/var/run/reboot-required.

The file /var/run/reboot-required on Debian-based distributions like Debian, Ubuntu, and Linux Mint indicates that a reboot is necessary after specific updates, typically when critical components such as the kernel or system libraries (e.g., glibc) have been upgraded. This file is automatically generated by the package management system (e.g., apt) during these updates, usually created by post-installation scripts for packages that need a reboot to complete their installation, such as a new kernel.

To ensure that your system is ready for optimal performance and security, it's important to check for the presence of this file after applying updates. This simple step can help you determine if a reboot is necessary to apply the latest changes effectively.

Check if a Reboot is Required

By testing if the file exists.

$ [ -f /var/run/reboot-required ] && echo "Reboot required"

If the file exists, the system will output "Reboot required".

Here's a breakdown of the above command line (CLI):

a. [: This is a synonym for the test command in shell scripting. It checks the condition specified inside the brackets.
-f /var/run/reboot-required: This is the condition being tested.

b. -f: This flag checks if the specified path refers to a regular file.

c. /var/run/reboot-required: This is the path being checked. If this file exists and is a regular file, the condition returns true.

d. &&: This is a logical AND operator. It allows you to execute the command that follows it only if the preceding command (the test in this case) is true.

e. echo "Reboot required": If the condition is true (meaning the file exists), this command will execute, outputting the text "Reboot required" to the terminal.

Use the cat command to display any message within the file.

$ cat /var/run/reboot-required

This will usually display something like:

*** System restart required ***

After you reboot the system, the /var/run/reboot-required file is automatically removed. There's no need for manual deletion, as the system handles this process for you, ensuring a clean and efficient update experience.
System administrators should check for its presence after running updates, especially kernel or core system library updates, to ensure the system is properly rebooted for all changes to take effect.

We hope you found these insights useful!