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securelevel(8)

NAME

     init -- process control initialization

SYNOPSIS

     init
     init [0 | 1 | 6 | c | q]

DESCRIPTION

     The init utility is the last stage of the boot process.  It normally runs
     the automatic reboot sequence as described in rc(8), and if this suc-
     ceeds, begins multi-user operation.  If the reboot scripts fail, init
     commences single-user operation by giving the super-user a shell on the
     console.  The init utility may be passed parameters from the boot program
     to prevent the system from going multi-user and to instead execute a sin-
     gle-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 init to run the
     /etc/rc start up command file in fastboot mode (skipping disk checks).

     If the console entry in the ttys(5) file is marked ``insecure'', then
     init will require that the super-user password be entered before the sys-
     tem will start a single-user shell.  The password check is skipped if the
     console is marked as ``secure''.

     The kernel runs with five different levels of security.  Any super-user
     process can raise the security level, but no process can lower it.  The
     security levels are:

     -1    Permanently insecure mode - always run the system in level 0 mode.
	   This is the default initial value.

     0	   Insecure mode - immutable and append-only flags may be turned off.
	   All devices may be read or written subject to their permissions.

     1	   Secure mode - the system immutable and system append-only flags may
	   not be turned off; disks for mounted file systems, /dev/mem,
	   /dev/kmem and /dev/io (if your platform has it) may not be opened
	   for writing; kernel modules (see kld(4)) may not be loaded or
	   unloaded.

     2	   Highly secure mode - same as secure mode, plus disks may not be
	   opened for writing (except by mount(2)) whether mounted or not.
	   This level precludes tampering with file systems by unmounting
	   them, but also inhibits running newfs(8) while the system is multi-
	   user.

	   In addition, kernel time changes are restricted to less than or
	   equal to one second.  Attempts to change the time by more than this
	   will log the message ``Time adjustment clamped to +1 second''.

     3	   Network secure mode - same as highly secure mode, plus IP packet
	   filter rules (see ipfw(8), ipfirewall(4) and pfctl(8)) cannot be
	   changed and dummynet(4) or pf(4) configuration cannot be adjusted.

     If the security level is initially nonzero, then init leaves it
     unchanged.  Otherwise, init raises the level to 1 before going multi-user
     for the first time.  Since the level cannot be reduced, it will be at
     a jail is a per-jail ``securelevel'' setting.  This allows running a
     higher security level inside of a jail than that of the host system.  See
     jail(8) for more information about jails.

     In multi-user operation, init maintains processes for the terminal ports
     found in the file ttys(5).  The init utility reads this file and executes
     the command found in the second field, unless the first field refers to a
     device in /dev which is not configured.  The first field is supplied as
     the final argument to the command.  This command is usually getty(8);
     getty opens and initializes the tty line and executes the login(1) pro-
     gram.  The 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 init utility wakes up,
     deletes the user from the utmp(5) file of current users and records the
     logout in the wtmp(5) file.  The cycle is then restarted by init execut-
     ing a new getty for the line.

     The init utility can also be used to keep arbitrary daemons running,
     automatically restarting them if they die.  In this case, the first field
     in the ttys(5) file must not reference the path to a configured device
     node and will be passed to the daemon as the final argument on its com-
     mand line.  This is similar to the facility offered in the AT&T System V
     UNIX /etc/inittab.

     Line status (on, off, secure, getty, or window information) may be
     changed in the ttys(5) file without a reboot by sending the signal SIGHUP
     to init with the command ``kill -HUP 1''.	On receipt of this signal,
     init re-reads the ttys(5) file.  When a line is turned off in ttys(5),
     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 ttys(5) file and are now on, init executes the command specified
     in the second field.  If the command 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 init starts a process on the line).  If a line is
     commented out or deleted from ttys(5), init will not do anything at all
     to that line.  However, it will complain that the relationship between
     lines in the ttys(5) file and records in the utmp(5) file is out of sync,
     so this practice is not recommended.

     The init utility will terminate multi-user operations and resume single-
     user mode if sent a terminate (TERM) signal, for example, ``kill -TERM
     1''.  If there are processes outstanding that are deadlocked (because of
     hardware or software failure), 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.

     The init utility will cease creating new processes and allow the system
     to slowly die away, if it is sent a terminal stop (TSTP) signal, i.e.
     ``kill -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
     reboot(8) and halt(8).

     The init utility will terminate all possible processes (again, it will
     not wait for deadlocked processes) and reboot the machine if sent the
     interrupt (INT) signal, i.e. ``kill -INT 1''.  This is useful for shut-
     ting the machine down cleanly from inside the kernel or from X when the
     machine appears to be hung.

     The role of init is so critical that if it dies, the system will reboot
     itself automatically.  If, at bootstrap time, the init process cannot be
     located, the system will panic with the message ``panic: init died
     (signal %d, exit %d)''.

     If run as a user process as shown in the second synopsis line, init will
     emulate AT&T System V UNIX behavior, i.e., super-user can specify the
     desired run-level on a command line, and init will signal the original
     (PID 1) init as follows:

     Run-level	  Signal     Action
     0		  SIGUSR2    Halt and turn the power off
     1		  SIGTERM    Go to single-user mode
     6		  SIGINT     Reboot the machine
     c		  SIGTSTP    Block further logins
     q		  SIGHUP     Rescan the ttys(5) file

DIAGNOSTICS

     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.	Init will
     sleep for 30 seconds, then continue trying to start the process.

     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.

FILES

     /dev/console      system console device
     /dev/tty*	       terminal ports found in ttys(5)
     /var/run/utmp     record of current users on the system
     /var/log/wtmp     record of all logins and logouts
     /etc/ttys	       the terminal initialization information file
     /etc/rc	       system startup commands
     /etc/rc.shutdown  system shutdown commands

SEE ALSO

     kill(1), login(1), sh(1), dummynet(4), ipfirewall(4), kld(4), pf(4),
     ttys(5), crash(8), getty(8), halt(8), ipfw(8), jail(8), pfctl(8), rc(8),
     reboot(8), shutdown(8), sysctl(8)

HISTORY

     An init utility appeared in Version 6 AT&T UNIX.

CAVEATS

     Systems without sysctl(8) behave as though they have security level -1.

     Setting the security level above 1 too early in the boot sequence can
     prevent fsck(8) from repairing inconsistent file systems.	The preferred
     location to set the security level is at the end of /etc/rc after all
     multi-user startup actions are complete.

FreeBSD 5.4			April 18, 1994			   FreeBSD 5.4

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