When booting a system, you can access the GRUB menu by pressing a key before the timeout expires. GRUB displays the title entries from the /boot/grub/grub.conf file, and highlights the default entry. You can use the up and down arrow keys to choose a different entry and press Enter to boot it.

If you have set a GRUB password, you must press P and enter the valid password to be able to edit the titles or change kernel boot parameters. To edit any of the root, kernel, or initrd directives, press E. To edit the kernel directive only, press A. To use the GRUB command line, press C.

If you press E, select the root, kernel, or initrd directive, and press E to edit it. Initially, the entry cursor is placed at the end of the directive. Use the Home, End, and left and right arrow keys to move through the line. Use the Backspace and Delete keys to erase characters, and type in your changes at the cursor position. Press Enter to save your changes or press Esc to discard them. Press B to start the boot sequence using the changes that you have made.

If you press A, you can edit the root directive. Initially, the entry cursor is placed at the end of the directive. Use the Home, End, and left and right arrow keys to move through the line. Use the Backspace and Delete keys to erase characters, and type in your changes at the cursor position. Press Enter to save your changes and boot the system or press Esc to discard the changes.

If you press C, you can enter GRUB commands. Enter help to see a list of commands. Enter help command to see more information about a specified command.

For more information, enter the info grub command to access the GRUB manual.