RebootIntoKernel

This simple Bash script automatises some common tasks usually performed when installing a customised or newer Linux Kernel by hand, to prevent the system from crashing when a Kernel Panic arises after rebooting into the new kernel.

Tested on

The script parses /boot/grub/grub.cfg in a naive way, so it has been only tested on Debian and Ubuntu systems. Some other GNU/Linux distros may as well work fine, but you should consider modifying the format_grub_meny_entry function accordingly.

Tested on the following GNU/Linux distros:

* Debian Wheezy.
* Debian Jessie.
* Debian Stretch.
* Ubuntu Trusty.
* Ubuntu Xenial.

Installation

git clone https://github.com/nonamed01/RebootIntoKernel.git

Usage

Get help:

./rk.sh -h

Get GRUB's menu entry for the current running kernel:

./rk.sh -g `uname -r`

Reboot automatically into kernel 4.19.2-amd64 and, if a Kernel Panic arises, reboot into the current running one after 5 seconds:

./rk.sh -t 5 -r -k 4.19.2-amd64

Use cases

After customising your running kernel, or after installing a newer one by hand with the distro-agnostic and old-fashioned make bzImage ; make modules ...,, once you have the vmlinuz and initrd files in /boot/, you can make use of this script to reboot into this new kernel and safely get back to the current running and stable one if an awful Kernel Panic is triggered.

Behind the scenes

This script performs the following tasks behind the scenes:

1. Adds (or updates) the panic variable to GRUB_CMDLINE_LINUX_DEFAULT in the /etc/defaults/grub.

2. Sets the variable GRUB_DEFAULT to saved in /etc/default/grub.

3. Sets the current running kernel as the saved one by calling grub-set-default. Then, it updates /boot/grub/grub.cfg by calling update-grub.

4. Sets the kernel to boot into the next reboot by calling grub-reboot.

5. Reboots the computer inmediately (if -r is given).

Demo

./rk.sh -t 20 -k 4.19.4
Timeout of 20 seconds for kernel panic set.
Default Running Kernel: Debian GNU/Linux, with Linux 4.9.0-8-amd64
Rebooting into the new installed kernel: Debian GNU/Linux, with Linux 4.19.4 ...
Do you want to reboot now [yn] ?
y
Connection to HOST closed by remote host.
Connection to HOST closed.