alice owns notes.txt and wants to hand it over to bob. Her `chown bob notes.txt` fails with 'Operation not permitted'. What is the explanation?
LPIC-1 Exam 101-500, objective 104. Devices, Linux filesystems, filesystem hierarchy standard medium
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The options
Correct On Linux only the superuser may change a file's owner, so alice cannot give a file away even though she owns it.
Correct. Changing the owning user is a privileged operation, guarded by CAP_CHOWN, which ordinary users do not hold.
Not correct The file's mode must include write permission for bob before the ownership can move to him.
Wrong. The permission bits on the file play no part in the check; the restriction is on who may call chown at all.
Not correct chown changes only the group, so alice should have used `chown bob:bob notes.txt` instead.
Wrong. chown changes the user, and optionally the group after a colon. Adding the group would fail with the same error for the same reason.
Not correct bob must be a member of one of alice's groups before he can be made the owner.
Wrong. Group membership governs whether the OWNER may hand a file to a GROUP, not who may become the owning user.
Why
Two different rules are easy to confuse. Changing the owning user is root-only, because otherwise a user could dump files onto someone else's disk quota or plant a file they no longer control. Changing the owning group is allowed to the file's owner, but only to a group they are themselves a member of, which is what chgrp and `chown :group` do. Root is bound by neither.
Where this comes from
- Cited
- manual page chown(1)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 104 and space the ones you get wrong.
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