sbin/init/init.8

.\"	$MirOS: src/sbin/init/init.8,v 1.2 2011/02/19 14:41:38 tg Exp $
.\"	$OpenBSD: init.8,v 1.33 2004/02/24 13:14:29 jmc Exp $
.\"	$NetBSD: init.8,v 1.6 1995/03/18 14:56:31 cgd Exp $
.\"
.\" Copyright (c) 1980, 1991, 1993
.\"	The Regents of the University of California.  All rights reserved.
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.\" This code is derived from software contributed to Berkeley by
.\" Donn Seeley at Berkeley Software Design, Inc.
.\"
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.\" modification, are permitted provided that the following conditions
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.\"     @(#)init.8	8.6 (Berkeley) 5/26/95
.\"
.Dd $Mdocdate: February 19 2011 $
.Dt INIT 8
.Os
.Sh NAME
.Nm init
.Nd process control initialisation
.Sh SYNOPSIS
.Nm init
.Op Fl fs
.Sh DESCRIPTION
The
.Nm
program
is the last stage of the boot process.
It normally runs the automatic reboot sequence as described in
.Xr reboot 8 ,
and if this succeeds, begins multi-user operation.
If the reboot scripts fail,
.Nm
commences single-user operation by giving
the superuser a shell on the console.
The
.Nm
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.
.Pp
The following parameters may be passed from the boot program:
.Bl -tag -width Ds
.It Fl f
Activate fastboot mode.
.It Fl s
Boot directly into single user mode.
.El
.Pp
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
.Nm
to run the
.Pa /etc/rc
startup command file in fastboot mode (skipping disk checks).
.Pp
If the
.Ar console
entry in the
.Xr ttys 5
file does not contain the
.Dq secure
flag, then
.Nm
will require that the superuser password be
entered before the system will start a single-user shell.
The password check is skipped if the
.Ar console
is marked as
.Dq secure .
.Pp
The kernel
.Xr 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
.Pa /etc/rc.securelevel
script.
.Pp
In multi-user operation,
.Nm
maintains
processes for the terminal ports found in the file
.Xr ttys 5 .
.Nm
reads this file, and executes the command found in the second field.
This command is usually
.Xr getty 8 ;
.Em getty
opens and initialises the tty line
and
executes the
.Em login
program.
The
.Em 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
.Nm
program wakes up, deletes the user
from the
.Xr utmp 5
file of current users and records the logout in the
.Em wtmp
file.
The cycle is
then restarted by
.Nm
executing a new
.Em getty
for the line.
.Pp
Line status (on, off, secure, getty, or window information)
may be changed in the
.Em ttys
file without a reboot by sending the signal
.Dv SIGHUP
to
.Nm
with the command
.Dq Li "kill \-HUP 1" .
On receipt of this signal,
.Nm
re-reads the
.Em ttys
file.
When a line is turned off in
.Em ttys ,
.Nm
will send a
.Dv SIGHUP
signal to the controlling process
for the session associated with the line.
For any lines that were previously turned off in the
.Em ttys
file and are now on,
.Nm
executes a new
.Em 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
.Nm
starts a process on the line).
If a line is commented out or deleted from
.Em ttys ,
.Nm
will not do anything at all to that line.
However, it will complain that the relationship between lines
in the
.Em ttys
file and records in the
.Em utmp
file is out of sync,
so this practice is not recommended.
.Pp
.Nm
will terminate multi-user operations and resume single-user mode
if sent a terminate
.Pq Dv TERM
signal, for example,
.Dq Li "kill \-TERM 1" .
If there are processes outstanding that are deadlocked (because of
hardware or software failure),
.Nm
will not wait for them all to die (which might take forever), but
will time out after 30 seconds and print a warning message.
.Pp
.Nm
will cease creating new
.Xr getty Ns s
and allow the system to slowly die away, if it is sent a terminal stop
.Pq Dv TSTP
signal, i.e.,
.Dq Li "kill \-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
.Xr reboot 8
and
.Xr halt 8 .
.Pp
.Nm
will terminate multi-user operations, kill all
.Xr getty Ns s ,
run
.Pa /etc/rc Ic shutdown ,
and halt the machine if user-defined signal 1
.Pq Dv USR1
is received, e.g. by
.Dq Li "kill \-USR1 1" .
.Pp
The role of
.Nm
is so critical that if it dies, the system will reboot itself
automatically.
If, at bootstrap time, the
.Nm
process cannot be located, the system will panic with the message
.Dq panic: "init died (signal %d, exit %d) .
.Sh RESOURCES
When
.Nm
spawns a process it sets the process priority, umask, and resource
limits based on
.Pa /etc/login.conf .
When starting the
.Xr rc 8
files, the login class
.Dq daemon
is used.
When starting a window system or
.Xr getty 8 ,
the login class
.Dq default
is used.
No resource changes are made when entering single user mode.
.Sh FILES
.Bl -tag -width /etc/rc.securelevel -compact
.It Pa /dev/console
system console device
.It Pa /dev/tty*
terminal ports found in
.Em ttys
.It Pa /var/run/utmp
record of users currently logged in
.It Pa /var/log/wtmp
record of all logins and logouts
.It Pa /etc/ttys
terminal initialisation information file
.It Pa /etc/rc
system startup commands
.It Pa /etc/rc.securelevel
commands that run before the security level changes
.It Pa /etc/rc.shutdown
script run at shutdown time via
.Pa /etc/rc
.It Pa /var/db/host.random
where 2 KiB entropy are stored on
.Dv SIGUSR1
.El
.Sh DIAGNOSTICS
.Bl -diag
.It "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.
.Em "Init will sleep for 10 seconds" ,
.Em "then continue trying to start the process" .
.Pp
.It "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.
.El
.Sh SEE ALSO
.Xr kill 1 ,
.Xr login 1 ,
.Xr sh 1 ,
.Xr fbtab 5 ,
.Xr login.conf 5 ,
.Xr ttys 5 ,
.Xr securelevel 7 ,
.Xr crash 8 ,
.Xr getty 8 ,
.Xr halt 8 ,
.Xr rc 8 ,
.Xr rc.shutdown 8 ,
.Xr reboot 8 ,
.Xr shutdown 8
.Sh HISTORY
An
.Nm
command appeared in
.At v6 .