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Grub

If your system do not show grub menu, hold down SHIFT key on system start to show grub menu.

To press c to enter grub command line.

Show grub command prompt results paginated, run

set pager=1

ls command shows all available partitions. To see files in a partition, use ls (hd0,1)/

cat command can be used to display content of a file. Example: cat (hd0,1)/etc/issue

set command is used to set settings. If you don’t specify any value, it print out existing settings.

Setting kernel and booting up

grub> set root=(hd0,1)
grub> linux /boot/vmlinuz-3.13.0-29-generic root=/dev/sda1
grub> initrd /boot/initrd.img-3.13.0-29-generic
grub> boot

To generate grub.cfg on CentOS 7, run

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

Rebuild/Update grub.cfg

On Debian

root@hon-vpn:~# update-grub
Generating grub configuration file ...
Found background image: /usr/share/images/desktop-base/desktop-grub.png
Found linux image: /boot/vmlinuz-3.16.0-4-amd64
Found initrd image: /boot/initrd.img-3.16.0-4-amd64
done
root@hon-vpn:~#

View All Menu entry

CentOS/RHEL

grep menuentry /boot/grub2/grub.cfg

Debian/Ubuntu

grep menuentry /boot/grub/grub.cfg

Posted in CentOS