396 lines
11 KiB
Groff
396 lines
11 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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.\" $FreeBSD$
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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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.Nm init
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.Oo
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.Cm 0 | 1 | 6 |
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.Cm c | q
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.Oc
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.Sh DESCRIPTION
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The
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.Nm
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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 rc 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
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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
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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
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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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.Em console
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entry in the
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.Xr ttys 5
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file is marked
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.Dq insecure ,
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then
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.Nm
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will require that the super-user 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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.Em console
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is marked as
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.Dq secure .
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.Pp
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The kernel runs with four different levels of security.
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Any super-user process can raise the security level, but no process
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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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This is the default initial value.
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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 \- the system immutable and system append-only flags may not
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be turned off;
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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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.Pp
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In addition, kernel time changes are restricted to less than or equal to one
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second. Attempts to change the time by more than this will log the message
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.Dq Time adjustment clamped to +1 second .
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.It Ic 3
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Network secure mode \- same as highly secure mode, plus
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IP packet filter rules (see
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.Xr ipfw 8
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and
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.Xr ipfirewall 4 )
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cannot be changed and
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.Xr dummynet 4
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configuration cannot be adjusted.
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.El
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.Pp
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If the security level is initially nonzero, then
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.Nm
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leaves it unchanged.
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Otherwise,
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.Nm
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raises the level to 1 before going multi-user for the first time.
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Since the level can not be reduced, it will be at least 1 for
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subsequent operation, even on return to single-user.
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If a level higher than 1 is desired while running multi-user,
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it can be set before going multi-user, e.g., by the startup script
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.Xr rc 8 ,
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using
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.Xr sysctl 8
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to set the
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.Dq kern.securelevel
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variable to the required security level.
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.Pp
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In multi-user operation,
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.Nm
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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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unless the first field refers to a device in
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.Pa /dev
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which is not configured.
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The first field is supplied as the final argument to the command.
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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
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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
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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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.Nm Init
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can also be used to keep arbitrary daemons running,
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automatically restarting them if they die.
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In this case, the first field in the
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.Xr ttys 5
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file must not reference the path to a configured device node
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and will be passed to the daemon
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as the final argument on its command line.
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This is similar to the facility offered in the
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.At V
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.Pa /etc/inittab .
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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
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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
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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
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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
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executes the command specified in the second field.
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If the command 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
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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
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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
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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 processes
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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 machine appears to be hung.
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.Pp
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.Nm Init
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will do the same, except it will halt the machine if sent
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the user defined signal 1
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.Pq Dv USR1 ,
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or will halt and turn the power off (if hardware permits) if sent
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the user defined signal 2
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.Pq Dv USR2 .
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.Pp
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When shutting down the machine,
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.Nm
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will try to run the
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.Pa /etc/rc.shutdown
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script.
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This script can be used to cleanly terminate specific programs such
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as
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.Nm innd
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(the InterNetNews server).
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.Pp
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The role of
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.Nm
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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
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process cannot be located, the system will panic with the message
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.Dq "panic: init died (signal %d, exit %d)" .
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.Pp
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If run as a user process as shown in the second synopsis line,
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.Nm
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will emulate
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.At V
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behavior, i.e. super-user can specify the desired
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.Em run-level
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on a command line, and
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.Nm
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will signal the original
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.Pq PID 1
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.Nm
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as follows:
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.Bl -column Run-level SIGTERM
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.It Sy Run-level Signal Action
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.It Cm 0 Ta Dv SIGUSR2 Ta "Halt and turn the power off"
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.It Cm 1 Ta Dv SIGTERM Ta "Go to single-user mode"
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.It Cm 6 Ta Dv SIGINT Ta "Reboot the machine"
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.It Cm c Ta Dv SIGTSTP Ta "Block further logins"
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.It Cm q Ta Dv SIGHUP Ta Rescan the
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.Xr ttys 5
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file
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.El
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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 30 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 /etc/rc.shutdown -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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.It Pa /etc/rc.shutdown
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system shutdown commands
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.El
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.Sh SEE ALSO
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.Xr kill 1 ,
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.Xr login 1 ,
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.Xr sh 1 ,
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.Xr dummynet 4 ,
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.Xr ipfirewall 4 ,
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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 halt 8 ,
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.Xr ipfw 8 ,
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.Xr rc 8 ,
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.Xr reboot 8 ,
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.Xr shutdown 8 ,
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.Xr sysctl 8
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.Sh HISTORY
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An
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.Nm
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command appeared in
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.At v6 .
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.Sh CAVEATS
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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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.Pp
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Setting the security level above 1 too early in the boot sequence can
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prevent
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.Xr fsck 8
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from repairing inconsistent filesystems. The
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preferred location to set the security level is at the end of
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.Pa /etc/rc
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after all multi-user startup actions are complete.
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