mjhjmtu

I deleted a partition on my hard disk, causing the partition numbers of the 2 Linux installations to decrement. When attempting to boot the computer I get the message error: no such partition and I am dropped to the grub rescue> prompt. How can I fix this?

You could try running update-grub either at the rescue prompt or from a Live USB/CD. Don´t know if it will work but it is a good starting point. Best thing to do is always backup before modifying partitions.

Good way to backup is boot on a Live USB and run

dd if=/[location of computer harddrive (example /sda)] of=[location of external harddrive (example /sdb)]

Hopefully update-grub helps :)

@River-rush is right of course, fixing the numbering in your grub config to reflect the current situation will allow you to boot. As soon as you assign that disk space to a new partition though you'll have to renumber again. Presumably you want to do something with it?

You could boot from a rescue disk and create a partition in the space where the old one was, which would put your numbering back how it was before, and allow you to boot with the existing grub config.

If you are extending an existing partition to fill the space, then go with the approach of fixing your grub config.

Thanks to the existing answers. Since I used the partition number, I used the guide from https://help.ubuntu.com/community/Grub2/Troubleshooting:

1. 
   set prefix=(hdX,Y)/boot/grub where X is hard drive number starting with 0 and Y is known partition number


2. 
   set root=(hdX,Y) with the same numbers


3. insmod normal


4. normal

From here, I pressed e to edit the boot parameters and changed the partition number in 5 places on 3 lines.

It booted normally and I then ran update-grub.

I found out that despite the rather cryptic error given by parted, you should not restart and should instead run update-grub.