The
init
program
is the last stage of the boot process.
It normally executes the sequence of events described in
rc(8),
and if this succeeds, begins multi-user operation.
If the boot 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 before 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 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),
run
/etc/rc.shutdown,
and halt the machine if user-defined signal 1
(USR1)
or user-defined signal 2
.Pd Dv USR2
is received.
/etc/rc.shutdown
can specify that a powerdown is requested.
Alternatively,
USR2
specifically requests a powerdown.
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
/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
DIAGNOSTICS
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".
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.