agetty man page on aLinux

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AGETTY(8)							     AGETTY(8)

NAME
       agetty - alternative Linux getty

SYNOPSIS
       agetty  [-8ihLmnUw]  [-f	 issue_file]  [-l login_program] [-I init] [-t
       timeout] [-H login_host] port baud_rate,...  [term]
       agetty [-8ihLmnw] [-f issue_file]  [-l  login_program]  [-I  init]  [-t
       timeout] [-H login_host] baud_rate,...  port [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 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: @ and Control-U (kill); #,
	      DEL and back space (erase); carriage return and line  feed  (end
	      of line).

       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 hard-ware 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.

       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.

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

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

       -i     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.

       -f 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.

       -I 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
	      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).

       -H 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.

       -m     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     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.

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

       -L     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‐
	      nal.

       -U     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  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
	      option.

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 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

ISSUE ESCAPES
       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.

       b      Insert the baudrate of the current line.

       d      Insert the current date.

       s      Insert the system name, the name of the operating system.

       l      Insert the name of the current tty line.

       m      Insert the architecture identifier of the machine, eg. i486

       n      Insert the nodename of the machine, also known as the hostname.

       o      Insert the NIS domainname of the machine.

       O      Insert the DNS domainname of the machine.

       r      Insert the release number of the OS, eg. 1.1.9.

       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

FILES
       /var/run/utmp, the system status file.
       /etc/issue, printed before the login prompt.
       /dev/console, problem reports (if syslog(3) is not used).
       /etc/inittab, init(8) configuration file.

BUGS
       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.

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.

AUTHOR(S)
       W.Z. Venema <wietse@wzv.win.tue.nl>
       Eindhoven University of Technology
       Department of Mathematics and Computer Science
       Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

       Peter Orbaek <poe@daimi.aau.dk>
       Linux port and more options. Still maintains the code.

       Eric Rasmussen <ear@usfirst.org>
       Added -f option to display custom login messages on different terminals.

AVAILABILITY
       The agetty command is part of the util-linux-ng package and is avail‐
       able from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.

								     AGETTY(8)
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