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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

       ·      Adapts  the  tty settings to parity bits and to erase, kill, end-of-line and upper‐
              case characters when it reads a login name.  The program can handle  7-bit  charac‐
              ters 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   produced   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 /etc/issue.

       ·      Optionally does not ask for a login name.

       ·      Optionally invokes a non-standard login program instead of /bin/login.

       ·      Optionally turns on hardware flow control

       ·      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/gettytab (SunOS 4) files.

       port   A path name relative to the /dev directory. If a "-" is specified,  agetty  assumes
              that its standard input is already connected 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 switching.

              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 terminal, or  'hurd'  for
              GNU Hurd on a virtual terminal.

       -8, --8bits
              Assume that the tty is 8-bit clean, hence disable parity detection.

       -a, --autologin username
              Log  the  specified user automatically in without asking for a login name and pass‐
              word. 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 mes‐
              sages to be displayed on different terminals.  The -i  option  will  override  this

       -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 preceded 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 line‐
              feed character (ASCII 10, octal 012), write \012.

              Do not clear the screen before prompting for the login name (the screen is normally

       -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 password 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 setting 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 connec‐
              tion.  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 command 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.

              Do not print hints about Num, Caps and Scroll Locks.

              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 gethostname() or (if not found) by  getad‐
              drinfo() 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 addi‐
              tional 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.

              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

       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 password: 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 disconnection, 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 depending 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 inter‐
       preted 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 contain certain escape
       codes to display the system name, date, time etcetera.  All  escape  codes  consist  of  a
       backslash (\) immediately followed 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 number 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

              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 written  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 ⟨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>.

       The agetty command is part of the util-linux package and is available from  ftp://ftp.ker‐

util-linux                                   May 2011                                   AGETTY(8)

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