`umount /mnt/data` fails with 'target is busy'. Select the TWO commands that help you find out which processes are keeping it busy.
LPIC-1 Exam 101-500, objective 104. Devices, Linux filesystems, filesystem hierarchy standard medium
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The options
Choose 2.
Not correct df -h /mnt/data
Wrong. df reports how full the filesystem is. It says nothing about which processes hold it open.
Not correct blkid /mnt/data
Wrong. blkid identifies block devices by UUID, label and filesystem type. It is for identification, not for finding users of a mount.
Correct lsof /mnt/data
Correct. lsof lists open files; given a mount point it reports every process with a file open under it, including a shell whose working directory is simply inside the tree.
Not correct mount -a
Wrong, and counterproductive. mount -a mounts everything eligible in /etc/fstab; it is the opposite of what you are trying to do.
Correct fuser -m /mnt/data
Correct. -m interprets the argument as a mount point and lists the PIDs using that filesystem. Adding -v explains how each is using it, and -k would kill them.
Why
A filesystem is busy while any process has a file open on it or has a working directory inside it. lsof and fuser -m both identify the culprits. `umount -l` (lazy) detaches the tree immediately and cleans up when the last reference closes; it hides the problem rather than solving it, and `umount -f` is mainly for unreachable network mounts.
Where this comes from
- Cited
- LPI exam objective 104.3
- What it says
- Unmount filesystems and diagnose why a filesystem is busy.
Practise this
Reading one question is not practice. The trainer will draw a set from objective 104 and space the ones you get wrong.