The /etc/inittab file is composed of entries that are position-dependent and have the following format:

Identifier:RunLevel:Action:Command

The colon character (:) is used as a delimiter. To comment out an entry in the /etc/inittab file, add : or # at the beginning of the entry.

Example: The following entry is commented out.

:Identifer:RunLevel:Action:Command

Each entry is delimited by a newline character. A backslash (\) character preceding a newline character indicates the continuation of an entry. There are no limits on the number of entries in the /etc/inittab file. The maximum entry size is 1024 characters. The entry fields are:

Identifier

A string of 1 to 7 characters that uniquely identifies the entry. The ID is used as the job name for the process.

• The identifier must start in column 1 of the file.
• Valid characters are A-Z and 0-9. Lowercase characters are converted to uppercase.
• The identifier must start with an alphabetic character.

The identifier is required; there is no default.

RunLevel

Not supported on z/OS® UNIX. Identifies the run levels in which this entry can be processed. Even though the RunLevel field is not supported, it is in the inittab entry for compatibility with other UNIX implementations. The run level field can be up to 32 alphanumeric characters. If it is specified, it will be checked for validity and the inittab entry will be skipped if it is in error.

Action

Specifies how to handle the process that is started in the command field. The supported actions are:

once

Starts the process and does not wait for it to end. Continues scanning the /etc/inittab file and processes the next entry. When it ends, the process is not restarted.

respawn

Starts the process and does not wait for it to end. Continues scanning the /etc/inittab file and processes the next entry. The process is restarted when it ends. When a process is spawned again, it is restarted with the same file descriptors and environment variables that it was started with originally.

If a process ends due to a shutdown of all fork activity, the process is not restarted until fork activity is re-enabled. If a respawnable process ends and then ends again after being restarted within 15 minutes of its first ending, then message BPXI082D is displayed. The message identifies the process entry and asks whether to try again or ignore the error. A process identified for respawn will not be able to register as a permanent process that can survive a shutdown and restart cycle because the /etc/inittab file will be processed again during restart.

Restriction: Daemons, such as cron, inetd, and sshd (the OpenSSH daemon), cannot be restarted using the respawn attribute. These processes fork themselves. The respawn attribute is associated with the parent process that is started, not the forked child processes.

To check the status of the respawn attribute, issue the D OMVS operator command and check the STATE field. You can also use the -o attr option of the ps shell command, which displays the process attributes.

Tip: To avoid excessive consumption of common storage, limit the number of processes started with the respawn attribute to 100 or fewer.

respfrk

Starts the process and does not wait for it to end. Continues scanning the /etc/inittab file and processes the next entry.

• If the process never issues a fork command, then this action behaves the same way as the respawn action.
• If the process issues a fork, then the respawn attribute is transferred to the forked child process. When the child process ends, the original parent process is spawned. This process will fork itself, thus restarting the daemon process.
• If the original process issues any additional forks, the respawn attribute is not transferred to those forked children. It is only transferred the first time the fork is issued.

The respfrk option is intended for a program that forks itself to create a child process which then continues running while the parent process ends. For example, the cron and inetd daemons are written this way.

This option is not found on any other UNIX platforms.

Restriction: Daemons such as the OpenSSH daemon cannot be respawned with the respfrk attribute. The OpenSSH daemon also forks itself to create a child process which then continues running while the parent process ends. However, it does additional forks before actually forking the daemon process.

wait

Starts the process and waits for it to end. The process is not restarted when it ends. Any subsequent /etc/inittab entries are not processed until this process ends.

Command

Identifies a shell command, script, or executable program to be run. The name must be a fully qualified path name. The entire command is, by default, executed by the shell as:

/bin/sh -c "exec command"

You can change the path name of the target shell via the -sh option in the /etc/init.options file, but if respawn is required, this action is not suggested.