INIT(8) BSD System Manager's Manual INIT(8)NAMEinit - process control initialisation
SYNOPSISinit [-fs]
DESCRIPTION
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 operation. If the reboot scripts fail, init
commences single-user operation by giving the superuser a shell on the
console. The init program may be passed parameters 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.
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 ^D). This
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 the "secure"
flag, then init will require that the superuser password be entered be-
fore 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 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 initialises 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 termi-
nation 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 -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 recommended.
init will terminate multi-user operations and resume single-user mode if
sent a terminate (TERM) signal, for example, "kill -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 gettys and allow the system to slowly die
away, if it is sent a terminal stop (TSTP) signal, i.e., "kill -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 gettys, run /etc/rc
shutdown, and halt the machine if user-defined signal 1 (USR1) is re-
ceived, e.g. by "kill -USR1 1".
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)".
RESOURCES
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.
FILES
/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 initialisation information file
/etc/rc system startup commands
/etc/rc.securelevel commands that run before the security level changes
/etc/rc.shutdown script run at shutdown time via /etc/rc
/var/db/host.random where 2 KiB entropy are stored on SIGUSR1
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 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.
SEE ALSOkill(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)HISTORY
An init command appeared in Version 6 AT&T UNIX.
MirOS BSD #10-current February 19, 2011 1
