grub

CentOS 7 Grub 2
grubby
OVH CentOS 7 server grub rescue prompt

RHEL Based – AlmaLinux, CentOS, RockeyLinux, Oracle Linux

Regenerate grub config

grub2-mkconfig -o /boot/grub2/grub.cfg
grub2-mkconfig -o /boot/efi/EFI/centos/grub.cfg
grub2-mkconfig -o /boot/efi/EFI/almalinux/grub.cfg

grub config on RHEL

/etc/default/grub

To install Grub, run

/sbin/grub2-install /dev/sda

To see all available kernels

awk -F\' '$1=="menuentry " {print i++ " =  "$2}' /etc/grub2.cfg

If all kernels not showing, edit

vi /etc/default/grub

Add

GRUB_DISABLE_SUBMENU=true
GRUB_DEFAULT=saved

Rebuild grub

grub2-mkconfig -o /etc/grub2.cfg

To set the default Kernel

grub2-set-default 0

To view current default kernel

[root@web ~]# grubby --default-kernel
/boot/vmlinuz-5.14.0-687.39.1.el9_8.x86_64
[root@web ~]# 

To see the current Kernel

grub2-editenv list

Reinstall kernel and set it to default

yum reinstall kernel
grub2-set-default 0
grubby --set-default 0

Ubuntu

sudo update-grub
/usr/sbin/grub-mkconfig -o /boot/grub/grub.cfg