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OpenDarwin 7.2.1 - man page for init (opendarwin section 8)

INIT(8) 			   BSD 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 opera-
     tion.  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 pro-
     gram 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.  Security levels are defined as follows:

     -1    Permanently insecure mode - always run system in level 0 mode.

     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 - immutable and append-only flags may not be changed; disks for mounted
	   filesystems, /dev/mem, and /dev/kmem are read-only.	The settimeofday(2) system call
	   can only advance the time.

     2	   Highly secure mode - same as secure mode, plus disks are always read-only 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.

     Normally, the system runs in level 0 mode while single user and in level 1 mode while multi-
     user.  If the level 2 mode is desired while running multiuser, it can be set in the startup
     script /etc/rc using sysctl(8).  If it is desired to run the system in level 0 mode while
     multiuser, the administrator must build a kernel with the variable securelevel defined in
     the file /sys/compile/MACHINE/param.c and initialize it to -1.

     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
     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 file.  The cycle is then restarted by init execut-
     ing a new getty for the line.

     Line status (on, off, secure, getty, or window information) may be changed in the ttys file
     without a reboot by sending the signal SIGHUP to init with the command ``kill -s HUP 1''.
     On receipt of this signal, init re-reads the ttys file.  When a line is turned off in ttys,
     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 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,
     init will not do anything at all to that line.  However, it will complain that the relation-
     ship between lines in the ttys file and records in the utmp 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'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 automati-
     cally.  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 ter-
     minal 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.
     /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.

     login(1), kill(1), sh(1), ttys(5), crash(8), getty(8), rc(8), reboot(8), halt(8),

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

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

4th Berkeley Distribution		   May 26, 1995 		4th Berkeley Distribution

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