Linux taskset to retrieve or set a processess CPU affinity

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Q. How do I use Linux (RHEL) taskset command to set or get the CPU affinity of a running process given its PID or to launch a new COMMAND with a given CPU affinity?

A. You need to use taskset command. CPU affinity is a scheduler property that “bonds” a process to a given set of CPUs on the system. The Linux scheduler will honor the given CPU affinity and the process will not run on any other CPUs. Note that the Linux scheduler also supports natural CPU affinity: the scheduler attempts to keep processes on the same CPU as long as practical for performance reasons. Therefore, forcing a specific CPU affinity is useful only in certain applications.

Retrieve the CPU affinity of an existing task

The general syntax is as follows:
taskset -p [pid]
To retrieve the CPU affinity of an existing task (PID 12345), enter:
# taskset -p 12345

Use taskset command to CPU affinity

The general syntax is as follows:
taskset -c [0,1,2,3..N] [pid]

  • -c 0,1,2,..N : The masks are typically given in hexadecimal. For example, 0x00000001 is processor #0, 0x00000003 is processors #0 and #1 etc. However -c option allows you to specifiy a numerical list of processors instead of a bitmask. The list may contain multiple items, separated by comma, and ranges. For example, 0,5,7,9-11.
  • pid : Process / program ID

For example set PID 12345 on 2-3 CPU, enter:
# taskset -c 2,3 12345

Posted by: Vivek Gite

The author is the creator of nixCraft and a seasoned sysadmin, DevOps engineer, and a trainer for the Linux operating system/Unix shell scripting. Get the latest tutorials on SysAdmin, Linux/Unix and open source topics via RSS/XML feed or weekly email newsletter.

3 comment

  1. I wanted to use taskset to attach cpu cores to specific processes.
    I followed your example. But it does not work and returns the

    taskset -c 5 29885
    execvp: no such file or dir
    failed to execute 29885

    Also trying to execute taskset at the mpi command line like
    mpirun -np 2 taskset -c 4,5 test output &
    simply does not work.

    Any help most greatfully appreciated.

  2. taskset sets the processor affinity of a NEW process — one that you specify as the rest of the parameters on the command line. like the ‘nice’ program. it is giving you an error because you are telling to to run the command 29885. to modify the affinity of an existing process, use the -p option. ex: taskset -p 1 29885.

  3. Correct Syntax is as below

    [root@vikasbox ~]# taskset -c -p 1 31777
    pid 31777’s current affinity list: 0
    pid 31777’s new affinity list: 1
    [root@vikasbox ~]#

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