If the console entry in the ttys(5) file is marked ``insecure'' then will require that the super-user password be entered before the system will start a single-user shell. The password check is skipped if the console is marked as ``secure''
If the system security level (see security(7)) is initially nonzero, then leaves it unchanged. Otherwise, raises the level to 1 before going multi-user for the first time. Since the level cannot be reduced, it will be at least 1 for subsequent operation, even on return to single-user. If a level higher than 1 is desired while running multi-user, it can be set before going multi-user, e.g., by the startup script rc(8), using sysctl(8) to set the kern.securelevel variable to the required security level.
If is run in a jail, the security level of the ``host system'' will not be affected. Part of the information set up in the kernel to support a jail is a per-jail security level. 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, maintains processes for the terminal ports found in the file ttys(5). The 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) program. 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 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 executing a new getty for the line.
The 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 command line. This is similar to the facility offered in the AT&T System V /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 with the command ``kill -HUP 1 '' On receipt of this signal, re-reads the ttys(5) file. When a line is turned off in ttys(5), 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, 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 starts a process on the line). If a line is commented out or deleted from ttys(5), 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 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), 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 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 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 shutting the machine down cleanly from inside the kernel or from X when the machine appears to be hung.
The utility will do the same, except it will halt the machine if sent the user defined signal 1 (USR1 ) or will halt and turn the power off (if hardware permits) if sent the user defined signal 2 (USR2 )
When shutting down the machine, will try to run the /etc/rc.shutdown script. This script can be used to cleanly terminate specific programs such as innd (the InterNetNews server). If this script does not terminate within 120 seconds, will terminate it. The timeout can be configured via the sysctl(8) variable kern.init_shutdown_timeout
The role of is so critical that if it dies, the system will reboot itself automatically. If, at bootstrap time, the 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, will emulate AT&T System V behavior, i.e., super-user can specify the desired run-level on a command line, and will signal the original (PID 1) as follows:
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.