Modify The System Bootloader

General Information

Managing Grub2; the system boot loader.

Grub2 files:

• /boot/grub2/grub.cfg ⇒ grub2 generated menu (do not edit directly)
• /etc/default/grub ⇒ grub2 variables (can be edited, then menus re-generated)
• /etc/grub.d/ ⇒ individual files used internally by grub2

Grub2 symlinks

• /etc/grub2.cfg ⇒ symlink to /boot/grub2/grub.cfg
• /etc/sysconfig/grub ⇒ symlink to /etc/default/grub

View the active kernel that is default for system boot

grub2-editenv list
 
saved_entry=CentOS Linux (3.10.0-327.3.1.el7.x86_64) 7 (Core)

View list of kernels displayed on grub menu

grep ^menuentry /boot/grub2/grub.cfg 
 
menuentry 'CentOS Linux (3.10.0-327.3.1.el7.x86_64) 7 (Core)' ...
menuentry 'CentOS Linux (3.10.0-327.el7.x86_64) 7 (Core)' ...
menuentry 'CentOS Linux (0-rescue-15bdd5425c924660bb6c9979dc071d56) 7 (Core)' ...

Set default kernel for grub system boot (permanent)

grub2-set-default 'CentOS Linux (3.10.0-327.3.1.el7.x86_64) 7 (Core)'

• Note: Copy/paste including the single quotes from the “grep ^menuentry” output

Changing Grub2 settings

1. Edit grub2 variables

   vim /etc/default/grub

2. After making changes, re-generate the grub2 menu

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