linuxexpert-practice-labs/labs/lpic-1/102-2-boot-manager/README.md

LPIC-1 102.2: Installing a boot manager

Changing GRUB's settings, regenerating grub.cfg, adding a custom menu entry, and using the GRUB menu and command line.

Before you start

Take a snapshot first: this lab changes the boot loader's configuration. The lab saves /etc/default/grub, /etc/default/grub.d/ and /etc/grub.d/40_custom; reset puts them back and regenerates grub.cfg. To see the GRUB menu you need the VM's console, not SSH.

Tasks

1. Change GRUB_TIMEOUT to 10, regenerate grub.cfg, and reboot to see it.
2. Add a kernel option at the menu with e for one boot, then check /proc/cmdline. Check it yourself: the option shows in /proc/cmdline for that boot only.
3. Copy an entry from grub.cfg into /etc/grub.d/40_custom, change its title, regenerate, and boot it. On AlmaLinux, grub.cfg has no entries to copy: write the entry from one of the files in /boot/loader/entries/ instead.
4. Open the GRUB command line with c and find your kernel with ls. Check it yourself: ls (hd0,gpt3)/ or similar lists a vmlinuz file.

Hints

• /etc/default/grub; on Ubuntu cloud images a file in /etc/default/grub.d/ sets GRUB_TIMEOUT again, after it, and GRUB_TIMEOUT_STYLE=hidden hides the menu.
• grub2-mkconfig -o /boot/grub2/grub.cfg on the RHEL family, update-grub on Debian and Ubuntu.
• A menuentry 'Title' { ... } block keeps its linux and initrd lines; on AlmaLinux they come from the linux, options and initrd lines of a BLS entry.
• grub2-reboot or grub-reboot with the title boots an entry once.