Ten minutes before a planned database restart you want a warning to appear on the terminals of everyone currently logged in, without initiating any shutdown. Which command sends it?
LPIC-1 Exam 101-500, objective 101. System architecture easy
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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 wall
Correct. wall writes a message to the terminals of all logged-in users who have not disabled messages, and it does nothing else.
Not correct write
Wrong for a broadcast. write sends a message to one named user's terminal, so it would have to be repeated for every session.
Not correct mesg n
Wrong, and the opposite operation. mesg controls whether other users may write to your own terminal; mesg n blocks such messages.
Not correct Appending the notice to /etc/motd
Wrong for this timing. The message of the day is printed by the login process, so only sessions started after the edit would ever see it.
Why
wall reads its message from a command-line argument, a file or standard input and broadcasts it to every terminal whose owner permits messages, prefixed by a banner naming the sender and the time. Root's messages are delivered even to users who have run mesg n. The related commands split the same problem by scope: write for one user, wall for everyone now, motd for everyone at their next login, and `shutdown` for a warning tied to a scheduled event.
Where this comes from
- Cited
- manual page wall(1)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 101 and space the ones you get wrong.
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