getty(8)



AGETTY(8)                    System Administration                   AGETTY(8)

NAME
       agetty - alternative Linux getty

SYNOPSIS
       agetty [options] port [baud_rate...] [term]

DESCRIPTION
       agetty  opens  a  tty  port,  prompts  for a login name and invokes the
       /bin/login command.  It is normally invoked by init(8).

       agetty has several non-standard features that are useful for  hardwired
       and for dial-in lines:

       o      Adapts  the tty settings to parity bits and to erase, kill, end-
              of-line and uppercase characters when it  reads  a  login  name.
              The  program can handle 7-bit characters with even, odd, none or
              space parity, and 8-bit characters with no parity.  The  follow-
              ing special characters are recognized: Control-U (kill); DEL and
              backspace (erase); carriage return and line feed (end of  line).
              See also the --erase-chars and --kill-chars options.

       o      Optionally  deduces the baud rate from the CONNECT messages pro-
              duced by Hayes(tm)-compatible modems.

       o      Optionally does not hang up when it is given an  already  opened
              line (useful for call-back applications).

       o      Optionally does not display the contents of the /etc/issue file.

       o      Optionally   displays  an  alternative  issue  file  instead  of
              /etc/issue.

       o      Optionally does not ask for a login name.

       o      Optionally invokes  a  non-standard  login  program  instead  of
              /bin/login.

       o      Optionally turns on hardware flow control.

       o      Optionally  forces the line to be local with no need for carrier
              detect.

       This program does not use the /etc/gettydefs (System  V)  or  /etc/get-
       tytab (SunOS 4) files.

ARGUMENTS
       port   A  path name relative to the /dev directory.  If a "-" is speci-
              fied, agetty assumes that its standard  input  is  already  con-
              nected  to a tty port and that a connection to a remote user has
              already been established.

              Under System V, a "-" port argument  should  be  preceded  by  a
              "--".

       baud_rate,...
              A  comma-separated  list  of  one or more baud rates.  Each time
              agetty receives a BREAK character it advances through the  list,
              which is treated as if it were circular.

              Baud  rates should be specified in descending order, so that the
              null character (Ctrl-@) can also be used for  baud-rate  switch-
              ing.

              This argument is optional and unnecessary for virtual terminals.

              The  default  for serial terminals is keep the current baud rate
              (see --keep-baud) and if unsuccessful then default to '9600'.

       term   The value to be used for the TERM  environment  variable.   This
              overrides  whatever  init(8)  may  have set, and is inherited by
              login and the shell.

              The default is 'vt100', or 'linux' for Linux on a virtual termi-
              nal, or 'hurd' for GNU Hurd on a virtual terminal.

OPTIONS
       -8, --8bits
              Assume  that the tty is 8-bit clean, hence disable parity detec-
              tion.

       -a, --autologin username
              Automatically log in the specified user  without  asking  for  a
              username  or  password.  Using this option causes an -f username
              option and argument to be added to the /bin/login command  line.
              See  --login-options,  which can be used to modify this option's
              behavior.

       -c, --noreset
              Do not reset terminal cflags (control  modes).   See  termios(3)
              for more details.

       -E, --remote
              Typically  the  login(1) command is given a remote hostname when
              called by something such  as  telnetd(8).   This  option  allows
              agetty  to  pass what it is using for a hostname to login(1) for
              use in utmp(5).  See --host, login(1), and utmp(5).

              If the --host fakehost option is  given,  then  an  -h  fakehost
              option and argument are added to the /bin/login command line.

              If  the --nohostname option is given, then an -H option is added
              to the /bin/login command line.

              See --login-options.

       -f, --issue-file issue_file
              Display the contents of issue_file instead of /etc/issue.   This
              allows  custom  messages to be displayed on different terminals.
              The --noissue option will override this option.

       -h, --flow-control
              Enable hardware (RTS/CTS) flow control.  It is left  up  to  the
              application  to  disable software (XON/XOFF) flow protocol where
              appropriate.

       -H, --host fakehost
              Write the specified fakehost into the utmp file.   Normally,  no
              login  host  is  given, since agetty is used for local hardwired
              connections and consoles.  However, this option  can  be  useful
              for identifying terminal concentrators and the like.

       -i, --noissue
              Do  not  display  the  contents  of /etc/issue (or other) before
              writing the login prompt.  Terminals or communications  hardware
              may  become  confused  when  receiving lots of text at the wrong
              baud rate; dial-up scripts may fail if the login prompt is  pre-
              ceded by too much text.

       -I, --init-string initstring
              Set  an  initial  string  to  be sent to the tty or modem before
              sending anything else.  This may be used to initialize a  modem.
              Non-printable characters may be sent by writing their octal code
              preceded by a backslash (\).  For example, to  send  a  linefeed
              character (ASCII 10, octal 012), write \012.

       -J, --noclear
              Do not clear the screen before prompting for the login name.  By
              default the screen is cleared.

       -l, --login-program login_program
              Invoke the specified login_program instead of /bin/login.   This
              allows  the use of a non-standard login program.  Such a program
              could, for example, ask for a dial-up password or use a  differ-
              ent password file. See --login-options.

       -L, --local-line[=mode]
              Control  the  CLOCAL  line  flag.  The optional mode argument is
              'auto', 'always' or 'never'.  If the mode argument  is  omitted,
              then the default is 'always'.  If the --local-line option is not
              given at all, then the default is 'auto'.

              always Forces the line to be a local line with no need for  car-
                     rier  detect.  This can be useful when you have a locally
                     attached terminal where the serial line does not set  the
                     carrier-detect signal.

              never  Explicitly  clears  the CLOCAL flag from the line setting
                     and the carrier-detect signal is expected on the line.

              auto   The agetty default.  Does not modify the  CLOCAL  setting
                     and follows the setting enabled by the kernel.

       -m, --extract-baud
              Try  to  extract  the  baud rate from the CONNECT status message
              produced by Hayes(tm)-compatible modems.  These status  messages
              are of the form: "<junk><speed><junk>".  agetty assumes that the
              modem emits its status message at the same  speed  as  specified
              with (the first) baud_rate value on the command line.

              Since the --extract-baud feature may fail on heavily-loaded sys-
              tems, you still should enable BREAK  processing  by  enumerating
              all expected baud rates on the command line.

       -n, --skip-login
              Do  not  prompt  the user for a login name.  This can be used in
              connection with the --login-program option to invoke a non-stan-
              dard  login  process  such  as a BBS system.  Note that with the
              --skip-login option, agetty gets no input from the user who logs
              in  and therefore will not be able to figure out parity, charac-
              ter size, and newline processing of the connection.  It defaults
              to space parity, 7 bit characters, and ASCII CR (13) end-of-line
              character.  Beware that the program that agetty starts  (usually
              /bin/login) is run as root.

       -N, --nonewline
              Do not print a newline before writing out /etc/issue.

       -o, --login-options "login_options"
              Options  and arguments that  are passed to login(1). Where \u is
              replaced by the login name. For example:

                  --login-options '-h darkstar -- \u'

              See --autologin, --login-program and --remote.

              Please read the SECURITY NOTICE below before using this option.

       -p, --login-pause
              Wait for any key before dropping to the login  prompt.   Can  be
              combined  with  --autologin  to  save  memory by lazily spawning
              shells.

       -r, --chroot directory
              Change root to the specified directory.

       -R, --hangup
              Call vhangup() to do a virtual hangup of the specified terminal.

       -s, --keep-baud
              Try to keep the existing baud rate.  The  baud  rates  from  the
              command line are used when agetty receives a BREAK character.

       -t, --timeout timeout
              Terminate  if no user name could be read within timeout seconds.
              Use of this option with hardwired terminal lines is  not  recom-
              mended.

       -U, --detect-case
              Turn  on support for detecting an uppercase-only terminal.  This
              setting will detect a login name  containing  only  capitals  as
              indicating an uppercase-only terminal and turn on some upper-to-
              lower case conversions.  Note that this has no support  for  any
              Unicode characters.

       -w, --wait-cr
              Wait  for  the  user or the modem to send a carriage-return or a
              linefeed character before sending the /etc/issue file  (or  oth-
              ers)   and   the   login   prompt.   This  is  useful  with  the
              --init-string option.

       --nohints
              Do not print hints about Num, Caps and Scroll Locks.

       --nohostname
              By default the hostname  will  be  printed.   With  this  option
              enabled, no hostname at all will be shown.

       --long-hostname
              By  default  the  hostname  is only printed until the first dot.
              With this option enabled, the fully qualified hostname by  geth-
              ostname(3P) or (if not found) by getaddrinfo(3) is shown.

       --erase-chars string
              This  option  specifies  additional  characters  that  should be
              interpreted as a backspace  ("ignore  the  previous  character")
              when  the  user  types  the  login name.  The default additional
              'erase' has been '#', but since util-linux  2.23  no  additional
              erase characters are enabled by default.

       --kill-chars string
              This  option  specifies  additional  characters  that  should be
              interpreted as a kill ("ignore all  previous  characters")  when
              the  user  types  the login name.  The default additional 'kill'
              has been '@', but since util-linux 2.23 no additional kill char-
              acters are enabled by default.

       --chdir directory
              Change directory before the login.

       --delay number
              Sleep seconds before open tty.

       --nice number
              Run login with this priority.

       --reload
              Ask all running agetty instances to reload and update their dis-
              played prompts, if the user has not yet  commenced  logging  in.
              After  doing  so  the  command will exit.  This feature might be
              unsupported on systems without Linux inotify(7).

       --version
              Display version information and exit.

       --help Display help text and exit.

EXAMPLES
       This section shows examples for the process field of an  entry  in  the
       /etc/inittab  file.   You'll have to prepend appropriate values for the
       other fields.  See inittab(5) for more details.

       For a hardwired line or a console tty:

              /sbin/agetty 9600 ttyS1

       For a directly connected terminal without proper carrier-detect  wiring
       (try  this  if  your terminal just sleeps instead of giving you a pass-
       word: prompt):

              /sbin/agetty --local-line 9600 ttyS1 vt100

       For an old-style dial-in line with a 9600/2400/1200 baud modem:

              /sbin/agetty --extract-baud --timeout 60 ttyS1 9600,2400,1200

       For a Hayes modem with a fixed 115200 bps interface to the machine (the
       example  init  string  turns  off  modem  echo  and result codes, makes
       modem/computer DCD track modem/modem DCD, makes a DTR drop cause a dis-
       connection, and turns on auto-answer after 1 ring):

              /sbin/agetty --wait-cr --init-string 'ATE0Q1&D2&C1S0=1 15' 115200 ttyS1

SECURITY NOTICE
       If you use the --login-program and --login-options  options,  be  aware
       that  a malicious user may try to enter lognames with embedded options,
       which then get passed to the used login program.  Agetty does check for
       a  leading  "-" and makes sure the logname gets passed as one parameter
       (so embedded spaces will not create yet another parameter), but depend-
       ing  on  how the login binary parses the command line that might not be
       sufficient.  Check that the used login program cannot  be  abused  this
       way.

       Some   programs  use  "--" to indicate that the rest of the commandline
       should not be interpreted as options.  Use this feature if available by
       passing "--" before the username gets passed by \u.

ISSUE ESCAPES
       The  issue-file  (/etc/issue,  or  the  file  set with the --issue-file
       option) may contain certain escape codes to display  the  system  name,
       date, time etcetera.  All escape codes consist of a backslash (\) imme-
       diately followed by one of the characters listed below.

       4 or 4{interface}
              Insert the IPv4 address of the specified network interface  (for
              example: \4{eth0}).  If the interface argument is not specified,
              then select the first fully configured (UP, non-LOCALBACK,  RUN-
              NING) interface.  If not any configured interface is found, fall
              back to the IP address of the machine's hostname.

       6 or 6{interface}
              The same as \4 but for IPv6.

       b      Insert the baudrate of the current line.

       d      Insert the current date.

       e or e{name}
              Translate the human-readable name  to  an  escape  sequence  and
              insert  it  (for  example: \e{red}Alert text.\e{reset}).  If the
              name argument is not specified, then insert \033.  The currently
              supported  names  are:  black,  blink,  blue, bold, brown, cyan,
              darkgray,  gray,  green,   halfbright,   lightblue,   lightcyan,
              lightgray,  lightgreen,  lightmagenta,  lightred,  magenta, red,
              reset, reverse, and yellow.   All  unknown  names  are  silently
              ignored.

       s      Insert the system name (the name of the operating system).  Same
              as 'uname -s'.  See also the \S escape code.

       S or S{VARIABLE}
              Insert the VARIABLE data from  /etc/os-release.   If  this  file
              does  not  exist  then fall back to /usr/lib/os-release.  If the
              VARIABLE argument is not specified, then  use  PRETTY_NAME  from
              the  file  or the system name (see \s).  This escape code allows
              to keep /etc/issue distribution and release  independent.   Note
              that  \S{ANSI_COLOR}  is  converted  to the real terminal escape
              sequence.

       l      Insert the name of the current tty line.

       m      Insert the architecture identifier  of  the  machine.   Same  as
              'uname -m'.

       n      Insert  the nodename of the machine, also known as the hostname.
              Same as 'uname -n'.

       o      Insert the NIS domainname of the  machine.   Same  as  'hostname
              -d'.

       O      Insert the DNS domainname of the machine.

       r      Insert the release number of the OS.  Same as 'uname -r'.

       t      Insert the current time.

       u      Insert the number of current users logged in.

       U      Insert  the string "1 user" or "<n> users" where <n> is the num-
              ber of current users logged in.

       v      Insert the version of the OS, that is, the build-date and such.

       An example.  On my system, the following /etc/issue file:

              This is \n.\o (\s \m \r) \t

       displays as:

              This is thingol.orcan.dk (Linux i386 1.1.9) 18:29:30

FILES
       /var/run/utmp
              the system status file.

       /etc/issue
              printed before the login prompt.

       /etc/os-release /usr/lib/os-release
              operating system identification data.

       /dev/console
              problem reports (if syslog(3) is not used).

       /etc/inittab
              init(8) configuration file for SysV-style init daemon.

BUGS
       The baud-rate detection feature (the  --extract-baud  option)  requires
       that agetty be scheduled soon enough after completion of a dial-in call
       (within 30 ms with modems that talk at  2400  baud).   For  robustness,
       always  use  the  --extract-baud  option in combination with a multiple
       baud rate command-line argument, so that BREAK processing is enabled.

       The text in the /etc/issue file (or other) and  the  login  prompt  are
       always output with 7-bit characters and space parity.

       The  baud-rate  detection  feature (the --extract-baud option) requires
       that the modem emits its status message after raising the DCD line.

DIAGNOSTICS
       Depending on how the program was configured, all diagnostics are  writ-
       ten  to  the  console  device  or  reported via the syslog(3) facility.
       Error messages are produced if the port argument  does  not  specify  a
       terminal  device;  if  there  is  no utmp entry for the current process
       (System V only); and so on.

AUTHORS
       Werner Fink <werner@suse.de>
       Karel Zak <kzak@redhat.com>

       The original agetty for serial terminals was  written  by  W.Z.  Venema
       <wietse@wzv.win.tue.nl>   and   ported   to   Linux   by  Peter  Orbaek
       <poe@daimi.aau.dk>.

AVAILABILITY
       The agetty command is part of the util-linux package and  is  available
       from https://www.kernel.org/pub/linux/utils/util-linux/.

util-linux                       February 2016                       AGETTY(8)

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