Which user crontab line runs /usr/local/bin/backup.sh at 03:30 every day?
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
Not correct 3 30 * * * /usr/local/bin/backup.sh
Wrong: the fields are reversed. This reads as minute 3 of hour 30, and hour 30 does not exist, so cron rejects the line.
Correct 30 3 * * * /usr/local/bin/backup.sh
Correct. Minute 30, hour 3, every day of month, every month, every day of week.
Not correct * 3:30 * * * /usr/local/bin/backup.sh
Wrong. Crontab has no clock-time syntax; each of the five fields is a separate numeric field and a colon is not valid in any of them.
Not correct 30 3 * * * root /usr/local/bin/backup.sh
Wrong in a USER crontab. The extra user field belongs only in /etc/crontab and in files under /etc/cron.d. Here cron would try to run a command literally named root, and the schedule would fail with an error mail.
Why
The five fields are, in order: minute (0-59), hour (0-23), day of month (1-31), month (1-12 or names), day of week (0-7, where both 0 and 7 mean Sunday). The command follows. When both day-of-month and day-of-week are restricted, cron runs the job if EITHER matches, which surprises people who expect an AND.
Where this comes from
- Cited
- LPI exam objective 107.2
- What it says
- Manage cron jobs and understand the crontab time specification.
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.
More questions on this objective
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