.\" 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 8.6 (Berkeley) 5/26/95 .\" .Dd May 26, 1995 .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. The .Xr settimeofday 2 system call can only advance the time. .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/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. .pl +1 .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.