getty(8)



AGETTY(8)                    System Administration                   AGETTY(8)

NAME
       agetty - alternative Linux getty

SYNOPSIS
       agetty [options] port [baud_rate...]  [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  hardwired
       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
              backspace (erase); carriage return and line feed (end of  line).
              See also the --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
              /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 hardware 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.

              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.

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

       -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  behavior and then only \u is replaced by
              the username and no other option is added to the  login  command
              line.

       -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
              appropriate.

       -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.

       -J,--noclear
              Do not clear the screen before prompting for the login name (the
              screen is normally 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 (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.

       -N, --nonewline
              Do not print a newline before writing out /etc/issue.

       -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
              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 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
              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 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.

       --chdir directory
              Change directory before the login.

       --delay number
              Sleep seconds before open tty.

       --nice number
              Run login with this priority.

       --version
              Display version information and exit.

       --help Display help text and exit.

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 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

SECURITY NOTICE
       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
       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
       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 the specified network interface (e.g.
              \4{eth0}) and if the interface argument is  not  specified  then
              select  the  first fully configured (UP, non-LOCALBACK, RUNNING)
              interface. If not found any configured interface fall back to IP
              address of the machine 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.

       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
              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 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.

       /etc/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
       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.

AUTHORS
       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
       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)

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