A copied web tree under /srv/www has inconsistent modes. Every directory must become traversable and readable by everyone, and every file readable by everyone, but no data file may be made executable. Which single command achieves that?
LPIC-1 Exam 101-500, objective 104. Devices, Linux filesystems, filesystem hierarchy standard hard
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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 chmod -R a+rX /srv/www
Correct. The capital X sets the execute bit only on directories and on files that already have execute set for at least one class, which is exactly the distinction wanted.
Not correct chmod -R a+rx /srv/www
Wrong. Lowercase x makes every file executable too, so HTML and image files end up with the execute bit for no reason.
Not correct chmod -R 755 /srv/www
Wrong for two reasons: it makes every ordinary file executable, and being absolute it also strips permissions the tree may already need, such as group write.
Not correct chmod -R a+r /srv/www
Wrong. Files become readable, but without the execute bit a directory cannot be entered, so nothing inside can be reached even though the names could in principle be listed.
Why
On a directory, execute means the right to traverse it and to resolve names within it, which is why a recursive fix must give directories x while leaving data files without it. chmod's X permission letter is written precisely for this case: it means execute for directories, and for other files only when some execute bit is already present. Combined with -R and a relative operator it is the safe way to repair a tree, since an octal mode would overwrite every bit rather than adjusting the ones named.
Where this comes from
- Cited
- manual page chmod(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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