agetty manpage

Search topic Section

AGETTY(8)		     System Administration		     AGETTY(8)

       agetty - alternative Linux getty

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

       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 hard-wired
       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 following
	      special  characters  are	recognized:  Control-U (kill); DEL and
	      back space (erase); carriage return and line feed (end of line).
	      See also --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

       o      Optionally does not ask for a login name.

       o      Optionally invokes  a  non-standard  login  program  instead  of

       o      Optionally turns on hard-ware flow control

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

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

       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

	      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-

	      This argument is optional and unnecessary for virtual terminals.
	      The default for serial terminals is '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  virtual	termi-
	      nal, or 'hurd' for GNU Hurd on virtual terminal.

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

       -a, --autologin username
	      Log the specified user automatically in  without	asking	for  a
	      login  name and password. The -f username option is added to the
	      /bin/login command line by default. The  --login-options	option
	      changes  this  default behaviour and then only \u is replaced by
	      the username and no other option is added to the	login  command

	      Note  that --autologin may affect the way how agetty initializes
	      the serial line, because on auto-login agetty does not read from
	      the line and it has no opportunity optimize the line setting.

       -c, --noreset
	      Don't  reset terminal cflags (control modes). See termios(3) for
	      more details.

       -E, --remote
	      If -H fakehost option is given then -r fakehost options is added
	      to the /bin/login command line.

       -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 -i 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

       -H, --host login_host
	      Write the specified login_host 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.

       -l, --login-program login_program
	      Invoke the specified login_program instead of /bin/login.	  This
	      allows the use of a non-standard login program (for example, one
	      that asks for a dial-up password or that uses a different	 pass-
	      word file).

       -L, --local-line
	      Force  the  line	to  be	a  local line with no need for carrier
	      detect. This can be useful when you have a locally attached ter-
	      minal where the serial line does not set the carrier detect sig-

       -m, --extract-baud
	      Try to extract the baud rate 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 -m feature may fail  on	 heavily-loaded	 systems,  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 -l option to invoke a non-standard login process
	      such as a BBS system. Note that with the -n option, agetty  gets
	      no  input	 from  user who logs in and therefore won't 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.

       -o, --login-options "login_options"
	      Options	that  are passed to the login program.	\u is replaced
	      by the login  name.  The	default	 /bin/login  command  line  is
	      "/bin/login -- <username>".

	      Please read the SECURITY NOTICE below if you want to use this.

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

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

       -R, --hangup
	      Do call vhangup() for a virtually hangup of the specified termi-

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

       -t, --timeout timeout
	      Terminate	 if no user name could be read within timeout seconds.
	      This option should probably not be used with hard-wired lines.

       -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 (or other) file
	      and the login prompt. Very useful	 in  connection	 with  the  -I

	      Do not clear the screen before prompting for the login name (the
	      screen is normally cleared).

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

	      Do not print a newline before writing out /etc/issue.

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

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

	      Display version information and exit.

       --help Display help text and exit.

       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 hard-wired line or a console tty:

	      /sbin/agetty 9600 ttyS1

       For  a  directly	 connected  terminal  without  proper  carriage detect
       wiring: (try this if your terminal just sleeps instead of giving you  a
       password: prompt.)

	      /sbin/agetty -L 9600 ttyS1 vt100

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

	      /sbin/agetty -mt60 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 turn on auto-answer after 1 ring.)

	      /sbin/agetty -w -I 'ATE0Q1&D2&C1S0=1\015' 115200 ttyS1

       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 can not be  abused  this

       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.

       The issue-file (/etc/issue or the file set with the -f option) may con-
       tain certain escape codes to display the system	name,  date  and  time
       etc.  All  escape codes consist of a backslash (\) immediately followed
       by one of the letters explained below.

       4 or 4{interface}
	      Insert the IPv4 address of the machine hostname or IPv4  address
	      the  configured  network	interface if the interface argument is
	      specified (e.g. \4{eth0}).

       6 or 6{interface}
	      Insert the IPv6 address of the machine hostname or IPv6  address
	      the  configured  network	interface if the interface argument is
	      specified (e.g. \6{eth0}}

       b      Insert the baudrate of the current line.

       d      Insert the current date.

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

       S or S{VARIABLE}
	      Insert  the VARIABLE data from /etc/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

       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, eg. the build-date etc.

       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

	      the system status file.

	      printed before the login prompt.

	      operating system identification data.

	      problem reports (if syslog(3) is not used).

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

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

       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.

       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

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

util-linux			   May 2011			     AGETTY(8)