How to use the command 'telinit' (with examples)

Telinit is a command that is used to change the SysV runlevel, power off or reboot a machine, reload daemon configuration, or enter rescue mode. This article will provide a step-by-step guide with examples on how to use the telinit command for various use cases.

Use case 1: Power off the machine

Code:

telinit 0

Motivation: The power-off command is used to gracefully shut down the machine. It sends a signal to all processes, allowing them to terminate cleanly before the system powers off.

Explanation: The 0 argument in the telinit command represents the runlevel of powering off the machine. When telinit 0 is executed, the command interprets this as a request to power off the machine.

Example output:

Broadcast message from root@hostname
	The system is going down for power off NOW!

Use case 2: Reboot the machine

Code:

telinit 6

Motivation: Rebooting the machine is often necessary when making significant changes or applying updates to the system. It allows the system to start fresh with the updated configuration.

Explanation: The 6 argument in the telinit command represents the runlevel of rebooting the machine. When telinit 6 is executed, the command initiates a system reboot.

Example output:

Broadcast message from root@hostname
	The system is going down for reboot NOW!

Use case 3: Change SysV run level

Code:

telinit 2|3|4|5

Motivation: Changing the SysV run level allows users to control the behavior and services running on the system. By switching to different run levels, specific sets of services can be started or stopped.

Explanation: The 2|3|4|5 argument in the telinit command represents the runlevel to be changed to. Each of these run levels corresponds to a specific configuration of services in the sysvinit system. Runlevels 2-5 are user-configurable.

Example output:

Switching to runlevel 5

Use case 4: Change to rescue mode

Code:

telinit 1

Motivation: Entering rescue mode is helpful in troubleshooting and fixing system issues. It provides a minimal environment with a limited set of services running, allowing users to diagnose and rectify problems.

Explanation: The 1 argument in the telinit command represents the runlevel for entering rescue mode. By executing telinit 1, the system transitions into a single-user mode with a minimal set of services running.

Example output:

Switching to runlevel 1

Use case 5: Reload daemon configuration

Code:

telinit q

Motivation: Reloading the daemon configuration is useful when changes are made to system services or configurations. It ensures that the updated configuration is applied without requiring a full system restart.

Explanation: The q argument in the telinit command triggers a reload of the daemon configuration. When executed, the command sends a signal to the init process to re-read its configuration and reload the necessary daemons.

Example output: (No output is usually displayed when the daemon configuration is successfully reloaded)

Use case 6: Do not send a wall message before reboot/power-off (6/0)

Code:

telinit --no-wall value

Motivation: By default, telinit sends a wall message to all logged-in users before initiating a system reboot or power-off. However, sometimes it may be necessary to skip the wall message, especially during automated processes or when user notification is not required.

Explanation: The --no-wall flag in the telinit command is used to prevent a wall message from being sent. The value argument represents the runlevel (6 for reboot, 0 for power-off) where the wall message is to be skipped.

Example output:

The system will be rebooted.

Conclusion

In this article, we explored various use cases of the ’telinit’ command. We learned how to power off or reboot the machine, change the SysV run level, enter rescue mode, reload the daemon configuration, and skip the wall message before reboot or power-off. Understanding these use cases can help users effectively manage and control their systems.