NetBSD/sbin/init/init.8

.\"	$NetBSD: init.8,v 1.60 2016/09/11 22:22:57 sevan Exp $
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.\" Donn Seeley at Berkeley Software Design, Inc.
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.\"     @(#)init.8	8.6 (Berkeley) 5/26/95
.\"
.Dd September 11, 2016
.Dt INIT 8
.Os
.Sh NAME
.Nm init
.Nd process control initialization
.Sh SYNOPSIS
.Nm
.Op Fl s
.Sh DESCRIPTION
The
.Nm
program is the last stage of the boot process.
It normally begins multi-user operation.
.Pp
.Nm
is executed automatically by the kernel,
after the kernel has initialised all devices
and mounted the root file system.
The kernel may try multiple possible paths for
.Nm ,
including
.Pa /sbin/init ,
.Pa /sbin/oinit ,
.Pa /sbin/init.bak ,
and
.Pa /rescue/init .
.Pp
The following table describes the state machine used by
.Nm :
.Bl -enum
.It
Single user shell.
If the kernel is booted in single user mode (see
.Xr boothowto 9 ) ,
then the kernel will pass the
.Fl s
option to
.Nm
to prevent the system from going multi-user and
to instead execute a single user shell without starting the normal
daemons.
If the kernel is in a secure mode,
.Nm
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).
.It
Multi-user boot (default operation).
Executes
.Pa /etc/rc
(see
.Xr rc 8 ) .
If this was the first state entered (as opposed to entering here after
state 1), then
.Pa /etc/rc
will be invoked with its first argument being
.Sq autoboot .
If
.Pa /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.
.Pp
If value of the
.Dq init.root
sysctl node is not equal to
.Pa /
at this point, the
.Pa /etc/rc
process will be run inside a
.Xr chroot 2
indicated by sysctl with the same error handling as above.
.Pp
If the administrator has not set the security level to \-1
to indicate that the kernel should not run multiuser in secure
mode, and the
.Pa /etc/rc
script has not set a higher level of security
than level 1, then
.Nm
will put the kernel into securelevel mode 1.
See
.Xr rc.conf 5
and
.Xr secmodel_securelevel 9
for more information.
.It
Set up ttys as specified in
.Xr ttys 5 .
See below for more information.
On completion, continue to state 4.
If we did chroot in state 2, each
.Xr getty 8
process will be run in the same
.Xr chroot 2
path as in 2 (that is, the value of
.Dq init.root
sysctl is not re-read).
.It
Multi-user operation.
Depending upon the signal received, change state appropriately;
on
.Dv SIGTERM ,
go to state 7;
on
.Dv SIGHUP ,
go to state 5;
on
.Dv SIGTSTP ,
go to state 6.
.It
Clean-up mode; re-read
.Xr ttys 5 ,
killing off the controlling processes on lines that are now
.Sq off ,
and starting processes that are newly
.Sq on .
On completion, go to state 4.
.It
.Sq Boring
mode; no new sessions.
Signals as per state 4.
.It
Shutdown mode.
Send
.Dv 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.
.El
.Pp
If the
.Sq console
entry in the
.Xr ttys 5
file is marked
.Dq insecure ,
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
.Sq console
is marked as
.Dq secure .
.Pp
It should be noted that while
.Nm
has the ability to start multi-user operation inside a
.Xr chroot 2
environment, the
.Nm
process itself will always run in the
.Dq original root directory .
This also implies that single-user mode is always started in the original
root, giving the possibility to create multi-user sessions in different
root directories over time.
The
.Dq init.root
sysctl node is fabricated by
.Nm
at startup and re-created any time it is 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 specification).
.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 ;
it opens and initializes the tty line and executes the
.Xr login 1
program.
The
.Xr 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
.Nm
program wakes up, deletes the user from the
.Xr utmp 5
and
.Xr utmpx 5
files of current users and records the logout in the
.Xr wtmp 5
and
.Xr wtmpx 5
files.
The cycle is
then restarted by
.Nm
executing a new
.Xr getty 8
for the line.
.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 \-s HUP 1" .
This is referenced in the table above as state 5.
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 a new
.Xr 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
.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 utmp 5
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 \-s 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 8 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 \-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
.Xr reboot 8
and
.Xr halt 8 .
.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, or exits during its initialisation,
the system will panic with the message
.Dq panic: init died (signal %d, exit %d) .
.Pp
If
.Pa /dev/console
does not exist,
.Nm
will cd to
.Pa /dev
and run
.Dq Li "MAKEDEV -MM init" .
.Xr MAKEDEV 8
will use
.Xr mount_tmpfs 8
or
.Xr mount_mfs 8
to create a memory file system mounted over
.Pa /dev
that contains the standard devices considered necessary to boot the system.
.Sh FILES
.Bl -tag -width /var/log/wtmp{,x} -compact
.It Pa /dev/console
System console device.
.It Pa /dev/tty*
Terminal ports found in
.Xr ttys 5 .
.It Pa /var/run/utmp{,x}
Record of current users on the system.
.It Pa /var/log/wtmp{,x}
Record of all logins and logouts.
.It Pa /etc/ttys
The terminal initialization information file.
.It Pa /etc/rc
System startup 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.
.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 config 1 ,
.Xr kill 1 ,
.Xr login 1 ,
.Xr sh 1 ,
.Xr options 4 ,
.Xr ttys 5 ,
.Xr getty 8 ,
.Xr halt 8 ,
.Xr MAKEDEV 8 ,
.Xr MAKEDEV.local 8 ,
.Xr mount_mfs 8 ,
.Xr mount_tmpfs 8 ,
.Xr rc 8 ,
.Xr reboot 8 ,
.Xr rescue 8 ,
.Xr shutdown 8 ,
.Xr sysctl 8 ,
.Xr secmodel_bsd44 9 ,
.Xr secmodel_securelevel 9
.Sh HISTORY
A
.Nm
command appeared in
.At v1 .