Note: The information contained in this article is structured as help information for the System Management Interface Tool (SMIT) and is not intended for use as a procedural or conceptual article.
A run level can be viewed as a software configuration of the system that allows only a selected group of processes to exist. The system can be in one of eleven run levels, 0 through 9, or S, s, M, or m (S, s, M, and m are identical). When the system level is changed, the init command cancels all processes that it tracks that should not be running at the new level and starts any processes listed in the /etc/inittab file that should be running at the new level.
A run level can be viewed as a software configuration of the system that allows only a selected group of processes to exist. The system can be in one of eleven run levels, 0 through 9, or S, s, M, or m (S, s, M, and m are identical). When the system level is changed, the init command cancels all processes that it tracks that should not be running at the new level and starts any processes listed in the /etc/inittab file that should be running at the new level.
Tells the init command to enter the maintenance mode.
During the default shutdown, users are notified (by a wall command) of the impending system shutdown with a message.
Interactive messages are displayed to guide the user through the shutdown.
The system is restarted after being shutdown.
The Time parameter is the time at which the shutdown command stops the system. An immediate shutdown is indicated by the word now displayed on the screen. A future time can be specified in one of two formats: +number or hour:minute. The first form brings the system down in the specified number of minutes and the second brings the system down at the time of day indicated (as a 24-hour clock).
When the init command is requested to change run levels by the telinit command, the init command sends a SIGTERM signal to all processes that are undefined in the current run level. The init command will wait twenty seconds before stopping these processes with the SIGKILL signal.
If the init command receives a SIGPWR signal and is not in maintenance mode, it scans the inittab file for special powerfail entries. These entries are invoked (if the run levels permit) before any further processing takes place. In this way the init command can perform cleanup and recording functions whenever the system experiences a power failure. It is important to note that these power fail entries should not use devices that need to be initialized first.
The telinit command, which is linked to the init command, is used to direct the actions of the init command. It takes a one character argument and signals the init command by way of the kill subroutine to perform the appropriate action. The following arguments serve as directives to the init command:
0-9 - Tells the init command to place the system in one of the run levels 0-9.
a,b,c - Tells the init command to process only those inittab file entries having the a, b, or c run level set.
Q,q - Tells the init command to re-examine the inittab file.
Specifies the kernel used to boot the system when a network boot occurs. The following values are valid:
up - Use the kernel for single processor machines.
mp - Use the kernel for multiprocessor machines.