easyMultiple Choice
XK0-006 Practice Question: A junior administrator is asked to automate the…
A junior administrator is asked to automate the backup of a configuration file every night at 11 PM. The script /usr/local/bin/backup.sh already exists. Which command should the administrator run to schedule this task?
⚠ Common exam trap
A common mix-up: candidates confuse `at` (for one-time tasks) with `cron` (for recurring tasks), or assume `systemctl start` can create a timer on the fly without a pre-existing timer unit file.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
echo "0 23 * * * /usr/local/bin/backup.sh" | crontab -
The `crontab -` command reads from standard input and installs the cron job. The line `0 23 * * * /usr/local/bin/backup.sh` specifies that the script should run at 23:00 (11 PM) every day, matching the requirement exactly. This is the standard method for scheduling recurring tasks in Linux using cron.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
systemctl start backup.timer
Why it's wrong here
systemctl start backup.timer only starts an existing systemd timer unit immediately; it neither creates the unit nor schedules a recurring 23:00 run. A systemd timer would be correct if a matching .timer and .service pair already existed and were enabled. Here the task requires a cron entry instead.
- ✗
at 23:00 /usr/local/bin/backup.sh
Why it's wrong here
at schedules a command to run once at a specified time, so it would execute the backup a single time at 23:00 rather than every night. It is tempting because the time syntax matches, but at is designed for one-off jobs. Recurring nightly execution requires a cron entry.
- ✓
echo "0 23 * * * /usr/local/bin/backup.sh" | crontab -
Why this is correct
Piping the schedule into `crontab -` installs it as the invoking user's crontab, and the five fields `0 23 * * *` fire the existing script daily at 23:00, satisfying the 11 PM requirement without editing files manually.
- ✗
nohup /usr/local/bin/backup.sh &
Why it's wrong here
nohup runs the script immediately in the background and detaches it from the terminal; it sets no schedule at all. It is tempting because it keeps a process running after logout, which suits long jobs started now. Recurring execution at 23:00 nightly needs a cron entry, not nohup.
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Related to this question
Learn chapter
System Backup and Recovery
Key term
crontab
Crontab is a time-based job scheduler in Unix-like operating systems that allows users to automate the execution of scripts or commands at specified intervals.
Key term
cron
Cron is a time-based job scheduler in Unix-like operating systems that automatically runs commands or scripts at specified dates and times.
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