Modify The System Bootloader
General Information
Managing Grub2; the system boot loader.
Grub2 Structure
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
Grub2 Commands
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
- Edit grub2 variables
vim /etc/default/grub
- After making changes, re-generate the grub2 menu
grub2-mkconfig -o /boot/grub2/grub.cfg