agetty(glossar.html) - phpMan

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 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:  Control-U (kill); DEL and
              back space (erase); carriage return and line feed (end of line).
              See also --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 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.
              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  virtual  termi-
              nal, or 'hurd' for GNU Hurd on 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 behaviour and then only \u is replaced by
              the username and no other option is added to the  login  command
              line.
              Note  that --autologin may affect the way how agetty initializes
              the serial line, because on auto-login agetty does not read from
              the line and it has no opportunity optimize the line setting.
       -c, --noreset
              Don't  reset terminal cflags (control modes). See termios(3) for
              more details.
       -E, --remote
              If -H fakehost option is given then -r fakehost options 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.
       -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: "<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
              shells.
       -r, --chroot "directory"
              Change root to the specified directory.
       -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).
       --nohints
              Do not print hints about Num, Caps and Scroll Locks.
       --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 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.
       --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 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.

       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
              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 AT suse.de>
       Karel Zak <kzak AT redhat.com>
       The  original  agetty  for  serial terminals was written by W.Z. Venema
       <wietse AT wzv.nl>  and  ported   to   Linux   by   Peter   Orbaek
       <poe AT daimi.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)