Verify completion of scheduled jobs

Ensuring your scheduled tasks run as expected is critical for system reliability. CentOS Stream 8 provides three primary schedulers—cron, anacron, and at—all of which log their execution events by default. In this guide, you’ll learn how to confirm job completion, capture outputs, and troubleshoot using system logs and the journal.

Table of Contents

1. Verifying cron Jobs
2. Inspecting the System-wide crontab
3. Verifying anacron Jobs
4. Capturing anacron Job Output
5. Verifying at-scheduled Jobs
6. Log Files Reference
7. References

1. Verifying cron Jobs

1. Open your user crontab for editing:

   crontab -e
   

2. Add two simple echo commands to run every minute:

   * * * * * /bin/echo "Just testing cron"
   * * * * * /bin/echo "Just testing cron again"
   

3. Save and exit. Wait at least one minute, then review the cron log:

   sudo cat /var/log/cron
   

4. You should see entries similar to:

   Mar 24 01:05:01 LFCS-CentOS CROND[9203]: (aaron) CMD (/bin/echo "Just testing cron again")
   Mar 24 01:05:01 LFCS-CentOS CROND[9204]: (aaron) CMD (/bin/echo "Just testing cron")
   

5. To filter only executed commands, use grep:

   sudo grep CMD /var/log/cron
   

2. Inspecting the System-wide crontab

View the system-wide crontab to understand global settings and syntax:

cat /etc/crontab

Example excerpt:

SHELL=/bin/bash
PATH=/sbin:/bin:/usr/sbin:/usr/bin
MAILTO=root

# ┌───────── minute (0 - 59)
# │ ┌─────── hour (0 - 23)
# │ │ ┌───── day of month (1 - 31)
# │ │ │ ┌─── month (1 - 12)
# │ │ │ │ ┌─ day of week (0 - 6)
# * * * * * user-name  command to be executed

• MAILTO controls where cron sends job output via email.
• Global environment variables apply to all entries.

3. Verifying anacron Jobs

Anacron ensures periodic jobs run even if the system was powered off when they were scheduled.

1. Edit the anacrontab:

   sudo vi /etc/anacrontab
   

2. Example /etc/anacrontab with a custom test_job:

   SHELL=/bin/sh
   PATH=/sbin:/bin:/usr/sbin:/usr/bin
   MAILTO=root
   RANDOM_DELAY=45
   START_HOURS_RANGE=3-22
   
   #period delay  job-identifier  command
   1       5      cron.daily      nice run-parts /etc/cron.daily
   7      25      cron.weekly     nice run-parts /etc/cron.weekly
   @monthly 45    cron.monthly    nice run-parts /etc/cron.monthly
   1      10      test_job        /bin/echo "Testing anacron"
   

3. Force anacron to execute all jobs immediately:

   sudo anacron -n
   

4. Review anacron entries in the cron log:

   sudo grep anacron /var/log/cron
   

   Example output:

   Mar 24 01:01:01 LFCS-CentOS anacron[8903]: Anacron started on 2022-03-24
   Mar 24 01:01:01 LFCS-CentOS anacron[8903]: Will run job `test_job` in 12 min.
   Mar 24 01:13:01 LFCS-CentOS anacron[8903]: Job `test_job` started
   Mar 24 01:13:01 LFCS-CentOS anacron[8903]: Job `test_job` terminated (produced output)
   

5. To view only your custom job entries:

   sudo grep test_job /var/log/cron
   

4. Capturing anacron Job Output

By default, anacron logs only “produced output.” To capture the full output in the system journal:

1. Modify the test_job command to use systemd-cat:

   1   10  test_job  /bin/echo "Testing anacron" | systemd-cat --identifier=test_job
   

2. Save changes and rerun jobs:

   sudo anacron -n -f
   

3. Query the journal for your job identifier:

   journalctl -e | grep test_job
   

   You’ll see both the start/stop messages and the actual command output:

   Mar 24 01:13:01 LFCS-CentOS test_job[8903]: Testing anacron
   

5. Verifying at-scheduled Jobs

The at daemon handles one-off scheduled tasks.

1. Schedule a job to run in one minute:

   at 'now + 1 minute'
   warning: commands will be executed using /bin/sh
   at> echo "My at job produced this output" | systemd-cat --identifier=at_scheduled_backup
   at> <EOT>
   job 5 at Thu Mar 24 01:22:00 2022
   

2. Confirm the atd daemon started your job:

   sudo grep atd /var/log/cron
   

   Example:

   Mar 24 01:22:00 LFCS-CentOS atd[10028]: Starting job 5 (a0000501la3224z) for user 'aaron' (1000)
   

3. View the job output in the journal:

   journalctl | grep at_scheduled_backup
   

   Mar 24 01:22:00 LFCS-CentOS at_scheduled_backup[10028]: My at job produced this output
   

4. On systems without journald, check /var/log/messages or /var/log/syslog for at entries.

Log Files Reference

References

• cron Manual (man cron)
• anacron Documentation
• at Manual (man at)
• systemd-cat
• journalctl