behavior of
       apt periodic updates, which is done by the
       /usr/lib/apt/apt.systemd.daily script. See the top of this script for
       the brief documentation of these options.

DEBUG OPTIONS
       Enabling options in the Debug:: section will cause debugging
       information to be sent to the standard error stream of the program
       utilizing the apt libraries, or enable special program modes that are
       primarily useful for debugging the behavior of apt. Most of these
       options are not interesting to a normal user, but a few may be:

       o   Debug::pkgProblemResolver enables output about the decisions made
           by dist-upgrade, upgrade, install, remove, purge.

       o   Debug::NoLocking disables all file locking. This can be used to run
           some operations (for instance, apt-get -s install) as a non-root
           user.

       o   Debug::pkgDPkgPM prints out the actual command line each time that
           apt invokes dpkg(1).

       o   Debug::IdentCdrom disables the inclusion of statfs data in CD-ROM
           IDs.

       A full list of debugging options to apt follows.

       Debug::Acquire::cdrom
           Print information related to accessing cdrom:// sources.

       Debug::Acquire::ftp
           Print information related to downloading packages using FTP.

       Debug::Acquire::http
           Print information related to downloading packages using HTTP.

       Debug::Acquire::https
           Print information related to downloading packages using HTTPS.

       Debug::Acquire::gpgv
           Print information related to verifying cryptographic signatures
           using gpg.

       Debug::aptcdrom
           Output information about the process of accessing collections of
           packages stored on CD-ROMs.

       Debug::BuildDeps
           Describes the process of resolving build-dependencies in apt-
           get(8).

       Debug::Hashes
           Output each cryptographic hash that is generated by the apt
           libraries.

       Debug::IdentCDROM
           Do not include information from statfs, namely the number of used
           and free blocks on the CD-ROM filesystem, when generating an ID for
           a CD-ROM.

       Debug::NoLocking
           Disable all file locking. For instance, this will allow two
           instances of "apt-get update" to run at the same time.

       Debug::pkgAcquire
           Log when items are added to or removed from the global download
           queue.

       Debug::pkgAcquire::Auth
           Output status messages and errors related to verifying checksums
           and cryptographic signatures of downloaded files.

       Debug::pkgAcquire::Diffs
           Output information about downloading and applying package index
           list diffs, and errors relating to package index list diffs.

       Debug::pkgAcquire::RRed
           Output information related to patching apt package lists when
           downloading index diffs instead of full indices.

       Debug::pkgAcquire::Worker
           Log all interactions with the sub-processes that actually perform
           downloads.

       Debug::pkgAutoRemove
           Log events related to the automatically-installed status of
           packages and to the removal of unused packages.

       Debug::pkgDepCache::AutoInstall
           Generate debug messages describing which packages are being
           automatically installed to resolve dependencies. This corresponds
           to the initial auto-install pass performed in, e.g., apt-get
           install, and not to the full apt dependency resolver; see
           Debug::pkgProblemResolver for that.

       Debug::pkgDepCache::Marker
           Generate debug messages describing which packages are marked as
           keep/install/remove while the ProblemResolver does his work. Each
           addition or deletion may trigger additional actions; they are shown
           indented two additional spaces under the original entry. The format
           for each line is MarkKeep, MarkDelete or MarkInstall followed by
           package-name <a.b.c -> d.e.f | x.y.z> (section) where a.b.c is the
           current version of the package, d.e.f is the version considered for
           installation and x.y.z is a newer version, but not considered for
           installation (because of a low pin score). The later two can be
           omitted if there is none or if it is the same as the installed
           version.  section is the name of the section the package appears
           in.

       Debug::pkgDPkgPM
           When invoking dpkg(1), output the precise command line with which
           it is being invoked, with arguments separated by a single space
           character.

       Debug::pkgDPkgProgressReporting
           Output all the data received from dpkg(1) on the status file
           descriptor and any errors encountered while parsing it.

       Debug::pkgOrderList
           Generate a trace of the algorithm that decides the order in which
           apt should pass packages to dpkg(1).

       Debug::pkgPackageManager
           Output status messages tracing the steps performed when invoking
           dpkg(1).

       Debug::pkgPolicy
           Output the priority of each package list on startup.

       Debug::pkgProblemResolver
           Trace the execution of the dependency resolver (this applies only
           to what happens when a complex dependency problem is encountered).

       Debug::pkgProblemResolver::ShowScores
           Display a list of all installed packages with their calculated
           score used by the pkgProblemResolver. The description of the
           package is the same as described in Debug::pkgDepCache::Marker

       Debug::sourceList
           Print information about the vendors read from
           /etc/apt/vendors.list.

       Debug::RunScripts
           Display the external commands that are called by apt hooks. This
           includes e.g. the config options DPkg::{Pre,Post}-Invoke or
           APT::Update::{Pre,Post}-Invoke.

EXAMPLES
       /usr/share/doc/apt/examples/configure-index.gz is a configuration file
       showing example values for all possible options.

FILES
       /etc/apt/apt.conf
           APT configuration file. Configuration Item: Dir::Etc::Main.

       /etc/apt/apt.conf.d/
           APT configuration file fragments. Configuration Item:
           Dir::Etc::Parts.

SEE ALSO
       apt-cache(8), apt-config(8), apt_preferences(5).

BUGS
       APT bug page[1]. If you wish to report a bug in APT, please see
       /usr/share/doc/debian/bug-reporting.txt or the reportbug(1) command.

AUTHORS
       Jason Gunthorpe

       APT team

       Daniel Burrows <dburrows@debian.org>
           Initial documentation of Debug::*.

NOTES
        1. APT bug page
           http://bugs.debian.org/src:apt

APT 1.8.1                      10 December 2018                    APT.CONF(5)

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