In a bash shell, `jobs` reports job 1 running in the background and job 2 stopped. You want job 2 to take over the terminal so you can interact with it. Which command does that?
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 fg %2
Correct. fg moves the named job into the foreground and sends it SIGCONT, so a stopped job resumes and the shell waits for it.
Not correct bg %2
Wrong. bg also resumes a stopped job with SIGCONT, but leaves it running in the background, where it still cannot read from the terminal.
Not correct kill -CONT %2
Wrong in effect. The signal does restart the process, but the shell still regards the job as a background job, so it does not get the terminal.
Not correct wait %2
Wrong. wait only makes the shell wait on the job's status; it never resumes a stopped job and never hands it the terminal, so job 2 stays exactly where it was.
Why
Job control identifies jobs by a jobspec beginning with %, so %2 is job number 2, %+ or %% the current job and %- the previous one. fg brings a job to the foreground and resumes it; bg resumes it in the background; both send SIGCONT to a job that was stopped by Ctrl+Z. Only the foreground job is connected to the terminal for input, which is the property the question turns on.
Where this comes from
- Cited
- manual page bash(1)
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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