init program is the last stage of the
boot process. It normally executes the sequence of events described in
rc(8) and begins
The kernel may pass the following options to
init, usually when requested by the
- Activate fastboot mode. This is not currently supported by the OpenBSD kernel. Instead, use the /fastboot file as explained in the rc(8) manual.
- 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
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
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,
maintains processes for the terminal ports found in the file
init reads this file, and executes the command found
in the second field. This command is usually
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
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
init with the command “
-s HUP 1”. On receipt of this signal,
init re-reads the ttys file. When
a line is turned off in ttys,
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
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 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
init will not wait for them all to die
(which might take forever), but will time out after 30 seconds and print a
init will cease creating new
allow the system to slowly die away, if it is sent a terminal stop
TSTP) signal, i.e., “
-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).
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 (
signal is received. Following this,
USR1 will halt
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,
init process cannot be located, the system will
panic with the message “panic: init died (signal %d, exit
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
the login class “default” is used. No resource changes are
made when entering single-user mode.
- system console device
- terminal ports found in ttys
- system startup commands
- commands that run before the security level changes
- script run at shutdown time
- terminal initialization information file
- tells rc(8) not to run fsck(8) during the next boot
- record of users currently logged in
- 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 30 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), reboot(8), shutdown(8)
init command appeared in
Version 1 AT&T UNIX.