The file /srv/reports/q3.txt is rw-r----- and owned by alice:staff. Everyone in staff must now be able to edit it, and nothing else about its mode may change. Which command does exactly that?
LPIC-1 Exam 101-500, objective 104. Devices, Linux filesystems, filesystem hierarchy standard easy
Machine-checked — no person has signed for it. This question was read against the source cited below by an automated pass, which found no contradiction. That is a weaker claim than it sounds: the same kind of process wrote the question, so it can confirm its own mistake.
Treat it as a good draft rather than as settled fact, and read the source below before you rely on it. It is not used in mock exams here — only questions a person has signed for are.
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 g+w /srv/reports/q3.txt
Correct. Symbolic mode with + adds one permission to one class and leaves every other bit untouched, giving rw-rw----.
Not correct chmod 664 /srv/reports/q3.txt
Wrong. An octal mode is absolute, and 664 is rw-rw-r--, which grants read access to everybody else as well — a change the question forbids.
Not correct chmod +w /srv/reports/q3.txt
Wrong. With no class named, + applies to all of u, g and o, restricted by the current umask, so what it ends up doing depends on a setting you cannot see in the command.
Not correct chmod u+w /srv/reports/q3.txt
Wrong class. u is the owner, who already has write permission, so this command changes nothing at all.
Why
Symbolic modes are written as class, operator, permissions: the classes are u, g, o and a; the operators are + to add, - to remove and = to set exactly. + and - are relative, so they preserve the bits they do not mention, while = and any octal mode are absolute and overwrite the whole set. That is the rule to reach for whenever a question says one permission must change and the rest must survive.
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.
More questions on this objective
- A new disk /dev/sdb has no partition table at all. Which command writes an empty GPT partition table onto it without dropping you into an interactive editor? machine-checked
- You need the partition /dev/sdc1 on a USB stick to carry a FAT32 filesystem so that Windows machines can read and write it. Which command creates it? machine-checked
- You have just run `mkswap /dev/sdb2`. Which command makes the kernel start using that swap area immediately, without a reboot? machine-checked
- Why is it dangerous to run e2fsck against an ext4 filesystem that is currently mounted read-write? machine-checked
- On an ext4 filesystem at /dev/sda1 you want an automatic check to be forced after every 30 mounts. Which command sets that? machine-checked
- `df -h /var` reports the filesystem 100% full, but `du -sh /var` accounts for only about half that space. Nothing is hidden under a mount point. What is the most likely explanation? machine-checked
All questions on Devices, Linux filesystems, filesystem hierarchy standard