error: umount was not found in /proc/mounts

I need to change NFS configuration recently， so umount original device firstly.

But I encuntered one error “umount was not found in /proc/mounts”

I checked file /proc/mounts. there is nothing about this device. but if the information abount

this device in /porc/mounts, this device can be umounted.

After searching many materials, I found I can execute “umount -l mount_point” to umount the abnormal

umont.

for example

umount -l /mnt/hda5

parameter -l

option –l is not to umount right now，this option will execute umount after the dictionary free.

It’s better check which PID occupies through command “ps -ef “, kill this pid , and then execute “umount -l”