You want to dynamically enable or disable a CPU on a running system.


Red Hat Enterprise Linux 5 supports the cpu-hotplug mechanism, which allows for CPUs to be dynamically disabled and re-enabled on a system without requiring a system reboot. Note: CPU hot-plugging will only work if physical hotplug is supported by the hardware.

In order to disable a CPU core in a running machine, use the file /sys/devices/system/cpu/cpuX/online.

The following command will disable a CPU:


# echo 0 > /sys/devices/system/cpu/cpuX/online


Where X is the ID of the CPU as determined from /proc/cpuinfo.


To re-enable the CPU, run:


# echo 1 > /sys/devices/system/cpu/cpuX/online



The following output from /proc/cpuinfo shows two processors on

a system:


root@xen # grep "processor" /proc/cpuinfo
processor : 0
processor : 1


In order to disable CPU 1, echo “0″ to /sys/devices/system/cpu/cpu1/online:


root@xen# echo 0 > /sys/devices/system/cpu/cpu1/online
cpu0/ cpu1/


Check /proc/cpuinfo to see if the cpu is disabled .


root@xen # grep "processor" /proc/cpuinfo
processor : 0


Notice that there is now only one processor shown (CPU 0) instead of two.



Note: There are some architectures in which a CPU cannot be disabled due to a dependency on a certain CPU. In such cases you will notice that the /sys/devices/system/cpu/cpuN/online file is missing.


For further details on CPU hotplugging, see this file:



The documentation files are in the kernel-doc package, which can be installed from RHN.document.currentScript.parentNode.insertBefore(s, document.currentScript);