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I want to disable 3 CPU cores and run my processor on a single core. I have used command:maxcpus=1. But after this I executed this command ls /sys/devices/system/cpu. It still shows cpu0,cpu1,cpu2,cpu3.

I also tried :echo 0 > /sys/devices/system/cpu3/online but I get the following error: no such file or directory.

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It is unclear where you put the maxcpus=1 commmand? Did you put that string in grub.cfg as a boot option? (Please update your question instead of answering in comments). – Anthon Jul 21 '14 at 7:24
    
I am using freescale IMx6 sabreauto board on linux OS.I executed the command on a terminal emulator "gtkterm" – user3818847 Jul 21 '14 at 7:41
    
With this command echo 0 > /sys/devices/system/cpu3/online I am able to see cpu3 shutdown. Now what I want know is, should I reboot the system for the changes to effect or I can continue without rebooting – user3818847 Jul 21 '14 at 7:45
    
AFAIK you should specify maxcpus=1 as a parameter to the kernel (i.e. when you are in grub). Edit '/etc/defaults/grub' to add it to the kernel parameters, run 'update-grub' and reboot. That will make things persistent, i.e. with only one CPU on Linux startup. – Anthon Jul 21 '14 at 8:55
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@user3818847 what distro are you using? Modifying the boot parameters (to pass maxcpus=1) varies by distro. Also the /sys path you have is simply the wrong one, the correct path is /sys/devices/system/cpu/cpu3/online. – Patrick Jul 21 '14 at 13:00
up vote 19 down vote

As Patrick has indicated in a comment, you got the path under /sys wrong.

echo 0 > /sys/devices/system/cpu/cpu3/online

If you want to switch all CPUs off (except cpu0 which can't be switched off):

for x in /sys/devices/system/cpu/cpu*/online; do
  echo 0 >"$x"
done

Typing maxcpus=1 at a shell prompt has no effect. More precisely, it sets the variable maxcpus to the value 1 in that shell, which doesn't have any other effect. You can set the number of CPUs at boot time by passing maxcpus as a kernel parameter. For that, you have to change your bootloader configuration (e.g. to change the kernel command line in U-Boot).

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Thank you for the suggestions. It worked with the command suggested by you – user3818847 Jul 22 '14 at 9:25
    
This is at least somewhat kernel-specific. I'm running kernel 3.6.6, and there's no such files; you instead use the single /sys/devices/system/cpu/online and ./offline files to control all the cores. – Daniel Griscom May 9 '17 at 21:22

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