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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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.\"     @(#)init.8	8.3 (Berkeley) 4/18/94
.\" $FreeBSD: src/sbin/init/init.8,v 1.22.2.11 2003/05/03 22:19:20 keramida Exp $
.\"
.Dd September 11, 2019
.Dt INIT 8
.Os
.Sh NAME
.Nm init
.Nd process control initialization
.Sh SYNOPSIS
.Nm
.Nm
.Oo
.Cm 0 | 1 | 6 |
.Cm c | q
.Oc
.Sh DESCRIPTION
The
.Nm
utility
is the last stage of the boot process.
It normally runs the automatic reboot sequence as described in
.Xr rc 8 ,
and if this succeeds, begins multi-user operation.
If the reboot scripts fail,
.Nm
commences single-user operation by giving
the super-user a shell on the console.
The
.Nm
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
.Nm
to run the
.Pa /etc/rc
start up command file in fastboot mode (skipping disk checks).
.Pp
If the
.Em console
entry in the
.Xr ttys 5
file is marked
.Dq insecure ,
then
.Nm
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
.Em console
is marked as
.Dq secure .
.Pp
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:
.Bl -tag -width flag
.It Ic -1
Permanently insecure mode \- always run the system in level 0 mode.
This is the default initial value.
.It Ic 0
Insecure mode \- immutable and append-only flags may be turned off.
All devices may be read or written subject to their permissions.
.It Ic 1
Secure mode \- the system immutable and system append-only flags may not
be turned off;
disks for mounted file systems,
.Pa /dev/mem ,
and
.Pa /dev/kmem
may not be opened for writing;
kernel modules (see
.Xr kld 4 )
may not be loaded or unloaded.
.It Ic 2
Highly secure mode \- same as secure mode, plus disks may not be
opened for writing (except by
.Xr mount 2 )
whether mounted or not.
This level precludes tampering with file systems by unmounting them,
but also inhibits running
.Xr newfs 8
while the system is multi-user.
.Pp
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
.Dq Time adjustment clamped to +1 second .
.It Ic 3
Network secure mode \- same as highly secure mode, plus
IP packet filter rules (see
.Xr ipfw 8
and
.Xr ipfirewall 4 )
cannot be changed and
.Xr dummynet 4
configuration cannot be adjusted.
.El
.Pp
If the security level is initially nonzero, then
.Nm
leaves it unchanged.
Otherwise,
.Nm
raises the level to 1 before going 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
.Xr rc 8 ,
using
.Xr sysctl 8
to set the
.Va kern.securelevel
variable to the required security level.
.Pp
In multi-user operation,
.Nm
maintains
processes for the terminal ports found in the file
.Xr ttys 5 .
The
.Nm
utility reads this file and executes the command found in the second field,
unless the first field refers to a device in
.Pa /dev
which is not configured.
The first field is supplied as the final argument to the command.
This command is usually
.Xr getty 8 ;
.Nm getty
opens and initializes the tty line
and
executes the
.Xr login 1
program.
The
.Nm 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
utility wakes up, deletes the user
from the
.Xr utmpx 5
file of current users and records the logout in the
.Xr wtmpx 5
file.
The cycle is
then restarted by
.Nm
executing a new
.Nm getty
for the line.
.Pp
The
.Nm
utility can also be used to keep arbitrary daemons running,
automatically restarting them if they die.
In this case, the first field in the
.Xr ttys 5
file must not reference the path to a configured 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 V
.Pa /etc/inittab .
.Pp
Line status (on, off, secure, getty, or window information)
may be changed in the
.Xr ttys 5
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
.Xr ttys 5
file.
When a line is turned off in
.Xr ttys 5 ,
.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
.Xr ttys 5
file and are now on,
.Nm
executes the command 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
.Nm
starts a process on the line).
If a line is commented out or deleted from
.Xr ttys 5 ,
.Nm
will not do anything at all to that line.
However, it will complain that the relationship between lines
in the
.Xr ttys 5
file and records in the
.Xr utmpx 5
file is out of sync,
so this practice is not recommended.
.Pp
The
.Nm
utility 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
The
.Nm
utility will cease creating new processes
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
The
.Nm
utility will terminate all possible processes (again, it will not wait
for deadlocked processes) and reboot the machine if sent the interrupt
.Pq Dv INT
signal, i.e.\&
.Dq Li "kill \-INT 1".
This is useful for shutting the machine down cleanly from inside the kernel
or from X when the machine appears to be hung.
.Pp
The
.Nm
utility will do the same, except it will halt the machine if sent
the user defined signal 1
.Pq Dv USR1 ,
or will halt and turn the power off (if hardware permits) if sent
the user defined signal 2
.Pq Dv USR2 .
.Pp
When shutting down the machine,
.Nm
will try to run the
.Pa /etc/rc.shutdown
script.
This script can be used to cleanly terminate specific programs such
as
.Nm innd
(the InterNetNews server).
If this script does not terminate within 120 seconds,
.Nm
will terminate it. The timeout can be configured via the
.Xr sysctl 8
variable
.Va kern.init_shutdown_timeout .
.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)" .
.Pp
If run as a user process as shown in the second synopsis line,
.Nm
will emulate
.At V
behavior, i.e. super-user can specify the desired
.Em run-level
on a command line, and
.Nm
will signal the original
(PID 1)
.Nm
as follows:
.Bl -column Run-level SIGTERM
.It Sy "Run-level	Signal	Action"
.It Cm 0 Ta Dv SIGUSR2 Ta "Halt and turn the power off"
.It Cm 1 Ta Dv SIGTERM Ta "Go to single-user mode"
.It Cm 6 Ta Dv SIGINT Ta "Reboot the machine"
.It Cm c Ta Dv SIGTSTP Ta "Block further logins"
.It Cm q Ta Dv SIGHUP Ta Rescan the
.Xr ttys 5
file
.El
.Sh FILES
.Bl -tag -width /etc/rc.shutdown -compact
.It Pa /dev/console
system console device
.It Pa /dev/tty*
terminal ports found in
.Xr ttys 5
.It Pa /var/run/utmpx
record of current users on the system
.It Pa /var/log/wtmpx
record of all logins and logouts
.It Pa /etc/ttys
the terminal initialization information file
.It Pa /etc/rc
system startup commands
.It Pa /etc/rc.shutdown
system shutdown commands
.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.
.Bf -emphasis
Init will sleep for 30 seconds,
then continue trying to start the process.
.Ef
.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 dummynet 4 ,
.Xr ipfirewall 4 ,
.Xr kld 4 ,
.Xr ttys 5 ,
.Xr crash 8 ,
.Xr getty 8 ,
.Xr halt 8 ,
.Xr ipfw 8 ,
.Xr rc 8 ,
.Xr reboot 8 ,
.Xr shutdown 8 ,
.Xr sysctl 8
.Sh HISTORY
An
.Nm
utility appeared in
.At v1 .
.Sh CAVEATS
Systems without
.Xr sysctl 8
behave as though they have security level \-1.
.Pp
Setting the security level above 1 too early in the boot sequence can
prevent
.Xr fsck 8
from repairing inconsistent file systems.  The
preferred location to set the security level is at the end of
.Pa /etc/rc
after all multi-user startup actions are complete.