When you run multiple applications on your computer, it seems like they are all running simultaneously. In reality, the CPU is rapidly switching between them, giving each process a small amount of processing time.
How the CPU Manages Processes
Each process is allocated a small amount of CPU time called a "time slice". After its time slice, a process is paused, and the CPU moves to the next one. By default, the Linux kernel schedules processes in a round-robin fashion, ensuring every process gets a fair share of CPU time until it completes. The kernel's scheduler is highly efficient at managing these rapid switches.
What is Niceness in Linux
While processes cannot directly control their CPU time, you can influence the kernel's scheduling decisions. This is done by adjusting the linux niceness value of a process. The term "niceness" refers to how "nice" a process is to other processes on the system.
The niceness of a process is represented by a number ranging from -20 (highest priority) to 19 (lowest priority).
- A high niceness value (e.g., 19) means the process is very "nice" and has a low priority, yielding CPU time to others.
- A low or negative niceness value (e.g., -20) means the process is not "nice" and demands more CPU time, giving it a higher priority.
Understanding linux process niceness is key to managing system resources effectively.
Adjusting Process Priority
You can view the current niceness level of running processes using the top command. Look for the NI column, which displays the niceness value.
topTo control the niceness linux value, you can use the nice and renice commands.
Use the nice command to start a new process with a specific niceness level. For example, the following command starts apt upgrade with a niceness of 5.
nice -n 5 apt upgradeTo change the priority of an already running process, use the renice command. The following command changes the niceness of a process with PID 3245 to 10.
renice 10 -p 3245