init(8)

NAME

init - process control initialization

SYNOPSIS

init
init [0 | 1 | 6 | c | q]

DESCRIPTION

The init utility is the last stage of the boot process. It

normally runs
the automatic reboot sequence as described in rc(8), and if

this succeeds, begins multi-user operation. If the reboot scripts

fail, init
commences single-user operation by giving the super-user a

shell on the
console. The init utility 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

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 start up command file in fastboot mode (skipping

disk checks).

If the console entry in the ttys(5) file is marked ``inse

cure'', then
init will require that the super-user password be entered

before the system will start a single-user shell. The password check is

skipped if the
console is marked as ``secure''.

The kernel runs with five different levels of security. Any

super-user
process can raise the security level, but no process can

lower it. The
security levels are:

-1 Permanently insecure mode - always run the system in

level 0 mode.

This is the default initial value.

0 Insecure mode - immutable and append-only flags may be

turned off.

All devices may be read or written subject to their

permissions.

1 Secure mode - the system immutable and system append

only flags may

not be turned off; disks for mounted file systems,

/dev/mem,
/dev/kmem and /dev/io (if your platform has it) may

not be opened
for writing; kernel modules (see kld(4)) may not be

loaded or
unloaded.

2 Highly secure mode - same as secure mode, plus disks

may not be

opened for writing (except by mount(2)) whether mount

ed or not.
This level precludes tampering with file systems by

unmounting
them, but also inhibits running newfs(8) while the

system is multiuser.

In addition, kernel time changes are restricted to

less than or
equal to one second. Attempts to change the time by

more than this
will log the message ``Time adjustment clamped to +1

second''.

3 Network secure mode - same as highly secure mode, plus

IP packet

filter rules (see ipfw(8), ipfirewall(4) and pfctl(8))

cannot be
changed and dummynet(4) or pf(4) configuration cannot

be adjusted.

If the security level is initially nonzero, then init leaves

it
unchanged. Otherwise, init raises the level to 1 before go

ing multi-user
for the first time. Since the level cannot be reduced, it

will be at
least 1 for subsequent operation, even on return to single

user. If a
level higher than 1 is desired while running multi-user, it

can be set
before going multi-user, e.g., by the startup script rc(8),

using
sysctl(8) to set the kern.securelevel variable to the re

quired security
level.

If init is run in a jail, the security level of the ``host

system'' will
not be effected. Part of the information set up in the ker

nel to support
a jail is a per-jail ``securelevel'' setting. This allows

running a
higher security level inside of a jail than that of the host

system. See
jail(8) for more information about jails.

In multi-user operation, init maintains processes for the

terminal ports
found in the file ttys(5). The init utility reads this file

and executes
the command found in the second field, unless the first

field refers to a
device in /dev which is not configured. The first field is

supplied as
the final argument to the command. This command is usually

getty(8);
getty opens and initializes the tty line and executes the

login(1) program. The login program, when a valid user logs in, exe

cutes a shell for
that user. When this shell dies, either because the user

logged out or
an abnormal termination occurred (a signal), the init utili

ty wakes up,
deletes the user from the utmp(5) file of current users and

records the
logout in the wtmp(5) file. The cycle is then restarted by

init executing a new getty for the line.

The init utility can also be used to keep arbitrary daemons

running,
automatically restarting them if they die. In this case,

the first field
in the ttys(5) file must not reference the path to a config

ured device
node and will be passed to the daemon as the final argument

on its command line. This is similar to the facility offered in the

AT&T System V
UNIX /etc/inittab.

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 -HUP 1''. 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 previous

ly turned off
in the ttys(5) file and are now on, init executes the com

mand specified
in the second field. If the command 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 any

thing at all
to that line. However, it will complain that the relation

ship between
lines in the ttys(5) file and records in the utmp(5) file is

out of sync,
so this practice is not recommended.

The init utility will terminate multi-user operations and

resume singleuser 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 sec

onds and print
a warning message.

The init utility will cease creating new processes 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-us

er operations,
or a terminate will start a single-user shell. This hook is

used by
reboot(8) and halt(8).

The init utility will terminate all possible processes

(again, it will
not wait for deadlocked processes) and reboot the machine if

sent the
interrupt (INT) signal, i.e. ``kill -INT 1''. This is use

ful for shutting the machine down cleanly from inside the kernel or from

X when the
machine appears to be hung.

The init utility will do the same, except it will halt the

machine if
sent the user defined signal 1 (USR1), or will halt and turn

the power
off (if hardware permits) if sent the user defined signal 2

(USR2).

When shutting down the machine, init will try to run the

/etc/rc.shutdown
script. This script can be used to cleanly terminate spe

cific programs
such as innd (the InterNetNews server). If this script does

not terminate within 120 seconds, init will terminate it. The timeout

can be configured via the sysctl(8) variable

kern.init_shutdown_timeout.

The role of init is so critical that if it dies, the system

will reboot
itself automatically. If, at bootstrap time, the init pro

cess cannot be
located, the system will panic with the message ``panic:

init died
(signal %d, exit %d)''.

If run as a user process as shown in the second synopsis

line, init will
emulate AT&T System V UNIX behavior, i.e., super-user can

specify the
desired run-level on a command line, and init will signal

the original
(PID 1) init as follows:

Run-level Signal Action 0 SIGUSR2 Halt and turn the power off
1 SIGTERM Go to single-user mode
6 SIGINT Reboot the machine
c SIGTSTP Block further logins
q SIGHUP Rescan the ttys(5) file

FILES

/dev/console system console device
/dev/tty* terminal ports found in ttys(5)
/var/run/utmp record of current users on the system
/var/log/wtmp record of all logins and logouts
/etc/ttys the terminal initialization information

file
/etc/rc system startup commands
/etc/rc.shutdown system shutdown 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 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.

SEE ALSO

kill(1), login(1), sh(1), dummynet(4), ipfirewall(4),

kld(4), pf(4),
ttys(5), crash(8), getty(8), halt(8), ipfw(8), jail(8),

pfctl(8), rc(8),
reboot(8), shutdown(8), sysctl(8)

HISTORY

An init utility appeared in Version 6 AT&T UNIX.

CAVEATS

Systems without sysctl(8) behave as though they have securi

ty level -1.

Setting the security level above 1 too early in the boot se

quence can
prevent fsck(8) from repairing inconsistent file systems.

The preferred
location to set the security level is at the end of /etc/rc

after all
multi-user startup actions are complete.

BSD September 15, 2005

BSD