The /etc/inittab File

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

The following table describes the fields in an inittab entry.

Example--Default inittab File

The following example shows an annotated default inittab file:

1 ap::sysinit:/sbin/autopush -f /etc/iu.ap
2 ap::sysinit:/sbin/soconfig -f /etc/sock2path
3 fs::sysinit:/sbin/rcS sysinit   >/dev/msglog 2<>/dev/msglog </dev/console
4 is:3:initdefault:
5 p3:s1234:powerfail:/usr/sbin/shutdown -y -i5 -g0 >/dev/msglog 2<>/dev/...
6 sS:s:wait:/sbin/rcS              >/dev/msglog 2<>/dev/msglog </dev/console
7 s0:0:wait:/sbin/rc0              >/dev/msglog 2<>/dev/msglog </dev/console
8 s1:1:respawn:/sbin/rc1           >/dev/msglog 2<>/dev/msglog </dev/console
9 s2:23:wait:/sbin/rc2             >/dev/msglog 2<>/dev/msglog </dev/console
10 s3:3:wait:/sbin/rc3             >/dev/msglog 2<>/dev/msglog </dev/console
11 s5:5:wait:/sbin/rc5             >/dev/msglog 2<>/dev/msglog </dev/console
12 s6:6:wait:/sbin/rc6             >/dev/msglog 2<>/dev/msglog </dev/console
13 fw:0:wait:/sbin/uadmin 2 0      >/dev/msglog 2<>/dev/msglog </dev/console
14 of:5:wait:/sbin/uadmin 2 6      >/dev/msglog 2<>/dev/msglog </dev/console
15 rb:6:wait:/sbin/uadmin 2 1      >/dev/msglog 2<>/dev/msglog </dev/console
16 sc:234:respawn:/usr/lib/saf/sac -t 300
17 co:234:respawn:/usr/lib/saf/ttymon -g -h -p "`uname -n` console login: " 
   -T terminal-type -d /dev/console -l console -m ldterm,ttcompat  

1. Initializes STREAMS modules

2. Configures socket transport providers

3. Initializes file systems

4. Defines default run level

5. Describes a power fail shutdown

6. Defines single-user mode

7. Defines run level 0

8. Defines run level 1

9. Defines run level 2

10. Defines run level 3

11. Defines run level 5

12. Defines run level 6

13. Defines an unused level, firmware

14. Defines an unused level, off

15. Defines an unused level, reboot

16. Initializes Service Access Controller

17. Initializes console

What Happens When the System Is Brought to Run Level 3

1. 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.

2. Then init reads the inittab file to do the following:

   1. Identify the initdefault entry, which defines the default run level (3).

   2. Execute any process entries that have sysinit in the action field so that any special initializations can take place before users login.

   3. 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.

      The following table describes the key words used for run level 3's action field.

      Table 8-3 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.

The following table describes the processes (or commands) executed at run level 3.