A backup script must keep running after you close your SSH session. You have not started it yet. Which invocation is designed for exactly this?
LPIC-1 Exam 101-500, objective 103. GNU and Unix commands medium
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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 nohup ./backup.sh &
Correct. nohup makes the process ignore SIGHUP so the hangup sent when the terminal closes does not kill it, and & puts it in the background. Output goes to nohup.out unless redirected.
Not correct ./backup.sh &
Wrong on its own. The & backgrounds the job, but the process is still attached to the terminal's session and can be killed by the SIGHUP sent at logout.
Not correct bg ./backup.sh
Wrong. bg takes a job spec such as %1 for a job that is already stopped; it cannot launch a command, and it does not protect against SIGHUP.
Not correct nice ./backup.sh &
Wrong. nice only changes scheduling priority (by default adding 10 to the nice value). It has no effect on signal handling or terminal attachment.
Why
`nohup cmd &` is the classic pairing: nohup blocks SIGHUP, & returns the prompt. Alternatives are to start the job inside screen or tmux and detach, or to background it and then run `disown` so bash stops tracking it.
Where this comes from
- Cited
- LPI exam objective 103.5
- What it says
- Run processes detached from the terminal so they survive logout.
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 103 and space the ones you get wrong.
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