Setting a Default Boot Kernel

It can get annoying choosing the real-time kernel from the submenu every time you boot your computer, especially if you miss the timing and it boots generic Linux.

By default, the GRUB bootloader sorts your installed kernels in descending version based on the kernel version number, and boots from the first one. You can save yourself some frustration by changing GRUB to boot from the real-time kernel by default.

Note: This is only for convenience. It has no effect on real-time performance or the functioning of RTXI.

While it is possible to specify a specific kernel, it is much easier to tell GRUB to use the kernel used last time. To make GRUB do this, open /etc/default/grub as root and make the following edits:

1. Change GRUB_DEFAULT=0 to GRUB_DEFAULT=saved.
2. Add a new line that says GRUB_SAVEDEFAULT=true.

Save your edits (again, you need to be root), and update GRUB by running:

$ sudo update-grub

From now on, GRUB will boot the last-used kernel by default. If you want to choose a different one, select it manually.

Note: If you have a LUKS-encrypted volume or otherwise encrypt your boot partition, this will fail. You will have to manually change the GRUB_DEFAULT options to something like "1>2", for example, which will make GRUB boot the kernel listed as the third option in the submenu opened on the second line of the main menu.