Use Cron to Automate Workflows and Scripts

Cron service on Ubuntu

Check if cron is installed

cron --version

Install cron (if missing)

sudo apt update
sudo apt install cron

Start and enable cron

sudo systemctl start cron
sudo systemctl enable cron

Check status

sudo systemctl status cron

Crontab basics

Each user has their own cron table (crontab).

Open your crontab

crontab -e

Writing .sh scripts for cron

Create a script

mkdir -p ~/cron-scripts
nano ~/cron-scripts/backup.sh

Example script

#!/bin/bash

echo "Backup started at $(date)"
tar -czf /home/ali/backups/home_$(date +%F).tar.gz /home/ali/data
echo "Backup completed"

Make it executable

chmod +x ~/cron-scripts/backup.sh

Test manually (IMPORTANT)

~/cron-scripts/backup.sh

Cron should never be the first place you test a script.

Running scripts using crontab

Edit crontab:

crontab -e

Add:

0 1 * * * /home/ali/cron-scripts/backup.sh

Cron will:

• Run as your user

• Not load your .bashrc or .profile

Running MULTIPLE .sh scripts in cron

You have 2 correct ways to do this.

Option 1: Multiple cron entries (recommended)

0 1 * * * /home/ali/cron-scripts/backup.sh
15 1 * * * /home/ali/cron-scripts/cleanup.sh
30 1 * * * /home/ali/cron-scripts/report.sh

Option 2: One master script (BEST for pipelines)

Create a wrapper script:

nano ~/cron-scripts/run_all.sh

#!/bin/bash

/home/ali/cron-scripts/backup.sh
/home/ali/cron-scripts/cleanup.sh
/home/ali/cron-scripts/report.sh

chmod +x ~/cron-scripts/run_all.sh

Cron entry:

0 1 * * * /home/ali/cron-scripts/run_all.sh

Environment & PATH issues

This may fail:

python script.py

Use absolute paths:

/usr/bin/python3 /home/ali/scripts/script.py

Check path:

which python3
which bash

Set PATH in crontab (optional)

PATH=/usr/local/bin:/usr/bin:/bin

Logging cron output

By default, cron does not show output.

Redirect output

0 1 * * * /home/ali/script.sh >> /home/ali/cron.log 2>&1

Check logs

cat ~/cron.log

Debugging cron jobs

List your cron jobs

crontab -l

Check system cron logs

grep CRON /var/log/syslog

Test with simple command

* * * * * echo "cron works" >> /tmp/cron_test.log