umount: device is busy

sometimes, when i try to umount a mounted device, the following error occurs.

xwang@node1 ~ $ umount /mnt/ps4000e/home
umount.nfs: /mnt/ps4000e/home: device is busy
umount.nfs: /mnt/ps4000e/home: device is busy

No one is logged in except myself which I do not use that directory and no other user’s job is running. It is really a mystery to figure out which process causes the “device is busy”. Use google, I found the solution at
The solution is to use fuser to find out.

xwang # fuser -m /mnt/ps4000e/home/
/mnt/ps4000e/home/: 7706c

See the manual man fuser for full description of this command. I guess 7706 is the process id which is currently uses the mounted device. Not sure the following letter ‘c’ stands for. So use ps to find out the process.

xwang # ps 7706
7706 ? Ss 0:00 /usr/bin/orted --daemonize ....

Now the reason is obvious. I started an mpi job before and it does not end abnormally. The orted is the administration process started by root and it does not exit. So after the process was killed, the device was able to be detached.

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