Create a Cron Job

🎯 Objective

Learn how to schedule automated tasks in Linux using cron jobs.

🧠 What is a Cron Job?

A cron job is a scheduled task that runs automatically at a specific time or interval.

👉 Used for:

⚙️ Cron Structure (Very Important)

A cron expression has 5 time fields + command:

* * * * * command_to_run
│ │ │ │ │
│ │ │ │ └── Day of Week (0-7) (Sun=0 or7)
│ │ │ └──── Month (1-12)
│ │ └────── Day of Month (1-31)
│ └──────── Hour (0-23)
└────────── Minute (0-59)

📌 Common Examples

🛠️ Step 1: Open Crontab

crontab-e

👉 This opens your cron configuration file.

🛠️ Step 2: Add a Cron Job

Example:

* * * * *echo"Hello Cron" >> /tmp/cron.log

👉 Runs every minute and writes to a log file.

🛠️ Step 3: Save & Exit

🔍 Step 4: Verify Cron Jobs

crontab-l

👉 Lists all scheduled jobs.

🧪 Step 5: Check Output

cat /tmp/cron.log

🔁 Real-World Example (Laravel)

Run Laravel scheduler every minute:

* * * * *cd /var/www/project && php artisan schedule:run >> /dev/null2>&1

🧠 Explanation:

🚀 Advanced Example

Run a script every day at 2 AM:

02 * * * /usr/bin/bash /home/user/backup.sh

⚠️ Important Tips

1. Use Full Paths

Cron doesn’t load your environment like terminal:

/usr/bin/php   ✅
php            ❌

2. Environment Variables Issue

Cron runs in a limited environment.

👉 Fix:

3. Logging is Important

* * * * * command >> /var/log/myjob.log2>&1

4. Check Cron Service

On systems using systemd:

sudo systemctl status cron
# or
sudo systemctl status crond

Start if needed:

sudo systemctlstart cron

🧩 Common Use Cases

❌ Common Mistakes

📌 Summary