NewJokeCity

umount /opt/backup

umount: /opt/backup: device is busy

Use following command to see who’s using the device

fuser -u /opt/backup

/opt/backup:         31493c(username)

Use following command too kill process

fuser -mk /opt/backup

option -k to kill and option -m to allow you to specify the filesystem by name

Now you can issue the umount command again, and it works as expected