agetty

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:

       ·      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
              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 or directory
              instead of /etc/issue or /etc/issue.d.

       ·      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.

ARGUMENTS
       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
              "--".

       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
              switching.

              This argument is optional and unnecessary for virtual terminals.

              The default for serial terminals is keep the current baud rate
              (see --keep-baud) and if unsuccessful then default to '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.

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

       -a, --autologin username
              Automatically log in the specified user without asking for a
              username or password.  Using this option causes an -f username
              option and argument to be added to the /bin/login command line.
              See --login-options, which can be used to modify this option's
              behavior.

              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
              Do not reset terminal cflags (control modes).  See termios(3)
              for more details.

       -E, --remote
              Typically the login(1) command is given a remote hostname when
              called by something such as telnetd(8).  This option allows
              agetty to pass what it is using for a hostname to login(1) for
              use in utmp(5).  See --host, login(1), and utmp(5).

              If the --host fakehost option is given, then an -h fakehost
              option and argument are added to the /bin/login command line.

              If the --nohostname option is given, then an -H option is added
              to the /bin/login command line.

              See --login-options.

       -f, --issue-file file|directory
              Display the contents of file instead of /etc/issue.  If the
              specified path is a directory then displays all files with
              .issue file extension in version-sort order from the directory.
              This allows custom messages to be displayed on different
              terminals.  The --noissue 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 fakehost
              Write the specified fakehost 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 linefeed
              character (ASCII 10, octal 012), write \012.

       -J, --noclear
              Do not clear the screen before prompting for the login name.  By
              default the screen is 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.  Such a program
              could, for example, ask for a dial-up password or use a
              different password file. See --login-options.

       -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'.

              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.

              never  Explicitly clears the CLOCAL flag from the line setting
                     and the carrier-detect signal is expected on the line.

              auto   The 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 --extract-baud feature may fail on heavily-loaded
              systems, you still should enable BREAK processing by enumerating
              all expected baud rates on the command line.

       --list-speeds
              Display supported baud rates.  These are determined at
              compilation time.

       -n, --skip-login
              Do not prompt the user for a login name.  This can be used in
              connection with the --login-program option to invoke a non-
              standard login process such as a BBS system.  Note that with the
              --skip-login option, agetty gets no input from the user who logs
              in and therefore will not 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  and arguments that  are passed to login(1). Where \u is
              replaced by the login name. For example:

                  --login-options '-h darkstar -- \u'

              See --autologin, --login-program and --remote.

              Please read the SECURITY NOTICE below before using this option.

       -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.
              Use of this option with hardwired terminal lines is not
              recommended.

       -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 file (or
              others) and the login prompt.  This is useful with the
              --init-string 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
              gethostname(3P) or (if not found) by getaddrinfo(3) 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
              characters 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.

       --reload
              Ask all running agetty instances to reload and update their
              displayed prompts, if the user has not yet commenced logging in.
              After doing so the command will exit.  This feature might be
              unsupported on systems without Linux inotify(7).

       --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
       password: prompt):

              /sbin/agetty --local-line 9600 ttyS1 vt100

       For an old-style dial-in line with a 9600/2400/1200 baud modem:

              /sbin/agetty --extract-baud --timeout 60 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 --wait-cr --init-string 'ATE0Q1&D2&C1S0=1 15' 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
       depending on how the login binary parses the command line that might
       not be sufficient.  Check that the used login program cannot 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 FILES
       The default issue file is /etc/issue. If the file exists then agetty
       also checks for /etc/issue.d directory. The directory is optional
       extension to the default issue file and content of the directory is
       printed after /etc/issue content. If the /etc/issue does not exist than
       the directory is ignored. All files with .issue extension from the
       directory are printed in version-sort order. The directory allow to
       maintain 3rd-party messages independently on the primary system
       /etc/issue file.

       The default path maybe overridden by --issue-file option. In this case
       specified path has to be file or directory and the default /etc/issue
       as well as /etc/issue.d are ignored.

       The issue files 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 characters listed below.


       4 or 4{interface}
              Insert the IPv4 address of the specified network interface (for
              example: \4{eth0}).  If the interface argument is not specified,
              then select the first fully configured (UP, non-LOCALBACK,
              RUNNING) interface.  If not any configured interface is found,
              fall back to the IP address of the machine's 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.

       e or e{name}
              Translate the human-readable name to an escape sequence and
              insert it (for example: \e{red}Alert text.\e{reset}).  If the
              name argument is not specified, then insert \033.  The currently
              supported names are: black, blink, blue, bold, brown, cyan,
              darkgray, gray, green, halfbright, lightblue, lightcyan,
              lightgray, lightgreen, lightmagenta, lightred, magenta, red,
              reset, reverse, and yellow.  All unknown names are silently
              ignored.

       s      Insert the system name (the name of the operating system).  Same
              as 'uname -s'.  See also the \S escape code.

       S or S{VARIABLE}
              Insert the VARIABLE data from /etc/os-release.  If this file
              does not exist then fall back to /usr/lib/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, that is, the build-date and such.

       An 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 /usr/lib/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 --extract-baud 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 --extract-baud 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 --extract-baud 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
       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.

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 https://www.kernel.org/pub/linux/utils/util-linux/.



util-linux                       February 2016                       AGETTY(8)