How to add a GRUB2 menu entry for booting installed Ubuntu on a USB drive?
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?
Solution 1:
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
}
Solution 2:
I found out how to use the UUID of the drive, useful if you have multiple drives plugged in at boot time. Credits to oldfred for his note about /vmlinux
and /initrd.img
symlinks.
Add this to the file /etc/grub.d/40_custom
, replacing UUID=XXXX-YYYY
with the partition UUID (get UUID with command blkid
)
menuentry "Boot from USB Drive" {
set root=UUID=XXXX-YYYY
linux /vmlinuz root=UUID=XXXX-YYYY ro quiet splash
initrd /initrd.img
}