`umount /mnt/data` fails with 'target is busy'. Which command lists every process holding a file open anywhere on that mounted filesystem, so you can see who to stop first?
LPIC-1 Exam 102-500, objective 110. Security medium
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How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Correct fuser -m /mnt/data
Correct. -m treats the argument as a mounted filesystem and reports every process using any file on it, which is precisely the set that keeps the mount busy.
Not correct fuser /mnt/data
Wrong. Without -m the argument is taken as a single file, so only processes using that directory itself, for instance one with its working directory there, are reported.
Not correct fuser -k /mnt/data
Wrong twice over: -k sends SIGKILL to the processes found rather than merely listing them, and without -m it still examines only the named directory.
Not correct lsof -i /mnt/data
Wrong. -i selects internet sockets and takes a host or port specification; combining it with a path does not enumerate open files on a filesystem.
Why
A mount is busy while any process holds an open file, working directory or memory mapping on it. fuser -m NAME interprets NAME as a filesystem, or as the block device backing one, and lists every process using it, marking each PID with the kind of access: c for current directory, e for a running executable, r for root directory and m for a mapped file (f and F, for open files, are omitted from the default display). lsof +D /mnt/data answers the same question by walking the tree. Reserve fuser -k for when you have already decided the processes may die.
Where this comes from
- Cited
- manual page fuser(1)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 110 and space the ones you get wrong.
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