How to Use the Command 'openrc' (with Examples)

OpenRC is a service management system used predominantly in Unix-like operating systems, such as Gentoo Linux. It provides a mechanism to start, stop, pause, and monitor the status of system services and initialize the system in various runlevels. Unlike the more prevalent systemd, OpenRC is lightweight and less complex, making it ideal for users who prefer a more minimalist and traditional approach to service management. Below, we will explore specific use cases of the openrc command, illustrating how to change the system’s runlevel effectively.

Use case 1: Changing to a Specific Runlevel

Code:

sudo openrc runlevel_name

Motivation:

Switching to a different runlevel can be essential for various administrative tasks such as troubleshooting, maintenance, or system upgrades. For example, you might want to switch to a single-user runlevel to perform system backups without other users potentially interrupting the process. By using OpenRC, you can make this transition smoothly, ensuring that only the services appropriate for the selected runlevel are running.

Explanation:

• sudo: This command prefix is used to execute OpenRC with superuser privileges, which is often necessary for making significant system changes such as altering the runlevel.

• openrc: This is the primary command that invokes the OpenRC service manager and is responsible for handling different service management tasks.

• runlevel_name: This argument specifies the target runlevel to which the system should transition. Each runlevel has a defined purpose and set of services associated with it, such as ‘default’, ’nonetwork’, or ‘single’ for various levels of system operation.

Example Output:

Upon execution, OpenRC will halt services from the current runlevel and initiate those specified for the new runlevel. You might see something similar to the following consoling output as services are started or stopped:

Stopping service: sshd ...                    [ ok ]
Stopping service: network-manager ...         [ ok ]
Starting service: local ...                   [ ok ]
Switched to runlevel: runlevel_name

Use case 2: Changing to a Specific Runlevel Without Stopping Existing Services

Code:

sudo openrc --no-stop runlevel_name

Motivation:

In certain operational scenarios, you may need to elevate the service level (or runlevel) of your system without interrupting services currently in use. For instance, during routine maintenance, you might need to enable additional services in preparation for an upgrade but cannot afford to disrupt the current network or user-facing services. The --no-stop option allows for a smooth transition by adding new services without withdrawing already active ones.

Explanation:

• sudo: As with the first use case, superuser privileges are needed to execute command lines impacting system behavior at a foundational level.

• openrc: Invokes the OpenRC service manager to handle runlevel transitions.

• --no-stop: This command-line option specifies that the OpenRC should refrain from stopping services that are running currently. It ensures all existing services remain uninterrupted, adding new services defined for the new runlevel.

• runlevel_name: Once again, this argument denotes the target runlevel, dictating which services should additionally be started.

Example Output:

Upon running this command, the system will output information about newly started services, leaving the existing ones operational:

Starting service: httpd ...                 [ ok ]
Starting service: ntpd ...                  [ ok ]
Runlevel changed to: runlevel_name without stopping existing services

Conclusion:

By utilizing OpenRC, system administrators gain fine control over their service management and runlevel transitions, whether requiring a complete switchover of services or an augmentation of current operations. These versatile options can optimize system performance and reliability in varying circumstances, ranging from maintenance to troubleshooting to full-scale upgrades. OpenRC’s lightweight and traditional design provides an ideal solution for those who appreciate simplicity in their service management tools.