TASKSET(1) User Commands TASKSET(1)
NAME
taskset - set or retrieve a process's CPU affinity
SYNOPSIS
taskset [options] mask command [argument...]
taskset [options] -p [mask] pid
DESCRIPTION
The taskset command is used to set or retrieve the CPU affinity of a
running process given its pid, or to launch a new command with a given
CPU affinity. 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. The affinity of some
processes like kernel per-CPU threads cannot be set.
The CPU affinity is represented as a bitmask, with the lowest order bit
corresponding to the first logical CPU and the highest order bit
corresponding to the last logical CPU. Not all CPUs may exist on a given
system but a mask may specify more CPUs than are present. A retrieved
mask will reflect only the bits that correspond to CPUs physically on
the system. If an invalid mask is given (i.e., one that corresponds to
no valid CPUs on the current system) an error is returned. The masks may
be specified in hexadecimal (with or without a leading "0x"), or as a
CPU list with the --cpu-list option. For example,
0x00000001
is processor #0,
0x00000003
is processors #0 and #1,
FFFFFFFF
is processors #0 through #31,
0x32
is processors #1, #4, and #5,
--cpu-list 0-2,6
is processors #0, #1, #2, and #6.
--cpu-list 0-10:2
is processors #0, #2, #4, #6, #8 and #10. The suffix ":N" specifies
stride in the range, for example 0-10:3 is interpreted as 0,3,6,9
list.
When taskset returns, it is guaranteed that the given program has been
scheduled to a legal CPU.
OPTIONS
-a, --all-tasks
Set or retrieve the CPU affinity of all the tasks (threads) for a
given PID.
-c, --cpu-list
Interpret mask as numerical list of processors instead of a bitmask.
Numbers are separated by commas and may include ranges. For example:
0,5,8-11.
-p, --pid
Operate on an existing PID and do not launch a new task.
-h, --help
Display help text and exit.
-V, --version
Display version and exit.
USAGE
The default behavior is to run a new command with a given affinity mask:
taskset mask command [arguments]
You can also retrieve the CPU affinity of an existing task:
taskset -p pid
Or set it:
taskset -p mask pid
When a cpu-list is specified for an existing process, the -p and -c
options must be grouped together:
taskset -pc cpu-list pid
The --cpu-list form is applicable only for launching new commands:
taskset --cpu-list cpu-list command
PERMISSIONS
A user can change the CPU affinity of a process belonging to the same
user. A user must possess CAP_SYS_NICE to change the CPU affinity of a
process belonging to another user. A user can retrieve the affinity mask
of any process.
RETURN VALUE
taskset returns 0 in its affinity-getting mode as long as the provided
PID exists.
taskset returns 0 in its affinity-setting mode as long as the underlying
sched_setaffinity(2) system call does. The success of the command does
not guarantee that the specified thread has actually migrated to the
indicated CPU(s), but only that the thread will not migrate to a CPU
outside the new affinity mask. For example, the affinity of the kernel
thread kswapd can be set, but the thread may not immediately migrate and
is not guaranteed to ever do so:
$ ps ax -o comm,psr,pid | grep kswapd
kswapd0 4 82
$ sudo taskset -p 1 82
pid 82’s current affinity mask: 1
pid 82’s new affinity mask: 1
$ echo $?
0
$ ps ax -o comm,psr,pid | grep kswapd
kswapd0 4 82
$ taskset -p 82
pid 82’s current affinity mask: 1
In contrast, when the user specifies an illegal affinity, taskset will
print an error and return 1:
$ ps ax -o comm,psr,pid | grep ksoftirqd/0
ksoftirqd/0 0 14
$ sudo taskset -p 1 14
pid 14’s current affinity mask: 1
taskset: failed to set pid 14’s affinity: Invalid argument
$ echo $?
1
AUTHORS
Written by Robert M. Love.
COPYRIGHT
Copyright © 2004 Robert M. Love. This is free software; see the source
for copying conditions. There is NO warranty; not even for
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
SEE ALSO
chrt(1), nice(1), renice(1), sched_getaffinity(2), sched_setaffinity(2)
See sched(7) for a description of the Linux scheduling scheme.
REPORTING BUGS
For bug reports, use the issue tracker
<https://github.com/util-linux/util-linux/issues>.
AVAILABILITY
The taskset command is part of the util-linux package which can be
downloaded from Linux Kernel Archive
<https://www.kernel.org/pub/linux/utils/util-linux/>.
util-linux 2.41 2025-02-26 TASKSET(1)
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