How do I restore the ESP on a system (openSUSE 15.1) that was working but now doesn't boot after updating. I tried reinstalling from the DVD but keep getting the message: "/boot/x86-64/loader/linux" not found" (or something like that). I suspect that the ESP is corrupted. Is there some standalone tool for repairing it?

The short answer, no.

To fix a broken ESP partition, you will need to boot the system from a live version of what ever linux you like. Install media usually will do it.

ESP partitions are formatted as fat32 most often. Doc for your system should tell you what you need to replace. You should be able to simply copy and missing or corrupt files from install media. This link: https://wiki.archlinux.org/title/EFI..._the_partition explains most of what you need to know. If the file system is damaged, normal file system tools should be able to fix the file system. Worst case, you can re-create the partition and install it again.

Does this message appear when attempting to boot the DVD? Did you make any changes in the firmware/bios? If you have any usb keys plugged in remove them and then try, assuming the install dvd isn't a usb key.

http://download.opensuse.org/distrib...4/loader/linux is the only instance of x86_64/loader/linux I'm aware of in 15.1, so it's on installation media, not on an installed system. It's the installation kernel. I suggest a good fix should be to do an offline upgrade to 15.2 using NET installation media. 15.1 has been out of support several months. openSUSE's upgrade system IME is excellent. I use it often, far more often than clean, fresh installations. It gets a lot of practice, as it's developed from the openSUSE rolling release Tumbleweed, which uses it as often as daily for some users.