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
operation.
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
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.
- /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 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)
An
init command appeared in
Version 1 AT&T UNIX.
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