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INIT(8)                 FreeBSD System Manager's Manual                INIT(8)

NAME
     init - process control initialization

SYNOPSIS
     init
     init [0 | 1 | 6 | c | q]

DESCRIPTION
     The init program is the last stage of the boot process.  It normally runs
     the automatic reboot sequence as described in rc(8), and if this
     succeeds, begins multi-user operation.  If the reboot scripts fail, init
     commences single-user operation by giving the super-user a shell on the
     console.  The init program may be passed parameters from the boot program
     to prevent the system from going multi-user and to instead execute a
     single-user shell without starting the normal daemons.  The system is
     then quiescent for maintenance work and may later be made to go to multi-
     user by exiting the single-user shell (with ^D).  This causes init to run
     the /etc/rc start up command file in fastboot mode (skipping disk
     checks).

     If the console entry in the ttys(5) file is marked ``insecure'', then
     init will require that the super-user password be entered before the
     system will start a single-user shell.  The password check is skipped if
     the console is marked as ``secure''.

     The kernel runs with four different levels of security.  Any super-user
     process can raise the security level, but no process can lower it.  The
     security levels are:

     -1    Permanently insecure mode - always run the system in level 0 mode.
           This is the default initial value.

     0     Insecure mode - immutable and append-only flags may be turned off.
           All devices may be read or written subject to their permissions.

     1     Secure mode - the system immutable and system append-only flags may
           not be turned off; disks for mounted filesystems, /dev/mem, and
           /dev/kmem may not be opened for writing; kernel modules (see
           kld(4)) may not be loaded or unloaded.

     2     Highly secure mode - same as secure mode, plus disks may not be
           opened for writing (except by mount(2)) whether mounted or not.
           This level precludes tampering with filesystems by unmounting them,
           but also inhibits running newfs(8) while the system is multi-user.

           In addition, kernel time changes are restricted to less than or
           equal to one second.  Attempts to change the time by more than this
           will log the message ``Time adjustment clamped to +1 second''.

     3     Network secure mode - same as highly secure mode, plus IP packet
           filter rules (see ipfw(8) and ipfirewall(4)) cannot be changed and
           dummynet(4) configuration cannot be adjusted.

     If the security level is initially nonzero, then init leaves it
     unchanged.  Otherwise, init raises the level to 1 before going multi-user
     for the first time.  Since the level can not be reduced, it will be at
     least 1 for subsequent operation, even on return to single-user.  If a
     level higher than 1 is desired while running multi-user, it can be set
     before going multi-user, e.g., by the startup script rc(8), using
     sysctl(8) to set the ``kern.securelevel'' variable to the required
     security level.

     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, unless the first field refers to a device in
     /dev which is not configured.  The first field is supplied as the final
     argument to the command.  This command is usually getty(8); getty opens
     and initializes the tty line and executes the login(1) program.  The
     login 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) file of current users and records the logout in the
     wtmp(5) file.  The cycle is then restarted by init executing a new getty
     for the line.

     Init can also be used to keep arbitrary daemons running, automatically
     restarting them if they die.  In this case, the first field in the
     ttys(5) file must not reference the path to a configured device node and
     will be passed to the daemon as the final argument on its command line.
     This is similar to the facility offered in the AT&T System V UNIX
     /etc/inittab.

     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 -HUP 1''.  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 the command specified
     in the second field.  If the command 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 -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 processes and allow the system to slowly die
     away, if it is sent a terminal stop (TSTP) signal, i.e. ``kill -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).

     Init will terminate all possible processes (again, it will not wait for
     deadlocked processes) and reboot the machine if sent the interrupt (INT)
     signal, i.e. ``kill -INT 1''.  This is useful for shutting the machine
     down cleanly from inside the kernel or from X when the machine appears to
     be hung.

     Init will do the same, except it will halt the machine if sent the user
     defined signal 1 (USR1), or will halt and turn the power off (if hardware
     permits) if sent the user defined signal 2 (USR2).

     When shutting down the machine, init will try to run the /etc/rc.shutdown
     script.  This script can be used to cleanly terminate specific programs
     such as innd (the InterNetNews server).

     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, the system will panic with the message ``panic: init died
     (signal %d, exit %d)''.

     If run as a user process as shown in the second synopsis line, init will
     emulate AT&T System V UNIX behavior, i.e. super-user can specify the
     desired run-level on a command line, and init will signal the original
     (PID 1) init as follows:

     Run-level    Signal     Action
     Cm 0         SIGUSR2    Halt and turn the power off
     1            SIGTERM    Go to single-user mode
     6            SIGINT     Reboot the machine
     c            SIGTSTP    Block further logins
     q            SIGHUP     Rescan the ttys(5) file

DIAGNOSTICS
     getty repeating too quickly on port %s, sleeping.  A process being
     started to service a line is exiting quickly each time it is started.
     This is often caused by a ringing or noisy terminal line.  Init will
     sleep for 30 seconds, then continue trying to start the process.

     some processes would not die; ps axl advised.  A process is hung and
     could not be killed when the system was shutting down.  This condition is
     usually caused by a process that is stuck in a device driver because of a
     persistent device error condition.

FILES
     /dev/console      system console device
     /dev/tty*         terminal ports found in ttys(5)
     /var/run/utmp     record of current users on the system
     /var/log/wtmp     record of all logins and logouts
     /etc/ttys         the terminal initialization information file
     /etc/rc           system startup commands
     /etc/rc.shutdown  system shutdown commands

SEE ALSO
     kill(1), login(1), sh(1), dummynet(4), ipfirewall(4), kld(4), ttys(5),
     crash(8), getty(8), halt(8), ipfw(8), rc(8), reboot(8), shutdown(8),
     sysctl(8)

HISTORY
     An init command appeared in Version 6 AT&T UNIX.

CAVEATS
     Systems without sysctl behave as though they have security level -1.

     Setting the security level above 1 too early in the boot sequence can
     prevent fsck(8) from repairing inconsistent filesystems.  The preferred
     location to set the security level is at the end of /etc/rc after all
     multi-user startup actions are complete.

FreeBSD 11.0-PRERELEASE         April 18, 1994         FreeBSD 11.0-PRERELEASE

NAME | SYNOPSIS | DESCRIPTION | DIAGNOSTICS | FILES | SEE ALSO | HISTORY | CAVEATS

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