This is an original planning guide. It is not a vendor manual, an official standard, or legal advice. Example addresses use documentation ranges. Review every command before you paste it.
What this hour is for
A crontab line is minute, hour, day of month, month, and day of week. A star means every. A range and a step are still one schedule. The explainer turns the expression you typed into a sentence. The next-run calculator lists the following times. Neither tool installs a crontab.
Day of month and day of week together surprise people. If both are restricted, cron may run when either matches. Read the sentence the explainer gives you. Do not guess.
The user whose crontab it is matters. A job in root's crontab is a different decision from a job in an application user. The command's PATH is not your login PATH. That belongs in the troubleshooting page if the job does not run.
Do not hide a job. The schedule is a sentence a second person can read. 192.0.2.10/24 and example.com are documentation. They stay in the note.
The change you can finish
Apply nothing while you are writing the note. When the lab window opens, it is one change on the host named in the ticket. Read the draft, then the host, then decide.
Rollback is the file, the package version, or the snapshot you saved first. You do not invent a rollback after the only copy is gone.
- Write the schedule in a sentence.
- Draft the five fields.
- Read the explainer sentence.
- List the next runs.
- Name the user.
- Do not install the line during the reading.
Mistakes that outlive the command
Cron Syntax Guide goes wrong in a small set of ways. The list is here so the ticket can forbid them before the window.
- Six fields copied from a different scheduler.
- Day of month and day of week both set without reading the sentence.
- A job hidden in a system crontab.
- The calculator treated as an install.
Decisions to write down
One decision for Cron Syntax Guide: Five fields match the sentence. The next runs look like the sentence. The user is named. The line is not installed yet. And a second person can read the schedule.
Checks before you call it done
Confirm this before you call the change done: The sentence is written. The five fields match. The next run was listed. The user is named. And no crontab was edited. If one of those fails, stop.
# minute hour day month weekday
# Read the sentence before you install.
# The tools do not edit a crontab.Before you leave the host
Cron Syntax Guide ends when the hostname in the prompt matches the hostname in the ticket. If it does not, you are on the wrong host. Stop. A command that succeeded on the wrong host is not progress.
The draft stays a draft until a person has read the names in it. A generator does not log into the host and does not know which disk is empty. You delete a line that names a host, a path, or an account you did not write down.
192.0.2.10/24, gateway 192.0.2.1, 198.51.100.0/24, 203.0.113.0/24, and 2001:db8::/32 are documentation. example.com is a documentation name. They belong in the note. They are not values you leave on a host because a draft included them.
prompt-for-this is a reminder that a secret is missing. It is not a password, a key, or a token you save in the ticket or in git. The real secret stays in the password store.
One change is the window. If two things move and the result is wrong, you will not know which one did it. The next change waits for its own page.
If the same step fails twice, stop for the day. The failure is the result. Adding a forum command beside a half-applied change produces a host nobody can rebuild. Restore the copy you took first.
A second person reads the hostname and the change aloud. If they cannot find them in the ticket, the note is not done. Silence is not agreement. Then leave the host alone.
This page is a planning guide. It is not a vendor manual, not an official standard, and not permission to touch a host you do not administer. You do not disable a firewall, AppArmor, or SELinux to make a check pass.
Tools for this guide
These tools run in the browser on this site. They do not log into your machines.
Related pillar guides
More in this cluster
The pillar for this page, and the next published pages filed with it.