Every entry in root's crontab writes progress messages to standard output, so root's mailbox fills up with one message per run. You want the jobs to keep running and keep writing their output, but you want cron to stop mailing it. Which line, placed near the top of that crontab, achieves this?
LPIC-1 Exam 102-500, objective 107. Administrative tasks 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 MAILTO=""
Correct. MAILTO set to the empty string tells cron not to send mail at all for entries that follow it in the file.
Not correct MAILTO=/dev/null
Wrong. The value of MAILTO is treated as a mail recipient, not as a file. Cron would hand the message to the MTA addressed to a user called /dev/null, which merely relocates the problem into the mail logs.
Not correct MAILFROM=""
Wrong. MAILFROM is a real crontab variable, but it only sets the envelope sender of the message cron generates. The mail is still sent.
Not correct SHELL=/bin/false
Wrong, and it breaks everything. SHELL selects the interpreter cron uses to run each command; pointing it at /bin/false means no command in the file executes.
Why
Cron mails anything a job writes to standard output or standard error to the crontab's owner, or to the address in MAILTO if that variable is set. An empty MAILTO suppresses the mail entirely; the alternative, and the more common one in practice, is to redirect per entry with `>/dev/null 2>&1`. Variable assignments in a crontab apply to the entries below them, so placement in the file matters.
Where this comes from
- Cited
- manual page crontab(5)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 107 and space the ones you get wrong.
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