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

     init - process control initialization


     The init program is the last stage of the boot process.  It normally runs
     the automatic reboot sequence as described in reboot(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

     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''.

     The kernel runs with four different levels of security.  Any superuser
     process can raise the security level, but only init 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.

     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.

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

     If the security level is initially -1, then init leaves it unchanged.
     Otherwise, init arranges to run the system in level 0 mode while single
     user and in level 1 mode while multiuser.  If level 2 mode is desired
     while running multiuser, it can be set while single user, e.g., in the
     startup script /etc/rc, 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.  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.

     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 a new getty 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 -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

     Init will cease creating new getty's 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.

     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)''.

     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 10
     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.

     /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
                    system shutdown commands

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

     A init command appeared in Version 6 AT&T UNIX.

     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.

BSD 4                           April 18, 1994                           BSD 4


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