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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  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 pro‐
	      duced 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

       ·      Optionally does not ask for a login name.

       ·      Optionally invokes  a  non-standard  login  program  instead  of

       ·      Optionally turns on hardware flow control

       ·      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 a virtual termi‐
	      nal, or 'hurd' for GNU Hurd on a 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

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

       -E, --remote
	      If an -H fakehost option is given, then an -r fakehost option 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[=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'.

	      The mode '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.

	      The mode 'never' explicitly clears the CLOCAL flag from the line
	      setting and the carrier-detect signal is expected on the line.

	      The mode 'auto' (agetty default) does not modify the CLOCAL set‐
	      ting 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  -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 the -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 the 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
	      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 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 hardwired 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 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 -L 9600 ttyS1 vt100

       For an 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 turns 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, time
       etcetera.  All escape codes consist of a backslash (\) immediately fol‐
       lowed 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 (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 ⟨⟩
       Karel Zak ⟨⟩

       The original agetty for serial terminals was  written  by  W.Z.	Venema
       <>	 and   ported	to   Linux   by	 Peter	Orbaek

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

util-linux			   May 2011			     AGETTY(8)

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