How to use the command rc-update (with examples)

The rc-update command is used to add and remove OpenRC services to and from runlevels in a Linux system. It provides a convenient way to manage the services that are run at startup or at specific runlevels. This article will illustrate various use cases of the rc-update command using examples.

Use case 1: List all services and the runlevels they are added to

Code:

rc-update show

Motivation: By listing all services and the runlevels they are added to, you can get an overview of the services that are configured to start automatically on your system. This can help in troubleshooting startup issues or understanding the dependencies between different services.

Explanation: The rc-update show command displays a list of services along with the runlevels they are added to. Runlevels in OpenRC represent various system states and determine which services are started or stopped when the system transitions to that particular runlevel.

Example output:

acpid   | default                               
avahi-daemon | default                             
dbus    | default                               
devfs   | sysinit                               
...

Use case 2: Add a service to a runlevel

Code:

sudo rc-update add service_name runlevel

Motivation: Adding a service to a specific runlevel ensures that the service is started or stopped when the system transitions to that runlevel. This can be useful when you want to control the behavior of a service based on the current system state.

Explanation:

• sudo is used to run the rc-update command with administrative privileges.
• add is the sub-command used to add a service to a runlevel.
• service_name is the name of the service you want to add.
• runlevel is the runlevel to which the service should be added.

Example:

sudo rc-update add nginx default

This command adds the nginx service to the default runlevel, ensuring that it starts automatically when the system transitions to the default runlevel.

Use case 3: Delete a service from a runlevel

Code:

sudo rc-update delete service_name runlevel

Motivation: Removing a service from a specific runlevel prevents it from being started or stopped when the system transitions to that runlevel. This can be useful when you no longer require a service to run at a particular system state.

Explanation:

• sudo is used to run the rc-update command with administrative privileges.
• delete is the sub-command used to remove a service from a runlevel.
• service_name is the name of the service you want to remove.
• runlevel is the runlevel from which the service should be removed.

Example:

sudo rc-update delete nginx default

This command removes the nginx service from the default runlevel, ensuring that it no longer starts automatically when the system transitions to the default runlevel.

Use case 4: Delete a service from all runlevels

Code:

sudo rc-update --all delete service_name

Motivation: Deleting a service from all runlevels ensures that it is completely removed from the system’s startup configuration. This can be useful when you want to disable a service from starting automatically at any runlevel.

Explanation:

• sudo is used to run the rc-update command with administrative privileges.
• --all is an option that specifies all runlevels. It indicates that the service should be removed from all runlevels.
• delete is the sub-command used to remove a service from runlevels.
• service_name is the name of the service you want to remove.

Example:

sudo rc-update --all delete nginx

This command removes the nginx service from all runlevels, ensuring that it no longer starts automatically when the system transitions to any runlevel.

Conclusion:

The rc-update command is a powerful tool for managing OpenRC services and their runlevel configurations in a Linux system. By using the various sub-commands and options provided by rc-update, users can easily add or remove services from specific runlevels, view the current state of services, and disable services from starting automatically. These capabilities make it a valuable command for system administrators and users who want to have control over the services running on their system.