NAME | SYNOPSIS | DESCRIPTION | ARGUMENTS | OPTIONS | EXAMPLES | SECURITY NOTICE | ISSUE ESCAPES | FILES | BUGS | DIAGNOSTICS | AUTHORS | AVAILABILITY | COLOPHON

AGETTY(8)                   System Administration                  AGETTY(8)

NAME         top

       agetty - alternative Linux getty

SYNOPSIS         top

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

DESCRIPTION         top

       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:

       ·      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  following  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.

       ·      Optionally deduces the baud rate  from  the  CONNECT  messages
              produced by Hayes(tm)-compatible modems.

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

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

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

       ·      Optionally does not ask for a login name.

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

       ·      Optionally turns on hardware flow control.

       ·      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/gettytab (SunOS 4) files.

ARGUMENTS         top

       port   A  path  name  relative  to  the  /dev directory.  If a "-" is
              specified, agetty assumes that its standard input  is  already
              connected 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
              switching.

              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
              terminal, or 'hurd' for GNU Hurd on a virtual terminal.

OPTIONS         top

       -8, --8bits
              Assume that the tty  is  8-bit  clean,  hence  disable  parity
              detection.

       -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 preceded 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 different 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
                     carrier 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
              systems,  you  still  should  enable   BREAK   processing   by
              enumerating all expected baud rates on the command line.

       --list-speeds
              Display   supported  baud  rates.   These  are  determined  at
              compilation time.

       -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-
              standard 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,   character   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 recommended.

       -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
              others)  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
              gethostname(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
              characters 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
              displayed 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         top

       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
       password: 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
       disconnection, and turns on auto-answer after 1 ring):

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

SECURITY NOTICE         top

       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 depending 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         top

       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 (\)
       immediately 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, RUNNING) 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
              number 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         top

       /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         top

       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         top

       Depending  on  how  the  program  was configured, all diagnostics are
       written 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         top

       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         top

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

COLOPHON         top

       This page is part of the util-linux (a random collection of Linux
       utilities) project.  Information about the project can be found at 
       ⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩.  If you have a
       bug report for this manual page, send it to
       util-linux@vger.kernel.org.  This page was obtained from the
       project's upstream Git repository 
       ⟨git://git.kernel.org/pub/scm/utils/util-linux/util-linux.git⟩ on
       2017-09-15.  If you discover any rendering problems in this HTML ver‐
       sion of the page, or you believe there is a better or more up-to-date
       source for the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original man‐
       ual page), send a mail to man-pages@man7.org

util-linux                      February 2016                      AGETTY(8)

Pages that refer to this page: tty(4)ttyS(4)issue(5)systemd.exec(5)ttytype(5)utmp(5)systemd-getty-generator(8)