Automatically Running Shell Scripts at System Startup on Linux

Running shell scripts automatically at system startup is a common requirement for many server and desktop applications. Whether it’s launching services, setting up environment configurations, or performing routine checks, automating these tasks can save time and reduce errors. This tutorial explores several methods to achieve this on Linux systems, focusing on creating executable scripts and leveraging existing tools like init.d, rc.local, chkconfig, and cron.

Understanding the Need for Startup Scripts

Startup scripts are used to automatically execute commands or launch services when a system boots up. This is especially useful for maintaining persistent processes such as web servers, database services, or custom applications. Automating these tasks ensures they are consistently executed without manual intervention.

Methods to Run Shell Scripts at Boot Time

1. Using /etc/init.d/ with chkconfig

For systems like Red Hat Linux and its derivatives, the /etc/init.d/ directory is used for init scripts. These scripts can be managed by the chkconfig utility to enable or disable them across different runlevels.

Steps:

1. Create the Script: Place your script in /etc/init.d/, ensuring it starts with a shebang (#!/bin/sh) and has executable permissions (chmod +x /path/to/script).

2. Define Run Levels: Include directives at the top of your script to specify run levels, such as:

   # chkconfig: 345 99 10
   

3. Manage with chkconfig: Use commands like chkconfig --add script_name and chkconfig --list script_name to manage its execution.

4. Control the Service: Start or stop your service using service script_name start/stop.

2. Using /etc/rc.local

The /etc/rc.local file is a traditional way to execute commands at the end of each multi-user runlevel boot process. This method is straightforward but requires that the script exits successfully.

Steps:

1. Edit /etc/rc.local: Add your command or script path, ensuring it ends with an ampersand (&) if you want to background the process:

   su - USER_FOOBAR -c /PATH/TO/MY_APP &
   

2. Ensure Execution: The file must be executable and end with exit 0.

3. Using cron with @reboot

The cron scheduler can also run scripts at boot time using the special @reboot directive.

Steps:

1. Edit Crontab: Open your crontab for editing with root privileges:

   sudo crontab -e
   

2. Add the Command: Add a line to execute your script at reboot:

   @reboot sh /home/user/test.sh
   

3. Save and Exit: Save changes using :wq or ZZ.

4. Test the Setup: Reboot the system to ensure the script runs as expected.

4. Using Systemd

Modern Linux distributions often use systemd, which provides a more flexible way to manage services with .service files.

Steps:

1. Create a Service File: Place your service file in /etc/systemd/system/. For example, myapp.service.

2. Define the Service:

   [Unit]
   Description=My Custom Application
   
   [Service]
   ExecStart=/path/to/start_my_app.sh
   
   [Install]
   WantedBy=multi-user.target
   

3. Enable the Service: Use systemctl to enable and start your service:

   sudo systemctl enable myapp.service
   sudo systemctl start myapp.service
   

Best Practices

• Absolute Paths: Always use absolute paths in scripts to avoid issues related to the working directory.
• Error Handling: Ensure your scripts handle errors gracefully, especially in startup contexts.
• Testing: Test your scripts manually before automating them at boot time.
• Security: Restrict permissions on startup scripts to prevent unauthorized modifications.

By following these methods and best practices, you can effectively manage and automate the execution of shell scripts at system startup on Linux systems.