Grub Bootloader

Table of Contents

1. Word of advise
2. Hide or edit timer on GRUB bootloader
3. Boot to last-used OS
4. Rename OS menuentry
   1. Easy way
   2. A bit complicated way
5. Boot to OS using GRUB shell

Word of advise

• Always, always create backup of config file.
• Make sure you have bootable usb drive to fix if anything goes wrong.

To create backup of original setting file, run:

cp /etc/default/grub /etc/default/grub.orig

Hide or edit timer on GRUB bootloader

1. Edit /etc/default/grub to these setting

    GRUB_TIMEOUT=0 
    # Change the number (in seconds) to shorten or prolong grub screen.
   

2. Then update grub bootloader

    sudo update-grub
   

Boot to last-used OS

1. Edit /etc/default/grub to these setting

    GRUB_DEFAULT=saved
    GRUB_SAVEDEFAULT=true
   

2. Then update grub bootloader

    sudo update-grub
   

Rename OS menuentry

Either way is fine, it depends on one’s preference actually.
However, do note that changing these setting will prevent grub to update kernel.
If you want to update kernel, just give the file its execution right and run sudo update-grub.

Easy way

1. Edit file /boot/grub/grub.cfg

    menuentry "Something" {
        set root=(hdX,Y)
        -- boot parameters --
    }
   

2. Change that Something to your desired name.
3. Do not run sudo update-grub. Otherwise grub.cfg will be regenerated to grub-script setting.

A bit complicated way

1. Open file /boot/grub/grub.cfg and look for these headers.

    ### BEGIN /etc/grub.d/10_linux ###
        ***
        ***
       
    ### BEGIN /etc/grub.d/30_os-prober ###
        ***
        ***
   

2. Copy your desired menuentry and paste-append it to /etc/grub.d/40_custom.
   The grub man says to be sure to not leave empty line at the end of file. I haven’t tried it, so I don’t know what happen if we ignore the warning.
3. Then revoke executable right for these files.

    /etc/grub.d/10_linux
    /etc/grub.d/30_os-prober
   

4. And lastly, update grub to make changes.

    sudo update-grub
   

Boot to OS using GRUB shell

1. Identify /boot partition

    grub> ls
    # expected output
    # (hd0) (hd0,1) (hd0,2) ...
   

2. Adapt to these commands to boot to OS

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