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 files or directories 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(1) 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 in which getty 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 path
           Specifies a ":" delimited list of files and directories to be
           displayed instead of /etc/issue (or other). All specified files and
           directories are displayed, missing or empty files are silently
           ignored. If the specified path is a directory then display 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.

       --show-issue
           Display the current issue file (or other) on the current terminal and
           exit. Use this option to review the current setting, it is not
           designed for any other purpose. Note that output may use some default
           or incomplete information as proper output depends on terminal and
           agetty command line.

       -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 \12.

       -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(2) 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. If another baud
           rates specified then the original baud rate is also saved to the end
           of the wanted baud rates list. This can be used to return to the
           original baud rate after unexpected BREAKs.

       -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.

EXAMPLE
       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\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 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 command line
       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, then
       the directory is ignored. All files with .issue extension from the
       directory are printed in version-sort order. The directory can be used to
       maintain 3rd-party messages independently on the primary system
       /etc/issue file.

       Since version 2.35 additional locations for issue file and directory are
       supported. If the default /etc/issue does not exist, then agetty checks
       for /run/issue and /run/issue.d, thereafter for /usr/lib/issue and
       /usr/lib/issue.d. The directory /etc is expected for host specific
       configuration, /run is expected for generated stuff and /usr/lib for
       static distribution maintained configuration.

       The default path maybe overridden by --issue-file option. In this case
       specified path has to be file or directory and all the default issue file
       and directory locations are ignored.

       The issue file feature can be completely disabled by --noissue option.

       It is possible to review the current issue file by agetty --show-issue on
       the current terminal.

       The issue files may contain certain escape codes to display the system
       name, date, time et cetera. 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, yellow and
           white. 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 can be used 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>.

REPORTING BUGS
       For bug reports, use the issue tracker at
       https://github.com/karelzak/util-linux/issues.

AVAILABILITY
       The agetty command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>.



util-linux 2.37.2                  2021-06-02                          AGETTY(8)