The nice command in Unix-like operating systems is used to launch a process with a modified scheduling priority, known as a “niceness value.” The niceness value affects how the kernel schedules CPU time for that process relative to others.
How it works:
1. Niceness Value:
Niceness values range from -20 (highest priority) to 19 (lowest priority).
By default, most processes start with a niceness of 0.
A higher niceness value means the process is more “nice” to others, allowing them to have more CPU time, while a lower niceness value means the process demands more CPU time.
2. Command Syntax:
nice [OPTION] [COMMAND [ARG]...]
[OPTION]: You can set the niceness value using -n or specify it directly.[COMMAND [ARG]...]: The command and its arguments you want to execute with the specified niceness.
3. Examples:
- Run a process with a higher niceness (lower priority):
nice -n 10 ./my_program
This starts my_program with a niceness of 10.
- Check the current process’s niceness:
ps -o pid,ni,comm
This displays the process ID (PID), niceness (NI), and command.
- Run a process with a higher priority (lower niceness, e.g., -10):
sudo nice -n -10 ./my_program
Only superusers can set a niceness value below 0.
4. Changing Niceness of Running Processes:
Use the renice command to adjust the niceness of an already running process:
renice -n 5 -p 12345
This changes the niceness of the process with PID 12345 to 5.