Scheduling Tasks with cron

By the end of this lesson you'll be able to schedule commands to run automatically — every night, every 15 minutes, or once at startup — using cron's five schedule fields, special shortcuts, and a crontab that actually runs reliably.

Learn Scheduling Tasks with cron in our free Command Line course — an interactive lesson with worked examples, a practice exercise and a quick reference.

Part of the free Cli course at LearnCodingFast — hands-on lessons with examples you run in your browser, plus practice exercises and a quick quiz.

1. The crontab: -e, -l and -r

Your personal schedule lives in a file called your crontab , but you never open that file by hand — you manage it with three commands. crontab -e edits it (this is how you add jobs), crontab -l lists it, and crontab -r removes it. Be careful: crontab -r deletes your entire crontab with no confirmation, and it's one key away from -e — a classic footgun. Back up first with crontab -l > backup.txt .

2. The Five Schedule Fields

Every cron line is five time fields followed by the command. The order, left to right, is always: minute (0-59), hour (0-23), day-of-month (1-31), month (1-12), and day-of-week (0-7, where both 0 and 7 mean Sunday). So 30 2 * * * means minute 30, hour 2, any day, any month, any weekday — i.e. 02:30 every day .

3. Field Syntax: *, Steps, Ranges & Lists

Each field accepts four building blocks. * means every value. */n is a step — */5 in the minute field means every 5 minutes. a-b is a range — 1-5 in day-of-week is Monday through Friday. And a,b,c is a list — 1,15,30 . Combine them to express almost any schedule you need.

4. Special Shortcuts: @daily, @reboot & Friends

For common schedules, cron offers shortcuts that replace all five fields. @reboot runs a job once when the system boots; @hourly , @daily , @weekly , @monthly , and @yearly are readable aliases — for example @daily is exactly 0 0 * * * . You still add the command after the shortcut.

5. Output, Email & Logging

By default, cron emails whatever a job prints (stdout and stderr) to the local user. Put MAILTO="you@example.com" at the top of the crontab to choose the recipient, or MAILTO="" to switch that mail off. More commonly, people send output to a log file by appending >> /var/log/task.log 2>&1 — where 2>&1 routes errors into the same log so nothing is lost.

6. cron's Minimal Environment (use absolute paths!)

This is the single most common reason a cron job "works in my shell but not in cron." cron runs with a minimal environment : a sparse PATH (often just /usr/bin:/bin ) and none of your ~/.bashrc or login settings. So always use absolute paths to your commands and scripts — /usr/bin/python3 /home/user/app/job.py — or set PATH= at the top of the crontab. As a fast contrast: at runs a command once at a future time, and systemd timers are a modern alternative on systemd-based Linux.

Fill in the two blanks marked ___ using the # 👉 hints, then read the line back left to right and check it matches the Output panel.

Two blanks again: pick the step syntax for "every 15 minutes," and the redirect that appends output to a log. Then check the Output panel.

No blanks this time — just a brief and an outline. Build the full cron line that runs a report script at 8:00 AM on weekdays and logs its output. Plan each field in order, use the absolute path, and check your line against the target in the comments.

Practice quiz

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