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AGETTY(8)                    System Administration                   AGETTY(8)



NAME
       agetty - alternative Linux getty


SYNOPSIS
       agetty  [-8chiLmnsUw]  [-a  user]  [-f  issue_file] [-H login_host] [-I
       init] [-l login_program] [-t timeout] 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 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, --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 behaviour 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.

       -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.

       -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-
              nal.

       -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: "".   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 -- ".

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

       -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
              option.

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

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

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

       --version
              Output version information and exit.

       --help Output help screen 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 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


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  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 " users" where  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 
       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.


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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