INIT(8) System Manager's Manual INIT(8)
init - process control initialization
The init program is the last stage of the boot process. It normally
executes the sequence of events described in rc(8) and begins multi-user
The kernel may pass the following options to init, usually when requested
by the boot(8) program:
-f Activate fastboot mode. This is not currently supported by the
OpenBSD kernel. Instead, use the /fastboot file as explained in
the rc(8) manual.
-s Boot directly into single-user mode.
Single-user mode is also entered if the boot scripts fail.
In single-user mode, the rc(8) script is not run and normal daemons are
not started, but instead a super-user shell is started on the system
console. If the console entry in the ttys(5) file does not contain the
"secure" flag, 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".
In single-user mode, the system is 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 rc(8) startup command file in fastboot
mode (skipping disk checks).
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 be modified
via the /etc/rc.securelevel script.
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 executing 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 relationship between lines in the ttys
file and records in the utmp file is out of sync, so this practice is not
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
init will cease creating new getty(8) 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)
init will terminate multi-user operations, kill all getty(8), and run
/etc/rc.shutdown if a user-defined signal 1 (USR1), user-defined signal 2
(USR2), or interrupt (INT) signal is received. Following this, USR1 will
halt the system; USR2 will request a powerdown; and INT will cause a
reboot. /etc/rc.shutdown can specify that a powerdown is requested
instead of the action specified by the signal.
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)".
When init spawns a process it sets the process priority, umask, and
resource limits based on /etc/login.conf. When starting the rc(8) files,
the login class "daemon" is used. When starting a window system or
getty(8), the login class "default" is used. No resource changes are
made when entering single-user mode.
/dev/console system console device
/dev/tty* terminal ports found in ttys
/etc/rc system startup commands
/etc/rc.securelevel commands that run before the security level changes
/etc/rc.shutdown script run at shutdown time
/etc/ttys terminal initialization information file
/fastboot tells rc(8) not to run fsck(8) during the next boot
/var/run/utmp record of users currently logged in
/var/log/wtmp record of all logins and logouts
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.
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 1 AT&T UNIX.
OpenBSD 6.2 October 6, 2016 OpenBSD 6.2
[Unix Hosting |
[Engineering & Automation |
Software Development |