| INIT(8) | System Manager's Manual | INIT(8) | 
init —
| init | [ -s] | 
init program is the last stage of the boot process.
  It normally begins multi-user operation.
init is executed automatically by the
    kernel, after the kernel has initialised all devices and mounted the root
    file system. The kernel may try multiple possible paths for
    init, including /sbin/init,
    /sbin/oinit, /sbin/init.bak,
    and /rescue/init.
The following table describes the state machine used by
    init:
-s option to
      init to prevent the system from going multi-user
      and to instead execute a single user shell without starting the normal
      daemons. If the kernel is in a secure mode, init
      will downgrade it to securelevel 0 (insecure mode). The system is then
      quiescent for maintenance work and may later be made to go to state 2
      (multi-user) by exiting the single-user shell (with ^D).If value of the “init.root” sysctl node is not equal to / at this point, the /etc/rc process will be run inside a chroot(2) indicated by sysctl with the same error handling as above.
If the administrator has not set the security level to -1 to
        indicate that the kernel should not run multiuser in secure mode, and
        the /etc/rc script has not set a higher level of
        security than level 1, then init will put the
        kernel into securelevel mode 1. See
        rc.conf(5) and
        secmodel_securelevel(9)
        for more information.
SIGTERM, go to state 7; on
      SIGHUP, go to state 5; on
      SIGTSTP, go to state 6.SIGHUP to all controlling
      processes, reap the processes for 30 seconds, and then go to state 1
      (single user); warning if not all the processes died.If the ‘console’ entry in the
    ttys(5) file is marked
    “insecure”, then init will require
    that the superuser password be entered before the system will start a
    single-user shell. The password check is skipped if the
    ‘console’ is marked as “secure”.
It should be noted that while init has the
    ability to start multi-user operation inside a
    chroot(2) environment, the
    init process itself will always run in the
    “original root directory”. This also implies that single-user
    mode is always started in the original root, giving the possibility to
    create multi-user sessions in different root directories over time. The
    “init.root” sysctl node is fabricated by
    init at startup and re-created any time it is found
    to be missing. Type of the node is string capable of holding full pathname,
    and is only accessible by the superuser (unless explicitly destroyed and
    re-created with different specification).
In multi-user operation, init maintains
    processes for the terminal ports found in the file
    ttys(5).
    init reads this file, and executes the command found
    in the second field. This command is usually
    getty(8); it opens and
    initializes the tty line and executes the
    login(1) program. The
    login(1) program, when a valid
    user logs in, executes a shell for that user. When this shell dies, either
    because the user logged out or an abnormal termination occurred (a signal),
    the init program wakes up, deletes the user from the
    utmp(5) and
    utmpx(5) files of current users
    and records the logout in the
    wtmp(5) and
    wtmpx(5) files. The cycle is
    then restarted by init executing a new
    getty(8) for the line.
Line status (on, off, secure, getty, or window information) may be
    changed in the ttys(5) file
    without a reboot by sending the signal SIGHUP to
    init with the command “kill
    -s HUP 1”. This is referenced in the table above as state 5.
    On receipt of this signal, init re-reads the
    ttys(5) file. When a line is
    turned off in ttys(5),
    init will send a SIGHUP
    signal to the controlling process for the session associated with the line.
    For any lines that were previously turned off in the
    ttys(5) file and are now on,
    init executes a new
    getty(8) to enable a new login.
    If the getty or window field for a line is changed, the change takes effect
    at the end of the current login session (e.g., the next time
    init starts a process on the line). If a line is
    commented out or deleted from
    ttys(5),
    init will not do anything at all to that line.
    However, it will complain that the relationship between lines in the
    ttys(5) file and records in the
    utmp(5) file is out of sync, so
    this practice is not recommended.
init will terminate multi-user operations
    and resume single-user mode if sent a terminate
    (TERM) signal, for example,
    “kill -s TERM 1”. If there are
    processes outstanding that are deadlocked (because of hardware or software
    failure), init will not wait for them all to die
    (which might take forever), but will time out after 30 seconds and print a
    warning message.
init will cease creating new
    getty(8)'s and allow the system
    to slowly die away, if it is sent a terminal stop
    (TSTP) signal, i.e., “kill
    -s TSTP 1”. A later hangup will resume full multi-user
    operations, or a terminate will start a single user shell. This hook is used
    by reboot(8) and
    halt(8).
The role of init is so critical that if it
    dies, the system will reboot itself automatically. If, at bootstrap time,
    the init process cannot be located, or exits during
    its initialisation, the system will panic with the message “panic:
    init died (signal %d, exit %d)”.
If /dev/console does not exist,
    init will cd to /dev and run
    “MAKEDEV -MM init”.
    MAKEDEV(8) will use
    mount_tmpfs(8) or
    mount_mfs(8) to create a
    memory file system mounted over /dev that contains
    the standard devices considered necessary to boot the system.
init command appeared in
  Version 1 AT&T UNIX.
| September 1, 2019 | NetBSD 10.0 |