A Guide to Using the kexec Command (with examples)

Load a new kernel

To load a new kernel using the kexec command, you can use the following code:

kexec -l path/to/kernel --initrd=path/to/initrd --command-line=arguments

• Motivation: This use case is useful when you want to switch to a new kernel without rebooting the system. It can be handy during kernel development or testing.
• Explanation:
  • path/to/kernel: Specify the path to the new kernel image that you want to load.
  • --initrd=path/to/initrd: Specify the path to the initial ramdisk (initrd) image that you want to provide to the new kernel.
  • --command-line=arguments: Specify additional command-line arguments for the new kernel (optional).
• Example Output: None. This command prepares the system to boot into the new kernel.

Load a new kernel with current boot parameters

To load a new kernel using the current boot parameters, you can use the following code:

kexec -l path/to/kernel --initrd=path/to/initrd --reuse-cmdline

• Motivation: This use case is helpful when you want to load a new kernel using the same command-line arguments as the currently running kernel. It saves you the effort of manually specifying arguments.
• Explanation:
  • path/to/kernel: Specify the path to the new kernel image that you want to load.
  • --initrd=path/to/initrd: Specify the path to the initial ramdisk (initrd) image that you want to provide to the new kernel.
  • --reuse-cmdline: Reuse the command-line arguments from the currently running kernel.
• Example Output: None. This command prepares the system to boot into the new kernel using the same command-line arguments.

Execute a currently loaded kernel

To execute the currently loaded kernel, you can use the following code:

kexec -e

• Motivation: This use case is useful when you have loaded a new kernel using the kexec command and want to immediately execute it without rebooting the system.
• Explanation: None.
• Example Output: None. The currently loaded kernel starts executing.

Unload current kexec target kernel

To unload the currently loaded kexec target kernel, you can use the following code:

kexec -u

• Motivation: This use case is beneficial when you want to unload the previously loaded kernel without rebooting the system, freeing up system resources.
• Explanation: None.
• Example Output: None. The currently loaded kexec target kernel is unloaded.

Note: The kexec command has several other use cases which are not covered in the examples above. Please refer to the official documentation for more information.