How to create RC local?

Creating an rc.local file involves a few straightforward steps to enable a legacy service that allows you to run custom commands at system boot-up on Linux distributions primarily using systemd.

rc.local is a script executed once at the end of the traditional boot sequence, offering a simple way to automate tasks that need to run before users log in. While systemd is the modern init system, rc.local functionality can still be enabled for specific use cases.

How to Create and Enable RC Local

Here's a step-by-step guide to create and enable rc.local on your system:

Step 1: Check the Status of the rc-local Service

Before creating the file, you can check if the rc-local service unit is already present and its current status. This helps in understanding if the system is configured to handle rc.local scripts.

sudo systemctl status rc-local

If the service is not found or is inactive, you'll proceed to create the necessary files and enable it.

Step 2: Create the rc.local Script File

First, you need to create the rc.local script itself in the /etc/ directory. This file will contain all the commands you want to execute at boot.

1. Open a text editor with root privileges to create the file. Using nano is a common choice for its simplicity:

   sudo nano /etc/rc.local

2. Add the necessary content to the file. A basic rc.local script should always start with a shebang line to specify the interpreter (#!/bin/bash) and end with exit 0 to indicate successful execution.
   Here's an example of what to put in your /etc/rc.local file:

   #!/bin/bash
   
   # Add your custom commands here that you want to execute at boot.
   # For example, to print a message to the system log:
   # echo "rc.local script executed!" >> /var/log/syslog
   
   # Or to start a specific service/application:
   # /opt/my_application/start.sh
   
   # Make sure to include the full path to any commands or scripts you run.
   
   exit 0

   • #!/bin/bash: This line ensures the script is executed by bash.
   • exit 0: This line is crucial. It tells the system that the script executed successfully. Without it, the rc-local service might report an error.

3. Save and close the file. In nano, press Ctrl+O to write out, then Enter to confirm the filename, and Ctrl+X to exit.

Step 3: Make the rc.local Script Executable

The system needs permission to execute the script. You must grant executable permissions to the /etc/rc.local file:

sudo chmod +x /etc/rc.local

This command makes the script executable for all users, which is necessary for the system to run it.

Step 4: Enable the rc-local Service on System Boot

For systemd to recognize and run your rc.local script at every boot, you need to enable the rc-local service. This will ensure the service starts automatically.

sudo systemctl enable rc-local

If rc-local.service unit file doesn't exist, systemd might automatically create a symlink to /etc/rc.local or you might need to manually create a systemd service unit to wrap the rc.local functionality if your distribution doesn't provide one by default. Modern distributions often include a default rc-local.service unit that simply executes /etc/rc.local if it exists and is executable.

You can then start the service immediately without rebooting to test it:

sudo systemctl start rc-local

Verify its status again:

sudo systemctl status rc-local

It should now show as active (exited) or active (running) depending on your distribution's setup and if your script has long-running processes.

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Understanding the rc-local.service Unit

On systemd based systems, the execution of /etc/rc.local is managed by a systemd service unit, typically named rc-local.service. This service unit ensures that the rc.local script is run at the appropriate stage during boot. If your distribution does not have this unit file by default, you might need to create one (e.g., /etc/systemd/system/rc-local.service). However, most major distributions like Ubuntu and Debian provide it, often as a symlink to /lib/systemd/system/rc-local.service or similar.

A typical rc-local.service unit file looks like this:

[Unit]
Description=/etc/rc.local compatibility
ConditionPathExists=/etc/rc.local

[Service]
Type=forking
ExecStart=/etc/rc.local start
TimeoutSec=0
StandardOutput=tty
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

This unit ensures that if /etc/rc.local exists, it will be executed before multi-user.target is reached (meaning, before most services are fully up and running).

Best Practices and Considerations

• Full Paths: Always use absolute (full) paths for commands and files within your rc.local script (e.g., /usr/bin/python instead of python, /var/www/html/myscript.sh instead of myscript.sh). The environment rc.local runs in might not have the same PATH variable as your interactive shell.
• Logging: Redirect output from your commands to a log file (>> /var/log/my_custom_log.log 2>&1) to help with debugging.
• Error Handling: Be mindful of commands that might fail. rc.local runs early in the boot process, and some services or network connectivity might not be fully available yet.
• Alternatives: For more complex or critical services, systemd unit files are the recommended modern approach. They offer better control over dependencies, logging, and error handling. Learn more about systemd service units.
• Security: Only add commands from trusted sources to rc.local, as it runs with root privileges.

Summary of Commands

Here's a quick reference table for the commands involved:

Command	Purpose
sudo systemctl status rc-local	Check if the rc-local service is active.
sudo nano /etc/rc.local	Create or edit the rc.local script file.
sudo chmod +x /etc/rc.local	Make the rc.local script executable.
sudo systemctl enable rc-local	Enable rc-local to start at boot time.
sudo systemctl start rc-local	Start the rc-local service immediately.
sudo systemctl disable rc-local	Disable rc-local from starting at boot.

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By following these steps, you can effectively create and utilize rc.local to execute custom scripts and commands at system startup.