i was finishing up a job with a compact flash when, trying to unmount it:

#> umount /dev/sda2 
umount: it seems /dev/sda2 is mounted multiple times

Looking at what mount says:

#> mount | column -t | grep sda2
/dev/sda2  on  /mnt/flashrw  type  ext3      (rw,nosuid,nodev)
/dev/sda2  on  /mnt/flashrw  type  ext3      (rw,nosuid,nodev,user=myuser)

it seems that I accidentally mounted the same device on the same location (though in two different ways).

I tried to unmount it many times also with:

#> umount /mnt/flashrw 
umount: it seems /mnt/flashrw is mounted multiple times

with no luck. Finally, I tried:

#> sudo umount -f /dev/sda2

but umount locked completely.

So the question is: and now?


Try running this command:

sudo umount /mnt/flashrw
  • 3
    Yup, fixed it for me. That was the most misleading error message I have seen in a a while. – Laurens Holst Jan 13 '13 at 1:45
  • what if you do not have sudo access on the server – user5359531 Jun 18 '18 at 15:26

Most probably it was a kernel bug due to an unstable patch interaction. I was using a 3.4.11 vanilla kernel patched with the corresponding RT-PREEMPT patch by Ingo Molnar.

Due to a severe memory leak, I moved to 3.6.4 vanilla + RT-PREEMPT patch and now the system seems to be really stable. The problem has never presented again. Hope this may help someone in the future.

  • Why is this marked as the answer? – JamesH Dec 15 '17 at 22:51
  • 1
    Because it was what really was happening to me. It was not the beginner use case "I can't umount my usb pen and I don't even know about the existence of lsof or fuser", it was a kernel issue due to an unofficial (and problematic) kernel patch applied to a custom kernel. – Avio Dec 18 '17 at 13:43

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