[Grub2] Change the default boot kernel #grub #linux

grub2

1. Generate the up to date grub configuration

$ grub2-mkconfig -o /boot/grub2/grub.cfg


2. Get the boot sequence of the kernels in the grub configuration

$ grep '^menuentry' /boot/grub2/grub.cfg

This will show the sequence in which the kernels are displayed

menuentry 'Oracle Linux Server (4.1.12-61.1.6.el7uek.x86_64 with Unbreakable Enterprise Kernel) 7.2' --class ol --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-4.1.12-61.1.6.el7uek.x86_64-advanced-7e585ba2-aa3d-4b3f-b447-b0fe12a1f076' {
menuentry 'Oracle Linux Server (3.10.0-327.el7.x86_64 with Linux) 7.2' --class ol --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-3.10.0-327.el7.x86_64-advanced-7e585ba2-aa3d-4b3f-b447-b0fe12a1f076' {
menuentry 'Oracle Linux Server (0-rescue-ef6d98a7dc3c439a98df9c2ceb1b7065 with Linux) 7.2' --class ol --class gnu-linux --class gnu --class os --unrestricted $menuentry_id_option 'gnulinux-0-rescue-ef6d98a7dc3c439a98df9c2ceb1b7065-advanced-7e585ba2-aa3d-4b3f-b447-b0fe12a1f076' {


3. The sequence is listed with index 0 being first. So for example from the above list, if you wanted Kernel 3.10 to be the default
then the index will be 1.

4. Set the default boot kernel using the index

$ grub2-set-default 1


Alternately, you could also use the full name of the kernel in the above command