How to Schedule a Cron Job on Linux: Step-by-Step

Cron lets you automate recurring tasks on Linux — from database backups to report generation to cache clearing. This guide walks through creating your first cron job and getting it to run reliably.

Prerequisites

Verify cron is running:

systemctl status cron        # Debian/Ubuntu (cronie or cron)
systemctl status crond       # CentOS/RHEL

If it’s not running:

sudo systemctl enable cron
sudo systemctl start cron

Step 1: Open your crontab for editing

crontab -e

This opens your user’s crontab file in the default editor (usually vi or nano). Each line is a scheduled job.

To use a different editor:

EDITOR=nano crontab -e

Or set it permanently:

export VISUAL=nano

Step 2: Write the cron expression

The format is five time fields followed by the command:

MINUTE HOUR DOM MONTH DOW COMMAND

Example — run a backup script every day at 2am:

0 2 * * * /home/ubuntu/backup.sh

Example — run a Python script every 15 minutes:

*/15 * * * * /usr/bin/python3 /home/ubuntu/scripts/sync.py

Step 3: Use full paths for everything

Cron runs with a minimal PATH (/usr/bin:/bin). Commands in your shell might not be found in cron. Use full paths:

# Check where a command lives
which python3
# /usr/bin/python3

which node
# /usr/local/bin/node

Then use those full paths in your crontab:

*/15 * * * * /usr/bin/python3 /home/ubuntu/scripts/sync.py >> /var/log/sync.log 2>&1

Or set PATH at the top of your crontab (before any job lines):

PATH=/usr/local/bin:/usr/bin:/bin
HOME=/home/ubuntu

*/15 * * * * python3 /home/ubuntu/scripts/sync.py >> /var/log/sync.log 2>&1

Step 4: Handle output

By default, cron emails output to the local user. To manage output:

# Suppress everything (silent)
0 2 * * * /home/ubuntu/backup.sh > /dev/null 2>&1

# Log to a file
0 2 * * * /home/ubuntu/backup.sh >> /var/log/backup.log 2>&1

# Log with timestamp
0 2 * * * echo "$(date) - starting backup" >> /var/log/backup.log && /home/ubuntu/backup.sh >> /var/log/backup.log 2>&1

Step 5: Save and verify

Save and exit the editor. Cron will automatically install the new crontab.

List your active cron jobs:

crontab -l

To see the cron daemon’s own logs:

# Debian/Ubuntu
grep CRON /var/log/syslog | tail -20

# CentOS/RHEL
grep CRON /var/log/cron | tail -20

Complete examples

Daily database backup at 3am:

0 3 * * * /usr/bin/pg_dump -U postgres mydb > /backups/mydb-$(date +\%Y\%m\%d).sql 2>> /var/log/backup.log

Note: % must be escaped as \% in crontab (unescaped % is interpreted as a newline).

Clear application cache every hour:

0 * * * * /usr/bin/php /var/www/html/artisan cache:clear >> /var/log/cache.log 2>&1

Check disk usage every 10 minutes and alert if over 80%:

*/10 * * * * /usr/local/bin/check-disk.sh

/usr/local/bin/check-disk.sh:

#!/bin/bash
USAGE=$(df / | tail -1 | awk '{print $5}' | tr -d '%')
if [ "$USAGE" -gt 80 ]; then
    echo "Disk usage at ${USAGE}%" | mail -s "Disk Alert" admin@example.com
fi

Run on startup:

@reboot sleep 30 && /home/ubuntu/start-worker.sh >> /var/log/worker.log 2>&1

The sleep 30 gives the system time to fully boot before the script starts.

Running as root

To schedule a system-level job (as root):

sudo crontab -e

Or add it to /etc/crontab, which has an extra user field:

# /etc/crontab format: MINUTE HOUR DOM MONTH DOW USER COMMAND
0 2 * * * root /usr/local/bin/backup.sh

Verifying it ran

Check the cron log after the scheduled time:

grep CRON /var/log/syslog | grep backup

Output looks like:

Apr 25 02:00:01 hostname CRON[12345]: (ubuntu) CMD (/home/ubuntu/backup.sh)

If you don’t see it, double-check the expression, confirm cron is running, and make sure your user has permission to run the command.

Build and validate cron expressions at crontab.io.