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0 2 * * * /absolute/path/to/verify.sh >> /absolute/path/to/verify.log 2>&1Replace /absolute/path/to/verify.sh with the command or script that checks the item you want verified, and replace the log path with a writable location.
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What the daily cron line means
A standard cron entry has five time fields followed by the command: minute, hour, day of month, month, and day of week. In 0 2 * * *, the zero minute and hour 2 mean 02:00; the asterisks mean every day of the month, every month, and every day of the week. The time is based on the host’s cron and timezone configuration, so check the machine’s timezone before choosing an hour. See the Debian bookworm crontab(5) manual and Cronie crontab(5) manual for implementation-specific details.
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The redirection >> /absolute/path/to/verify.log 2>&1 appends standard output to the log and sends standard error to the same destination. The Debian bookworm manual gives a similar example, 5 0 * * * $HOME/bin/daily.job >> $HOME/tmp/out 2>&1, which it describes as running five minutes after midnight each day. Cron may also mail job output when mail is configured, and some implementations can send output to syslog; do not assume either is set up on your host. See cron(8).
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Set up and check the job
- Identify the real check. Decide which command performs the verification and what success and failure look like. The placeholder
verify.shis not itself a verification check. - Run it manually under the account that should own the job. Confirm it behaves as expected, and use absolute paths for the script and any files it needs. A user crontab runs jobs as its owner, so choose the account with the necessary permissions.
- Edit that account’s crontab. Run
crontab -e, add the daily line, and save it. Choose a suitable hour based on the host’s timezone and workload. - Review the saved entry. Run
crontab -land confirm the schedule, command, and log path are correct. - Verify the first scheduled run. After the selected time, inspect the log for the check’s expected result. If no output appears, check the cron service’s logs or journal using the method appropriate to that Linux distribution.
In a system-wide crontab, the format commonly includes a username field between the time fields and command; do not copy a user-crontab line into a system-wide file without checking that file’s required format. Cron implementation, service names, and diagnostic locations vary by distribution.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Choose a schedule with timezone and downtime in mind
Cron’s behavior around daylight-saving clock changes and timezone selection depends on the implementation. Cronie documents that jobs scheduled during a skipped local time may not run, while jobs in a repeated local time can run twice. Debian’s systemd-cron documentation describes limitations in per-user timezone behavior. If running exactly once across clock changes matters, consult the manual for the cron implementation installed on the target host rather than assuming all systems interpret local time identically.
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A cron schedule by itself does not establish that a job will catch up after a machine is powered off at its scheduled time. If missed-run handling or explicit timer/service status is important, consider whether a systemd timer fits the host. Oracle’s Oracle Linux 9 guide to automating system tasks documents timers as an alternative and shows systemctl list-unit-files --type=timer to list timer units and systemctl cat name.timer to inspect a unit. Catch-up behavior depends on the timer’s configuration; verify it rather than assuming it is enabled.
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