How does nice and renice commands work internally in Linux?

The nice and renice commands in Linux are used to alter the priority of running processes. They influence the process's nice value, which ranges from -20 (highest priority) to 19 (lowest priority). A lower nice value means higher priority for CPU time.

The nice command is typically used to start a process with a specified nice value. On the other hand, renice is used to change the nice value of an already running process.

How Nice Works Internally

When a process is started with nice, the kernel assigns it the specified nice value. The scheduler uses this value to allocate CPU time among all running processes. A process with a lower nice value gets more CPU time compared to those with higher values. This mechanism allows users to influence the CPU scheduling dynamically.

How Renice Works Internally

The renice command allows users to change the nice value of running processes. When renice is invoked, it finds the process using its PID and updates its nice value accordingly. This change influences the process's scheduling priority without having to stop or restart it.

Example Usage