And what do you do when neither fuser not lsof return any results? Every single time I've had something stuck that refused to umount, I have gotten no help from either of these tools. One recent example was mounting a drive image as a loop device, modifying /etc/fstab, backing out of the mounted device so I could umount it.... and it completely refused.
umount -l
usually works for me
True, but it leaves things behind that can get in way when you go to mount other resources in the same folder. On my desktop I just reboot to clear things up, but on my servers it is usually months between reboots and I have to schedule it.
In that case, why not simply
rm -rf /
😜
Too simple.
For complexity, add a "sudo" :-)