Ubuntu – How to add a GRUB2 menu entry for booting installed Ubuntu on a USB drive

bootgrub2usb

I am not asking how to boot the LiveCD from a USB.

I have 2 Ubuntu installations, one on my computer's internal hard drive and another on a USB drive.

Is there a way to add a GRUB2 menu entry (to the GRUB on my internal hard drive) to boot the Ubuntu OS which I have installed to the USB flash drive and have this same menu entry still work after I've upgraded the Linux kernel on the USB installation?

Best Answer

Each time you upgrade kernel on external, you can run this to update boot stanza in grub on the internal drive.

sudo update-grub

But you can also add a boot stanza to grub2's 40_custom that boots the partition, not the specific kernel. Ubuntu installs links in / (root) to boot the most recent install. Adjust example below if necessary to your drive & partition. Boot drive with grub is always hd0, but then other drives are in BIOS reported order which may vary.

Edit with:

gksudo gedit /etc/grub.d/40_custom

then, add:

menuentry "Install on sdb1" {
    set root=(hd1,1)
    linux /vmlinuz root=/dev/sdb1 ro quiet splash
    initrd /initrd.img
}

While above works, I find the drive may change when plugging in a flash drive or any other USB device. So I am converting to use labels.

menuentry "Cosmic 18.10 on sdb12 test" {
    search --set=root --label cosmic_b --hint hd2,gpt12
    configfile /boot/grub/grub.cfg 
}
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