agetty man page on ElementaryOS

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AGETTY(8)		     System Administration		     AGETTY(8)

       agetty - alternative Linux getty

       agetty  [-8chiLmnsUw]  [-a  user]  [-f  issue_file] [-H login_host] [-I
       init] [-l login_program] [-t timeout] 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: @ 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

       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‐

       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.

       -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

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

       -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, --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 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 full qualified hostname  by	 geth‐
	      ostname() or if not found by gethostbyname() is shown.

	      Output version information and exit.

       --help Output help screen 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.

       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'.

       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 (Linux i386 1.1.9) 18:29:30

       /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.

       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.

       W.Z. Venema <>
       Eindhoven University of Technology
       Department of Mathematics and Computer Science
       Den Dolech 2, P.O. Box 513, 5600 MB Eindhoven, The Netherlands

       Peter Orbaek <>
       Linux port and more options. Still maintains the code.

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

       The agetty command is part of the util-linux package and is available

util-linux			   May 2011			     AGETTY(8)

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