INIT(8) BSD System Manager's Manual INIT(8)NAMEinit — process control initialization
SYNOPSISinitDESCRIPTION
The init program is the last stage of the boot process (after the kernel
loads and initializes all the devices). It normally begins multi-user
operation.
The following table describes the state machine used by init:
1. Single user shell. init may be passed -s 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. If the ker‐
nel is in a secure mode, init will downgrade it to securelevel 0
(insecure mode). The system is then quiescent for maintenance work
and may later be made to go to state 2 (multi-user) by exiting the
single-user shell (with ^D).
2. Multi-user boot (default operation). Executes /etc/rc (see rc(8)).
If this was the first state entered (as opposed to entering here
after state 1), then /etc/rc will be invoked with its first argument
being ‘autoboot’. If /etc/rc exits with a non-zero (error) exit
code, commence single user operation by giving the super-user a
shell on the console by going to state 1 (single user). Otherwise,
proceed to state 3.
If value of the “init.root” sysctl node is not equal to / at this
point, the /etc/rc process will be run inside a chroot(2) indicated
by sysctl with the same error handling as above.
If the administrator has not set the security level to -1 to indi‐
cate that the kernel should not run multiuser in secure mode, and
the /etc/rc script has not set a higher level of security than level
1, then init will put the kernel into securelevel mode 1. See
rc.conf(5) and secmodel_securelevel(9) for more information.
3. Set up ttys as specified in ttys(5). See below for more informa‐
tion. On completion, continue to state 4. If we did chroot in
state 2, each getty(8) process will be run in the same chroot(2)
path as in 2 (that is, the value of “init.root” sysctl is not re-
read).
4. Multi-user operation. Depending upon the signal received, change
state appropriately; on SIGTERM, go to state 7; on SIGHUP, go to
state 5; on SIGTSTP, go to state 6.
5. Clean-up mode; re-read ttys(5), killing off the controlling pro‐
cesses on lines that are now ‘off’, and starting processes that are
newly ‘on’. On completion, go to state 4.
6. ‘Boring’ mode; no new sessions. Signals as per state 4.
7. Shutdown mode. Send SIGHUP to all controlling processes, reap the
processes for 30 seconds, and then go to state 1 (single user);
warning if not all the processes died.
If the ‘console’ entry in the ttys(5) file is marked “insecure”, then
init will require that the superuser password be entered before the sys‐
tem will start a single-user shell. The password check is skipped if the
‘console’ is marked as “secure”.
It should be noted that while init has the ability to start multi-user
operation inside a chroot(2) environment, the init process itself will
always run in the “original root directory”. This also implies that sin‐
gle-user mode is always started in the original root, giving the possi‐
bility to create multi-user sessions in different root directories over
time. The “init.root” sysctl node is fabricated by init at startup and
re-created any time it's found to be missing. Type of the node is string
capable of holding full pathname, and is only accessible by the superuser
(unless explicitly destroyed and re-created with different specifica‐
tion).
In multi-user operation, init maintains processes for the terminal ports
found in the file ttys(5). init reads this file, and executes the com‐
mand found in the second field. This command is usually getty(8); it
opens and initializes the tty line and executes the login(1) program.
The login(1) 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) and utmpx(5) files of current users and
records the logout in the wtmp(5) and wtmpx(5) files. The cycle is then
restarted by init executing a new getty(8) for the line.
Line status (on, off, secure, getty, or window information) may be
changed in the ttys(5) file without a reboot by sending the signal SIGHUP
to init with the command “kill -s HUP 1”. This is referenced in the ta‐
ble above as state 5. On receipt of this signal, init re-reads the
ttys(5) file. When a line is turned off in ttys(5), 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(5)
file and are now on, init executes a new getty(8) 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(5), init will not do anything at all to that line. However, it
will complain that the relationship between lines in the ttys(5) file and
records in the utmp(5) file is out of sync, so this practice is not rec‐
ommended.
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)'s 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).
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, or exits during its initialisation, the system will panic with
the message “panic: init died (signal %d, exit %d)”.
If /dev/console does not exist, init will cd to /dev and run “MAKEDEV -MM
init”. MAKEDEV(8) will use mount_tmpfs(8) or mount_mfs(8) to create a
memory file system mounted over /dev that contains the standard devices
considered necessary to boot the system.
FILES
/dev/console System console device.
/dev/tty* Terminal ports found in ttys(5).
/var/run/utmp{,x} Record of current users on the system.
/var/log/wtmp{,x} Record of all logins and logouts.
/etc/ttys The terminal initialization information file.
/etc/rc System startup commands.
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 ALSOconfig(1), kill(1), login(1), sh(1), options(4), ttys(5), getty(8),
halt(8), MAKEDEV(8), MAKEDEV.local(8), mount_mfs(8), mount_tmpfs(8),
rc(8), reboot(8), rescue(8), shutdown(8), sysctl(8), secmodel_bsd44(9),
secmodel_securelevel(9)HISTORY
A init command appeared in Version 6 AT&T UNIX.
BSD November 10, 2008 BSD
