LFCS Question #362: Real Exam Question with Answer & Explanation

Question

You wish to revoke write access for all groups and named users on a file. Which command will make the correct ACL changes?

Options

• Asetfacl x group:*:rx,user:*:rx afile
• Bsetfacl x mask::rx afile
• Csetfacl m mask::rx afile
• Dsetfacl m group:*:rx,user:*:rx afile

Explanation

To revoke write access for all groups and named users on a file, the ACL mask must be modified to exclude write permissions.

Common mistakes.

• A. The -x option is used to remove specific ACL entries, not to modify the permissions of existing entries or the mask itself.
• B. The -x option would attempt to remove the mask entry entirely, rather than modifying its permissions to rx.
• D. While -m is for modifying, specifying group:*:rx,user:*:rx is not the correct syntax or method to universally revoke write access by manipulating the mask; the mask entry itself should be targeted.

Concept tested. Linux ACL mask modification

Reference. https://www.redhat.com/sysadmin/linux-access-control-lists

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