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NetBSD 6.1.5 - man page for init (netbsd section 8)

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

NAME
     init -- process control initialization

SYNOPSIS
     init

DESCRIPTION
     The init program is the last stage of the boot process (after the kernel loads and initial-
     izes all the devices).  It normally begins multi-user operation.

     The following table describes the state machine used by init:

     1.   Single user shell.  init may be passed -s 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.  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).

     2.   Multi-user boot (default operation).	Executes /etc/rc (see rc(8)).  If this was the
	  first state entered (as opposed to entering here after state 1), then /etc/rc will be
	  invoked with its first argument being 'autoboot'.  If /etc/rc exits with a non-zero
	  (error) exit code, commence single user operation by giving the super-user a shell on
	  the console by going to state 1 (single user).  Otherwise, proceed to state 3.

	  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.

     3.   Set up ttys as specified in ttys(5).	See below for more information.  On completion,
	  continue to state 4.	If we did chroot in state 2, each getty(8) process will be run in
	  the same chroot(2) path as in 2 (that is, the value of ``init.root'' sysctl is not re-
	  read).

     4.   Multi-user operation.  Depending upon the signal received, change state appropriately;
	  on SIGTERM, go to state 7; on SIGHUP, go to state 5; on SIGTSTP, go to state 6.

     5.   Clean-up mode; re-read ttys(5), killing off the controlling processes on lines that are
	  now 'off', and starting processes that are newly 'on'.  On completion, go to state 4.

     6.   'Boring' mode; no new sessions.  Signals as per state 4.

     7.   Shutdown mode.  Send 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's found to be missing.  Type of the node is string capable of holding full path-
     name, 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 sig-
     nal 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 recom-
     mended.

     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 automati-
     cally.  If, at bootstrap time, the init process cannot be located, or exits during its ini-
     tialisation, 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.

FILES
     /dev/console	System console device.
     /dev/tty*		Terminal ports found in ttys(5).
     /var/run/utmp{,x}	Record of current users on the system.
     /var/log/wtmp{,x}	Record of all logins and logouts.
     /etc/ttys		The terminal initialization information file.
     /etc/rc		System startup commands.

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 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.

SEE ALSO
     config(1), kill(1), login(1), sh(1), options(4), ttys(5), getty(8), halt(8), MAKEDEV(8),
     MAKEDEV.local(8), mount_mfs(8), mount_tmpfs(8), rc(8), reboot(8), rescue(8), shutdown(8),
     sysctl(8), secmodel_bsd44(9), secmodel_securelevel(9)

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

BSD					November 10, 2008				      BSD
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