2.11 Exercises

Chapter 3. System Initialization and Boot

A support specialist must understand the system initialization process, common startup errors, and how to customize the startup of software. This chapter introduces the concepts needed to better understand this process.

During system startup, after the root file system has been mounted in the pre-initialization process, the following sequence of events occurs:

1. The init command is run as the last step of the startup process.

2. The init command attempts to read the /etc/inittab file.

3. If the /etc/inittab file exists, the init command attempts to locate an initdefault entry in the /etc/inittab file.
   1. If the initdefault entry exists, the init command uses the specified run level as the initial system run level.

   2. If the initdefault entry does not exist, the init command requests that the user enter a run level from the system console (/dev/console).

   3. If the user enters an S, s, M or m run level, the init command enters maintenance run level. These are the only run levels that do not require a properly formatted /etc/inittab file.

4. If the /etc/inittab file does not exist, the init command places the system in the maintenance run level by default.

5. The init command rereads the /etc/inittab file every 60 seconds. If the /etc/inittab file has changed since the last time the init command read it, the new commands in the /etc/inittab file are executed.

3.1 The /etc/inittab File