Linux uses the priority based scheduling algorithm. It ranks the processes based on their worth and need for processor time. The Linux kernel implements two separate priority ranges.
1. Nice Values:
It is a number between -20 and +19 with a default value of 0. Larger nice values correspond to a lower nice values i.e. it is nice to the other processes in the system. Thus, processes with lower nice values receive a greater proportion of the system processor as compared to processes with a higher nice value. In Mac OS X nice values control over the absolute time-slice. In Linux, it is the control over the proportion of the time-slice.
ps -el commmand gives the processes and their corresponding nice values.
The getpriority and setpriority functions gets and sets the nice values. (http://linux.die.net/man/2/setpriority)
Nice values can be set from the linux command line using the nice command. To set lower priority to a process to avoid slow down of other processes, we can use the following command.
$ nice -n 19 tar cvzf archive.tgz largefile
2. Real-time priority:
These priority values range from 0 to 99 inclusive with default value being 0. Unlike nice values, higher real-time priority values mean higher priority. All real time processes are at a higher real-time priority value than other processes.
The command below gives the list of processes and their real-time priority values under the column marked RTPRIO.
ps -eo state,uid,pid,ppid,rtprio,time,comm
A value of "-" means the process is not real time.
1. Nice Values:
It is a number between -20 and +19 with a default value of 0. Larger nice values correspond to a lower nice values i.e. it is nice to the other processes in the system. Thus, processes with lower nice values receive a greater proportion of the system processor as compared to processes with a higher nice value. In Mac OS X nice values control over the absolute time-slice. In Linux, it is the control over the proportion of the time-slice.
ps -el commmand gives the processes and their corresponding nice values.
The getpriority and setpriority functions gets and sets the nice values. (http://linux.die.net/man/2/setpriority)
Nice values can be set from the linux command line using the nice command. To set lower priority to a process to avoid slow down of other processes, we can use the following command.
$ nice -n 19 tar cvzf archive.tgz largefile
2. Real-time priority:
These priority values range from 0 to 99 inclusive with default value being 0. Unlike nice values, higher real-time priority values mean higher priority. All real time processes are at a higher real-time priority value than other processes.
The command below gives the list of processes and their real-time priority values under the column marked RTPRIO.
ps -eo state,uid,pid,ppid,rtprio,time,comm
A value of "-" means the process is not real time.
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