When you boot the system or change run levels with the init or shutdown command, the init daemon starts processes by reading information from the /etc/inittab file. This file defines three important items for the init process:
The system's default run level
What processes to start, monitor, and restart if they terminate
What actions to be taken when the system enters a new run level
Each entry in the /etc/inittab file has the following fields:
id:rstate:action:process
Table 6-2 describes the fields in an inittab entry.
Table 6-2 Fields in the inittab File
Field |
Description |
---|---|
id |
A unique identifier for the entry |
rstate |
The run level, which corresponds to the command or (script) to be processed |
action |
How the process specified in the process field is to be run |
process |
The name of the process (or command) to execute |
The following example shows an annotated default inittab file:
The init process is started and reads the /etc/default/init file to set any environment variables. By default, only the TIMEZONE variable is set.
Then init reads the inittab file to do the following:
Identify the initdefault entry, which defines the default run level (3).
Execute any process entries that have sysinit in the action field so that any special initializations can take place before users login.
Execute any process entries that have 3 in the rstate field, which matches the default run level, 3.
See init(1M) for a detailed description of how the init process uses the inittab file.
Table 6-3 describes the key words used for run level 3's action field.
Table 6-3 Run Level 3 Action Key Word Descriptions
Key Word |
Starts the Specified Process ... |
---|---|
powerfail |
Only when the system receives a power fail signal. |
wait |
And waits for its termination. |
respawn |
If it does not exist. If the process already exists, continue scanning the inittab file. |
Table 6-4 describes the processes (or commands) executed at run level 3.
Table 6-4 Run Level 3 Command Descriptions
Command or Script Name |
Description |
---|---|
/usr/sbin/shutdown |
Shuts down the system. The init process runs the shutdown command only if the system has received a powerfail signal. |
/sbin/rc2 |
Sets up the time zone, then starts the standard system processes, bringing the system up into run level 2 (multiuser mode). |
/sbin/rc3 |
Starts NFS resource sharing for run level 3. |
/usr/lib/saf/sac -t 30 |
Starts the port monitors and network access for UUCP. This process is restarted if it fails. |
/usr/lib/saf/ttymon -g -h -p "`uname -n` console login: " -T terminal_type -d /dev/console -l console |
Starts the ttymon process that monitors the console for login requests. This process is restarted if it fails. The terminal_type on a SPARC system is sun The terminal_type on a x86 system is AT386 |