How to use the command cgclassify (with examples)

The cgclassify command is used to move running tasks to specific control groups (cgroups). This can be useful for managing resources, setting priorities, and controlling the behavior of processes within a system. In each use case below, we will explore different scenarios where the cgclassify command is used.

Use case 1: Moving a process to a specific control group in the CPU hierarchy

Code:

cgclassify -g cpu:student 1234

Motivation: In this scenario, we want to move a process with a specific PID (1234) to the control group “student” in the CPU hierarchy. This can be helpful in scenarios where we want to allocate specific CPU resources to a group of processes.

Explanation:

• cgclassify is the command used to move running tasks to specific cgroups.
• -g cpu:student specifies the control group we want to move the process to, in this case, “student” in the CPU hierarchy.
• 1234 is the PID of the process we want to move.

Example output: If successful, the output will not return any error messages. The process with PID 1234 will now belong to the “student” control group in the CPU hierarchy.

Use case 2: Moving a process to control groups based on a configuration file

Code:

cgclassify 1234

Motivation: In this use case, we want to move a process with a specific PID (1234) to control groups based on the /etc/cgrules.conf configuration file. This allows us to define the control group for a process without specifying it directly in the command.

Explanation:

• cgclassify is the command used to move running tasks to specific cgroups.
• 1234 is the PID of the process we want to move.

Example output: If the process matches a rule defined in the /etc/cgrules.conf configuration file, it will be moved to the specified control group accordingly. The output will not return any error messages if successful.

Use case 3: Moving a process to a specific control group in the CPU hierarchy with the –sticky flag

Code:

cgclassify --sticky -g cpu:/student 1234

Motivation: In this scenario, we want to move a process with a specific PID (1234) to the control group “student” in the CPU hierarchy, while preserving the control group even if it matches a rule defined in the /etc/cgrules.conf configuration file. This is useful when we want to ensure that the process and its children remain within the specified control group.

Explanation:

• cgclassify is the command used to move running tasks to specific cgroups.
• --sticky is the option used to preserve the control group even if it matches a rule in the /etc/cgrules.conf configuration file.
• -g cpu:/student specifies the control group we want to move the process to, in this case, “student” in the CPU hierarchy.
• 1234 is the PID of the process we want to move.

Example output: If successful, the output will not return any error messages. The process with PID 1234 will belong to the “student” control group in the CPU hierarchy and won’t be affected by rules in the /etc/cgrules.conf configuration file.

Conclusion:

The cgclassify command offers a flexible way to manage cgroups and allocate resources to running tasks. With different options and arguments, it allows the movement of processes to specific control groups based on various criteria. This can be helpful in resource management, setting priorities, and controlling the behavior of processes within a system.