38058917d5
match reality. Say that secured devices `may not be opened for writing' instead of `are read-only'.
302 lines
8.4 KiB
Groff
302 lines
8.4 KiB
Groff
.\" Copyright (c) 1980, 1991, 1993
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.\" The Regents of the University of California. All rights reserved.
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.\"
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.\" This code is derived from software contributed to Berkeley by
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.\" Donn Seeley at Berkeley Software Design, Inc.
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.\"
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.\" Redistribution and use in source and binary forms, with or without
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.\" modification, are permitted provided that the following conditions
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.\" are met:
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.\" 1. Redistributions of source code must retain the above copyright
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.\" notice, this list of conditions and the following disclaimer.
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.\" 2. Redistributions in binary form must reproduce the above copyright
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.\" notice, this list of conditions and the following disclaimer in the
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.\" documentation and/or other materials provided with the distribution.
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.\" 3. All advertising materials mentioning features or use of this software
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.\" must display the following acknowledgement:
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.\" This product includes software developed by the University of
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.\" California, Berkeley and its contributors.
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.\" 4. Neither the name of the University nor the names of its contributors
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.\" may be used to endorse or promote products derived from this software
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.\" without specific prior written permission.
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.\"
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.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
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.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
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.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
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.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
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.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
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.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
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.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
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.\" SUCH DAMAGE.
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.\"
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.\" @(#)init.8 8.3 (Berkeley) 4/18/94
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.\"
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.Dd April 18, 1994
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.Dt INIT 8
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.Os BSD 4
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.Sh NAME
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.Nm init
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.Nd process control initialization
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.Sh SYNOPSIS
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.Nm init
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.Sh DESCRIPTION
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The
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.Nm init
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program
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is the last stage of the boot process.
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It normally runs the automatic reboot sequence as described in
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.Xr reboot 8 ,
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and if this succeeds, begins multi-user operation.
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If the reboot scripts fail,
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.Nm init
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commences single user operation by giving
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the super-user a shell on the console.
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The
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.Nm init
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program may be passed parameters
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from the boot program to
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prevent the system from going multi-user and to instead execute
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a single user shell without starting the normal daemons.
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The system is then quiescent for maintenance work and may
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later be made to go to multi-user by exiting the
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single-user shell (with ^D).
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This
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causes
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.Nm init
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to run the
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.Pa /etc/rc
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start up command file in fastboot mode (skipping disk checks).
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.Pp
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If the
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.Nm console
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entry in the
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.Xr ttys 5
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file is marked ``insecure'',
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then
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.Nm init
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will require that the superuser password be
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entered before the system will start a single-user shell.
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The password check is skipped if the
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.Nm console
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is marked as ``secure''.
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.Pp
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The kernel runs with four different levels of security.
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Any superuser process can raise the security level, but only
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.Nm init
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can lower it.
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The security levels are:
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.Bl -tag -width flag
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.It Ic -1
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Permanently insecure mode \- always run the system in level 0 mode.
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.It Ic 0
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Insecure mode \- immutable and append-only flags may be turned off.
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All devices may be read or written subject to their permissions.
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.It Ic 1
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Secure mode \- immutable and append-only flags may not be changed;
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disks for mounted filesystems,
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.Pa /dev/mem ,
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and
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.Pa /dev/kmem
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may not be opened for writing.
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.It Ic 2
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Highly secure mode \- same as secure mode, plus disks may not be
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opened for writing (except by
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.Xr mount 2 )
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whether mounted or not.
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This level precludes tampering with filesystems by unmounting them,
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but also inhibits running
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.Xr newfs 8
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while the system is multi-user.
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.El
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.Pp
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If the security level is initially -1, then
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.Nm init
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leaves it unchanged.
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Otherwise,
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.Nm init
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arranges to run the system in level 0 mode while single user
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and in level 1 mode while multiuser.
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If level 2 mode is desired while running multiuser,
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it can be set while single user, e.g., in the startup script
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.Pa /etc/rc ,
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using
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.Xr sysctl 8 .
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.Pp
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In multi-user operation,
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.Nm init
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maintains
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processes for the terminal ports found in the file
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.Xr ttys 5 .
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.Nm Init
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reads this file, and executes the command found in the second field.
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This command is usually
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.Xr getty 8 ;
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.Nm getty
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opens and initializes the tty line
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and
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executes the
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.Xr login 1
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program.
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The
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.Nm login
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program, when a valid user logs in,
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executes a shell for that user. When this shell
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dies, either because the user logged out
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or an abnormal termination occurred (a signal),
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the
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.Nm init
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program wakes up, deletes the user
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from the
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.Xr utmp 5
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file of current users and records the logout in the
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.Xr wtmp 5
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file.
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The cycle is
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then restarted by
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.Nm init
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executing a new
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.Nm getty
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for the line.
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.Pp
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Line status (on, off, secure, getty, or window information)
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may be changed in the
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.Xr ttys 5
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file without a reboot by sending the signal
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.Dv SIGHUP
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to
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.Nm init
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with the command
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.Dq Li "kill -HUP 1" .
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On receipt of this signal,
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.Nm init
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re-reads the
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.Xr ttys 5
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file.
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When a line is turned off in
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.Xr ttys 5 ,
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.Nm init
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will send a SIGHUP signal to the controlling process
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for the session associated with the line.
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For any lines that were previously turned off in the
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.Xr ttys 5
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file and are now on,
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.Nm init
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executes a new
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.Nm getty
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to enable a new login.
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If the getty or window field for a line is changed,
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the change takes effect at the end of the current
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login session (e.g., the next time
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.Nm init
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starts a process on the line).
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If a line is commented out or deleted from
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.Xr ttys 5 ,
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.Nm init
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will not do anything at all to that line.
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However, it will complain that the relationship between lines
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in the
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.Xr ttys 5
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file and records in the
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.Xr utmp 5
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file is out of sync,
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so this practice is not recommended.
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.Pp
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.Nm Init
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will terminate multi-user operations and resume single-user mode
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if sent a terminate
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.Pq Dv TERM
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signal, for example,
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.Dq Li "kill \-TERM 1" .
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If there are processes outstanding that are deadlocked (because of
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hardware or software failure),
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.Nm init
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will not wait for them all to die (which might take forever), but
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will time out after 30 seconds and print a warning message.
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.Pp
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.Nm Init
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will cease creating new
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.Nm getty Ns 's
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and allow the system to slowly die away, if it is sent a terminal stop
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.Pq Dv TSTP
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signal, i.e.
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.Dq Li "kill \-TSTP 1" .
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A later hangup will resume full
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multi-user operations, or a terminate will start a single user shell.
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This hook is used by
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.Xr reboot 8
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and
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.Xr halt 8 .
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.Pp
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.Nm Init
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will terminate all possible processes (again, it will not wait
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for deadlocked processes) and reboot the machine if sent the interrupt
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.Pq Dv INT
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signal, i.e.
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.Dq Li "kill \-INT 1".
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This is useful for shutting the machine down cleanly from inside the kernel
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or from X when the machines appears to be hung.
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.Pp
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The role of
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.Nm init
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is so critical that if it dies, the system will reboot itself
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automatically.
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If, at bootstrap time, the
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.Nm init
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process cannot be located, the system will panic with the message
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``panic: "init died (signal %d, exit %d)''.
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.Sh DIAGNOSTICS
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.Bl -diag
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.It "getty repeating too quickly on port %s, sleeping"
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A process being started to service a line is exiting quickly
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each time it is started.
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This is often caused by a ringing or noisy terminal line.
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.Em "Init will sleep for 10 seconds" ,
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.Em "then continue trying to start the process" .
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.Pp
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.It "some processes would not die; ps axl advised."
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A process
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is hung and could not be killed when the system was shutting down.
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This condition is usually caused by a process
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that is stuck in a device driver because of
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a persistent device error condition.
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.El
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.Sh FILES
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.Bl -tag -width /var/log/wtmp -compact
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.It Pa /dev/console
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System console device.
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.It Pa /dev/tty*
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Terminal ports found in
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.Xr ttys 5 .
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.It Pa /var/run/utmp
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Record of Current users on the system.
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.It Pa /var/log/wtmp
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Record of all logins and logouts.
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.It Pa /etc/ttys
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The terminal initialization information file.
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.It Pa /etc/rc
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System startup commands.
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.El
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.Sh SEE ALSO
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.Xr login 1 ,
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.Xr kill 1 ,
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.Xr sh 1 ,
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.Xr ttys 5 ,
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.Xr crash 8 ,
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.Xr getty 8 ,
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.Xr rc 8 ,
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.Xr reboot 8 ,
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.Xr halt 8 ,
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.Xr shutdown 8
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.Sh HISTORY
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A
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.Nm
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command appeared in
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.At v6 .
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.Sh BUGS
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Systems without
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.Xr sysctl
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behave as though they have security level \-1.
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