IRIX Operating Levels

IRIX Operating Levels

The IRIX system can run in either single-user or multiuser mode. In single-user mode, only a few processes are active on the system, no graphics are available, and only a single login is allowed. In multiuser mode, there can be multiple login sessions, many files open at once, and many active processes, including numerous background daemons.

The init program controls whether the system is in the multiuser or single-user state. Each possible state that the system can be in is assigned a label, either a number or a letter. The shutdown state is state 0. Single-user mode is state s.

Multiuser state labeling is more complex, because there can be great variations in multiuser states. For example, in one multiuser state, there can be unlimited logins, but in another state there can be a restricted number of logins. The different states can all be assigned different numbers.

The state of the system is controlled by the file /etc/inittab. This file lists the possible states, and the label associated with each.

When you bring the system to standard multiuser mode, init state 2, the following happen:

The file systems are mounted.
The cron daemon is started for scheduled tasks.
Network services are started, if turned on.
The serial-line networking functions of uucp are available for use.
The spooling and scheduling functions of the lp package (if added to the system) are available for use.
Users can log in.

Not all activities can or should be performed in the multiuser state. Some tasks, such as installing software that requires the miniroot and checking file systems must be done with the system in single-user mode.

There are many synonyms for the system state. These include:

init state
run state
run level
run mode
system state

Likewise, each system state may be referred to in a number of ways; for example:

single user
single-user mode
run level 1

Table 3-1 shows the various possible states of the operating system as it is shipped. You can, of course, create your own custom states.

System States
Run Level Description
0 Power-down state.
1, s, or S Single-user mode is used to install/remove software utilities, run file system backups/restores, and check file systems. This state unmounts everything except root, and kills all user processes except those that relate to the console.
2 Multiuser mode is the normal operating mode for the system. The default is that the root (/) and user (/usr) file systems are mounted in this mode. When the system is powered up, it is put in multiuser mode.
6 Reboot mode is used to bring down the system and then bring it back up again. This mode is useful when you are changing certain system configuration parameters.

System States
Run Level	Description
0	Power-down state.
1, s, or S	Single-user mode is used to install/remove software utilities, run file system backups/restores, and check file systems. This state unmounts everything except root, and kills all user processes except those that relate to the console.
2	Multiuser mode is the normal operating mode for the system. The default is that the root (/) and user (/usr) file systems are mounted in this mode. When the system is powered up, it is put in multiuser mode.
6	Reboot mode is used to bring down the system and then bring it back up again. This mode is useful when you are changing certain system configuration parameters.

How init Controls the System State
Entering the Multiuser State from System Shutdown