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+.\"	$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.
+.\"
+.\" This code is derived from software contributed to Berkeley by
+.\" Donn Seeley at Berkeley Software Design, Inc.
+.\"
+.\" Redistribution and use in source and binary forms, with or without
+.\" modification, are permitted provided that the following conditions
+.\" are met:
+.\" 1. Redistributions of source code must retain the above copyright
+.\"    notice, this list of conditions and the following disclaimer.
+.\" 2. Redistributions in binary form must reproduce the above copyright
+.\"    notice, this list of conditions and the following disclaimer in the
+.\"    documentation and/or other materials provided with the distribution.
+.\" 3. All advertising materials mentioning features or use of this software
+.\"    must display the following acknowledgement:
+.\"	This product includes software developed by the University of
+.\"	California, Berkeley and its contributors.
+.\" 4. Neither the name of the University nor the names of its contributors
+.\"    may be used to endorse or promote products derived from this software
+.\"    without specific prior written permission.
+.\"
+.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
+.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
+.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+.\" SUCH DAMAGE.
+.\"
+.\"     @(#)init.8	8.3 (Berkeley) 4/18/94
+.\"
+.Dd April 18, 1994
+.Dt INIT 8
+.Os BSD 4
+.Sh NAME
+.Nm init
+.Nd process control initialization
+.Sh SYNOPSIS
+.Nm init
+.Sh DESCRIPTION
+The
+.Nm init
+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 init
+commences single user operation by giving
+the super-user a shell on the console.
+The
+.Nm 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 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 init
+to run the
+.Pa /etc/rc
+start up command file in fastboot mode (skipping disk checks).
+.Pp
+If the
+.Nm console
+entry in the
+.Xr ttys 5
+file is marked ``insecure'',
+then
+.Nm 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 
+.Nm console
+is marked as ``secure''.
+.Pp
+The kernel runs with four different levels of security.
+Any superuser process can raise the security level, but only 
+.Nm init
+can lower it.
+Security levels are defined as follows:
+.Bl -tag -width flag
+.It Ic -1
+Permanently insecure mode \- always run system in level 0 mode.
+.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 \- immutable and append-only flags may not be changed;
+disks for mounted filesystems,
+.Pa /dev/mem ,
+and
+.Pa /dev/kmem
+are read-only.
+.It Ic 2
+Highly secure mode \- same as secure mode, plus disks are always
+read-only whether mounted or not.
+This level precludes tampering with filesystems by unmounting them,
+but also inhibits running
+.Xr newfs 8
+while the system is multi-user.
+.El
+.Pp
+Normally, the system runs in level 0 mode while single user
+and in level 1 mode while multiuser.
+If the level 2 mode is desired while running multiuser,
+it can be set in the startup script
+.Pa /etc/rc
+using
+.Xr sysctl 8 .
+If it is desired to run the system in level 0 mode while multiuser,
+the administrator must build a kernel with the variable
+.Nm securelevel
+defined in the file
+.Pa /sys/arch/compile/MACHINE/param.c
+and initialize it to -1.
+.Pp
+In multi-user operation, 
+.Nm init
+maintains
+processes for the terminal ports found in the file
+.Xr ttys 5 .
+.Nm Init
+reads this file, and executes the command found in the second field.
+This command is usually
+.Xr getty 8 ;
+.Xr getty
+opens and initializes the tty line
+and
+executes the
+.Xr login
+program.
+The
+.Xr 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 init
+program wakes up, deletes the user
+from the
+.Xr utmp 5
+file of current users and records the logout in the
+.Xr wtmp
+file.
+The cycle is
+then restarted by
+.Nm init
+executing a new
+.Xr getty
+for the line.
+.Pp
+Line status (on, off, secure, getty, or window information)
+may be changed in the
+.Xr ttys
+file without a reboot by sending the signal
+.Dv SIGHUP
+to
+.Nm init
+with the command
+.Dq Li "kill \-s HUP 1" .
+On receipt of this signal,
+.Nm init
+re-reads the
+.Xr ttys
+file.
+When a line is turned off in
+.Xr ttys ,
+.Nm 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
+.Xr ttys
+file and are now on,
+.Nm init
+executes a new
+.Xr 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 init
+starts a process on the line).
+If a line is commented out or deleted from
+.Xr ttys ,
+.Nm init
+will not do anything at all to that line.
+However, it will complain that the relationship between lines
+in the
+.Xr ttys
+file and records in the
+.Xr utmp
+file is out of sync,
+so this practice is not recommended.
+.Pp
+.Nm Init
+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),
+.Xr 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.
+.Pp
+.Nm Init
+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 \-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 init
+is so critical that if it dies, the system will reboot itself
+automatically.
+If, at bootstrap time, the
+.Xr init
+process cannot be located, the system will panic with the message
+``panic: "init died (signal %d, exit %d)''.
+.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 FILES
+.Bl -tag -width /var/log/wtmp -compact
+.It Pa /dev/console
+System console device.
+.It Pa /dev/tty*
+Terminal ports found in
+.Xr ttys .
+.It Pa /var/run/utmp
+Record of Current users on the system.
+.It Pa /var/log/wtmp
+Record of all logins and logouts.
+.It Pa /etc/ttys
+The terminal initialization information file.
+.It Pa /etc/rc
+System startup commands.
+.El
+.Sh SEE ALSO
+.Xr login 1 ,
+.Xr kill 1 ,
+.Xr sh 1 ,
+.Xr ttys 5 ,
+.Xr crash 8 ,
+.Xr getty 8 ,
+.Xr rc 8 ,
+.Xr reboot 8 ,
+.Xr halt 8 ,
+.Xr shutdown 8
+.Sh HISTORY
+A
+.Nm
+command appeared in
+.At v6 .
+.Sh BUGS
+Systems without
+.Xr sysctl
+behave as though they have security level \-1.