inittab(4)                                                       inittab(4)

NAME
     inittab - script for the boot init process

DESCRIPTION

     The /etc/inittab file supplies the script to the boot init daemon in
     its role as a general process dispatcher (see init(1M)).  The process
     that constitutes the majority of boot init's process dispatching
     activities is the line process /usr/sbin/getty that initiates
     individual terminal lines.  Other processes typically dispatched by
     boot init are daemons and shells.

     The inittab file is composed of entries that are position-dependent
     and have the following format:

          id:rstate:action:process

     Each entry is delimited by a newline; however, a backslash ()
     preceding a newline indicates a continuation of the entry.  Up to 1024
     characters per entry are permitted.  Comments can be inserted in the
     process field by starting a "word" with a # (see sh(1)).  Comments for
     lines that spawn gettys are displayed by the who command (see who(1)).
     It is expected that they will contain some information about the line
     such as the location.  There are no limits (other than maximum entry
     size) imposed on the number of entries within the inittab file.

     The entry fields are:

          id        A one- to four-character value used to uniquely
                    identify an entry.  Duplicate entries cause an error
                    message to be issued, but are otherwise ignored.  The
                    use of a four-character value to identify an entry is
                    strongly recommended (see WARNINGS below).

          rstate    Defines the run level in which this entry is to be
                    processed.  Run levels correspond to a configuration of
                    processes in the system where each process spawned by
                    boot init is assigned one or more run levels in which
                    it is allowed to exist.  Run levels are represented by
                    a number in the range 0 through 6.  For example, if the
                    system is in run level 1, only those entries having a 1
                    in their rstate field are processed.

                    When boot init is requested to change run levels, all
                    processes that do not have an entry in the rstate field
                    for the target run level are sent the warning signal
                    (SIGTERM) and allowed a 20-second grace period before
                    being forcibly terminated by a kill signal (SIGKILL).
                    You can specify multiple run levels for a process by
                    entering more than one run level value in any
                    combination.  If no run level is specified, the process
                    is assumed to be valid for all run levels, 0 through 6.

                    Three other values, a, b and c, can also appear in the
                    rstate field, even though they are not true run levels.
                    Entries having these characters in the rstate field are
                    processed only when a user init process requests them
                    to be run (regardless of the current system run level).
                    They differ from run levels in that boot init can never
                    enter "run level" a, b, or c.  Also, a request for the
                    execution of any of these processes does not change the
                    current numeric run level.

                    Furthermore, a process started by an a, b, or c option
                    is not killed when boot init changes levels.  A process
                    is killed only if its line in inittab is marked off in
                    the action field, its line is deleted entirely from
                    inittab, or boot init goes into the single-user state.

          action    A keyword in this field tells boot init how to treat
                    the process specified in the process field.  The
                    following actions can be specified:

                    boot              Process the entry only at boot init's
                                      boot-time read of the inittab file.
                                      Boot init starts the process, does
                                      not wait for its termination, and
                                      when it dies, does not restart the
                                      process.  In order for this
                                      instruction to be meaningful, the
                                      rstate should be the default or it
                                      must match boot init's run level at
                                      boot time.  This action is useful for
                                      an initialization function following
                                      a hardware boot of the system.

                    bootwait          Process the entry only at boot init's
                                      boot-time read of the inittab file.
                                      Boot init starts the process, waits
                                      for its termination, and, when it
                                      dies, does not restart the process.

                    initdefault       An entry with this action is only
                                      scanned when boot init is initially
                                      invoked.  Boot init uses this entry,
                                      if it exists, to determine which run
                                      level to enter initially.  It does
                                      this by taking the highest run level
                                      specified in the rstate field and
                                      using that as its initial state.  If
                                      the rstate field is empty, boot init
                                      enters run level 6.

                                      The initdefault entry cannot specify
                                      that boot init start in the single-
                                      user state.  Additionally, if boot
                                      init does not find an initdefault
                                      entry in inittab, it requests an
                                      initial run level from the user at
                                      boot time.

                    off               If the process associated with this
                                      entry is currently running, send the
                                      warning signal (SIGTERM) and wait 20
                                      seconds before forcibly terminating
                                      the process via the kill signal
                                      (SIGKILL).  If the process is
                                      nonexistent, ignore the entry.

                    once              When boot init enters a run level
                                      that matches the entry's rstate,
                                      start the process and do not wait for
                                      its termination.  When it dies, do
                                      not restart the process.  If boot
                                      init enters a new run level but the
                                      process is still running from a
                                      previous run level change, the
                                      process is not restarted.

                    ondemand          This instruction is really a synonym
                                      for the respawn action.  It is
                                      functionally identical to respawn but
                                      is given a different keyword in order
                                      to divorce its association with run
                                      levels.  This is used only with the
                                      a, b, or c values described in the
                                      rstate field.

                    powerfail         Execute the process associated with
                                      this entry only when boot init
                                      receives a power-fail signal (SIGPWR
                                      see signal(5)).

                    powerwait         Execute the process associated with
                                      this entry only when boot init
                                      receives a power-fail signal (SIGPWR)
                                      and wait until it terminates before
                                      continuing any processing of inittab.

                    respawn           If the process does not exist, start
                                      the process; do not wait for its
                                      termination (continue scanning the
                                      inittab file).  When it dies, restart
                                      the process.  If the process
                                      currently exists, do nothing and
                                      continue scanning the inittab file.

                    sysinit           Entries of this type are executed
                                      before boot init tries to access the
                                      console.  It is expected that this
                                      entry will be only used to initialize
                                      devices on which boot init might
                                      attempt to obtain run level
                                      information.  These entries are
                                      executed and waited for before
                                      continuing.

                    wait              When boot init enters the run level
                                      that matches the entry's rstate,
                                      start the process and wait for its
                                      termination.  Any subsequent reads of
                                      the inittab file while boot init is
                                      in the same run level cause boot init
                                      to ignore this entry.

          process   This is a sh command to be executed.  The entire
                    process field is prefixed with exec and passed to a
                    forked sh as "sh -c 'exec command'".  For this reason,
                    any sh syntax that can legally follow exec can appear
                    in the process field.  Comments can be inserted by
                    using the ; #comment syntax.

WARNINGS
     The use of a four-character id is strongly recommended.  Many pty
     servers use the last two characters of the pty name as an id.  If an
     id chosen by a pty server collides with one used in the inittab file,
     the /etc/utmp file can become corrupted.  A corrupt /etc/utmp file can
     cause commands such as who to report inaccurate information.

FILES
     /etc/inittab        File of processes dispatched by boot init.

SEE ALSO
     sh(1), getty(1M), exec(2), open(2), signal(5).