Automating Linux Scripts with Crontab

As I continue my cloud engineering journey at AltSchool Africa, I have been thinking more about automation.

One question I had was simple:

After writing a script, do I always have to run it manually with ./memory_usage.sh?

For example, if I write a script to check memory usage, do I need to manually execute it every time?

The answer I discovered is no.

This is where crontab becomes very useful.

What is crontab?

crontab is a task scheduler in Unix and Linux systems. It allows you to automate repetitive tasks by setting them to run at specific times or intervals.

Instead of manually running a script every hour, every day, or every month, you can tell the system to run it automatically.

Crontab is useful for things like:

Running backup scripts
Cleaning up old log files
Sending automated reports
Running monitoring scripts
Performing system maintenance
Running custom Bash scripts
Scheduling database maintenance
Automating web application tasks

How crontab works

A normal crontab schedule has five time fields followed by the command you want to run:

* * * * * command

Each asterisk represents a different part of the schedule:

* * * * *
| | | | |
| | | | └── Day of the week: 0 - 7, where 0 and 7 mean Sunday
| | | └──── Month: 1 - 12
| | └────── Day of the month: 1 - 31
| └──────── Hour: 0 - 23
└────────── Minute: 0 - 59

Example

Suppose I have a script located here:

/home/kaybee/memory_usage.sh

If I want the script to run on the 15th day of every month at exactly midnight, I can write:

0 0 15 * * /home/kaybee/memory_usage.sh

This means:

0     → minute 0
0     → hour 0, midnight
15    → 15th day of the month
*     → every month
*     → any day of the week

So the script will run once every month on the 15th.

Crontab shortcuts

Crontab also has special shortcuts that make scheduling easier:

@hourly   /home/kaybee/memory_usage.sh
@daily    /home/kaybee/memory_usage.sh
@weekly   /home/kaybee/memory_usage.sh
@monthly  /home/kaybee/memory_usage.sh
@yearly   /home/kaybee/memory_usage.sh
@reboot   /home/kaybee/memory_usage.sh

These mean:

@hourly runs once every hour
@daily or @midnight runs once every day at midnight
@weekly runs once every week
@monthly runs once every month
@yearly or @annually runs once every year
@reboot runs when the system starts

Why this matters in cloud engineering

Automation is an important part of cloud engineering.

In cloud environments, engineers often need to manage servers, monitor systems, clean logs, run backups, and schedule maintenance tasks. Doing these things manually every time is not efficient.

Tools like crontab help improve consistency and reliability because tasks can run automatically at the right time.

For me, learning crontab helped me understand that cloud engineering is not just about launching servers. It is also about managing systems properly and making them more efficient through automation.

What I learned

The biggest lesson for me was this:

If a task is repetitive, it is a good candidate for automation.

Instead of manually running scripts again and again, I can schedule them and let the system handle the work.

As I continue learning at AltSchool Africa, I am gaining more hands-on experience with Linux, Bash scripting, and automation tools like crontab. These are small steps, but they are important foundations for becoming a better cloud engineer.