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William Oliver avatar Ubuntu

Grub forcing me to boot from flash drive

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William Oliver

So, I had this bright idea to save me from toting my laptop between work and home. I'd get a usb SSD drive, install kubuntu and sync my /home directory to it. That way I could just carry the usb drive to work, plug it in a laptop there, and run it as a near-clone of my laptop at home.

I got a live distro of kubuntu and installed it on the usb ssd drive using my home laptop, and it worked fine. When I have the usb dive plugged in my home computer, I can boot from either the usb drive or the internal drive, and it does great. However... if I pull out the usb drive, and try to boot just using the internal hard drive, I just get the grub command line.

If I type "boot," I get the error "You need to load the kernel first." if I type "ls" I get: (proc) (hdo) (hdo,gpt2) (hd0,gpt1)

Here's the df from booting with the usb ssd:

% df
Filesystem      1K-blocks      Used  Available Use% Mounted on
tmpfs             3256960      2352    3254608   1% /run
/dev/sda2      1921208544 274306084 1549236620  16% /
tmpfs            16284792     14436   16270356   1% /dev/shm
tmpfs                5120         4       5116   1% /run/lock
/dev/nvme0n1p1     523248      5368     517880   2% /boot/efi
tmpfs             3256956        72    3256884   1% /run/user/1000
/dev/nvme0n1p2  982862268 307631972  625229964  33% /mnt/hd

Note that /boot/efi is on the internal drive (nvme0n1p1), which I don't really want -- since it means I can't really take the drive to work and boot on a random laptop.

Here's the /boot directory on the flash:
/boot$ ls
config-5.19.0-21-generic      memtest86+.elf
config-5.19.0-29-generic      memtest86+_multiboot.bin
efi                           System.map-5.19.0-21-generic
grub                          System.map-5.19.0-29-generic
initrd.img                    vmlinuz
initrd.img-5.19.0-21-generic  vmlinuz-5.19.0-21-generic
initrd.img-5.19.0-29-generic  vmlinuz-5.19.0-29-generic
initrd.img.old                vmlinuz.old
memtest86+.bin

Here's the /boot directory on the internal drive:

/mnt/hd/boot$ ls
config-5.15.0-48-generic             memtest86+.elf
config-5.15.0-57-generic             memtest86+_multiboot.bin
config-5.15.0-58-generic             System.map-5.15.0-48-generic
config-5.18.0-051800rc1-generic      System.map-5.15.0-57-generic
efi                                  System.map-5.15.0-58-generic
grub                                 System.map-5.18.0-051800rc1-generic
initrd.img                           vmlinuz
initrd.img-5.15.0-48-generic         vmlinuz-5.15.0-48-generic
initrd.img-5.15.0-57-generic         vmlinuz-5.15.0-57-generic
initrd.img-5.15.0-58-generic         vmlinuz-5.15.0-58-generic
initrd.img-5.18.0-051800rc1-generic  vmlinuz-5.18.0-051800rc1-generic
initrd.img.old                       vmlinuz.old
memtest86+.bin

So, I need to tell grub on the usb ssd not to look to the internal drive for /boot/efi, and I need to tell grub on the internal drive not to look to the usb drive to find out where the kernel lives.

I think.

I have to say that this all seems a mystery to me, and I have yet to find a tutorial that explains it well.

How can I do this? As an aside, I have lots of backups, so I'n not averse to wiping both drives and starting from scratch, but I don't want to repeat the same mistakes.

Thanks.

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Organic Marble avatar
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Organic Marble
You need to fix grub in both places by doing this in both places: https://askubuntu.com/a/831241/243321 When fixing the home PC, use a different live USB than the persistent one you take to work (just to avoid confusion - you *could* use the same one, but the procedure is confusing enough already).
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oldfred avatar
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oldfred
If you did a full install, it puts boot files on internal drive's ESP. Old but valid bug with work arounds. https://bugs.launchpad.net/ubuntu/+source/ubiquity/+bug/1396379 If you have ESP on external drive, you can just reinstall grub, by updating fstab (make sure its remounted) with external drive's ESP & `sudo grub-install` or Boot-Repair. Or add ESP. Or reinstall & Remove esp flag from Windows before install to second or external drive - Tim Richardson https://askubuntu.com/questions/16988/how-do-i-install-ubuntu-to-a-usb-key-without-using-startup-disk-creator
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William Oliver avatar
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William Oliver
The answer by Organic Marble worked for me. Unfortunately, I don't see a check mark next to it, so I can't mark it as answered. Since it worked, I did not try Tim Richardson's method. Once again, any pointers to a good tutorial on this would be appreciated.
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C.S.Cameron avatar
cn flag
C.S.Cameron
My wife has been doin similar to what you want to do for quite a while. See ubfan1's answer here: https://askubuntu.com/questions/991189/using-existing-home-directory-from-a-bootable-external-drive
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William Oliver avatar
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William Oliver
Yes it does. It can be flagged as a duplicate -- though I didn't *know* it was a duplicate until it was pointed out.
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