Here is the command I issued:

root@vishal-Think:~# echo "0" > /proc/irq/0/smp_affinity

And here is the error:

-bash: echo: write error: Input/output error

The ls command shows that root has write permissions:

root@vishal-Think:~# ls -l /proc/irq/0/smp_affinity
-rw------- 1 root root 0 May 21 16:30 /proc/irq/0/smp_affinity

Please tell me how I could fix this.

Another question of mine is that even after disabling irqbalance and rebooting the machine, I still see interrupts going to cpus other than cpu0. Why could that be happening?

2 Answers 2


IRQ 0 is timer interrupt and is handled only by core 0. This can not be moved to other cores.


/proc is a virtual file system and although the information appears to be a file, you do not write to the files.

See http://www.tldp.org/LDP/Linux-Filesystem-Hierarchy/html/proc.html

I am not sure what the problem is with your hardware or how to fix it. Please update your question describing the problem and what you did to generate that error message.

  • As shown in my post, I tried to echo into /proc/irq0/smp_affinity. Is that not the correct method? If not, then how do I change the interrupt affinity in Ubuntu. May 22, 2014 at 14:16
  • That is a very broad question and I would refer you to the linux kerenl documentation. On this site, I suggest you identify your hardware and describe the problem. What makes you think you need to change the interrupt affinity?
    – Panther
    May 22, 2014 at 14:52
  • normally the echo as root should work temporarily. Obviously you have a problem, hard to know the best solution, may well be to file a bug report against the linux kernel.
    – Panther
    May 22, 2014 at 14:56

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