init - process control initialization
The init program is the last stage of the boot process. It
the automatic reboot sequence as described in reboot(8), and
if this succeeds,
begins multi-user operation. If the reboot scripts
commences single-user operation by giving the superuser a
shell on the
console. The init program may be passed parameters from the
to prevent the system from going multi-user and to instead
execute a single-user
shell without starting the normal daemons.
The following parameters may be passed from the boot program:
-f Activate fastboot mode.
-s Boot directly into single user mode.
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
causes init to run the /etc/rc startup command file in fastboot mode
(skipping disk checks).
If the console entry in the ttys(5) file does not contain
flag, then init will require that the superuser password be
the system will start a single-user shell. The password check is
skipped if the console is marked as ``secure''.
The kernel securelevel(7) is normally set to 0 while in single-user mode,
and raised to 1 when the system begins multi-user operations. This action
will not take place if the securelevel is -1, and can
via the /etc/rc.securelevel script.
In multi-user operation, init maintains processes for the
found in the file ttys(5). init reads this file, and executes the command
found in the second field. This command is usually
opens and initializes the tty line and executes the login
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
termination occurred (a signal), the init program wakes up,
user from the utmp(5) file of current users and records the
logout in the
wtmp file. The cycle is then restarted by init executing a
new getty for
Line status (on, off, secure, getty, or window information)
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
re-reads the ttys file. When a line is turned off in ttys,
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,
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.
will complain that the relationship between lines in the
ttys file and
records in the utmp file is out of sync, so this practice is
init will terminate multi-user operations and resume singleuser mode if
sent a terminate (TERM) signal, for example, ``kill -s TERM
there are processes outstanding that are deadlocked (because
or software failure), init will not wait for them all to die
take forever), but will time out after 30 seconds and print
init will cease creating new getty's and allow the system to
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
init will terminate multi-user operations, kill all getty's,
/etc/rc.shutdown, and halt the machine if user-defined signal 1 (USR1) is
The role of init is so critical that if it dies, the system
itself automatically. If, at bootstrap time, the init process cannot be
located, the system will panic with the message ``panic:
(signal %d, exit %d)''.
When init spawns a process it sets the process priority,
umask, and resource
limits based on /etc/login.conf. When starting the
the login class ``daemon'' is used. When starting a window
getty(8), the login class ``default'' is used. No resource
made when entering single user mode.
/dev/console system console device
/dev/tty* terminal ports found in ttys
/var/run/utmp record of users currently logged in
/var/log/wtmp record of all logins and logouts
/etc/ttys terminal initialization information
/etc/rc system startup commands
/etc/rc.securelevel commands that run before the security
/etc/rc.shutdown script run at shutdown time
getty repeating too quickly on port %s, sleeping A process
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
could not be killed when the system was shutting down. This
usually caused by a process that is stuck in a device driver
because of a
persistent device error condition.
kill(1), login(1), sh(1), fbtab(5), login.conf(5), ttys(5),
securelevel(7), crash(8), getty(8), halt(8), rc(8), rc.shutdown(8),
An init command appeared in Version 6 AT&T UNIX.
OpenBSD 3.6 May 26, 1995
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