| INIT(8) | System Manager's Manual | INIT(8) |
init — process
control initialization
init |
[-fs] |
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 operation.
The kernel may pass the following options to
init, usually when requested by the
boot(8) program:
-f-sSingle-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 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
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) 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).
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.
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)
An init command appeared in
Version 1 AT&T UNIX.
| January 16, 2018 | OpenBSD-current |