inittab

inittab - File that supplies scripts to init.

 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).