focal (8) agetty.8.gz

Provided by: util-linux_2.34-0.1ubuntu9.6_amd64 bug

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/.