Comment 9 for bug 1899372

I have resolved the issue in my case. This is a server and besides Ubuntu I also have TrueNAS installed to another disk as a backup to get to my files if for some reason I can't get in. What I have discovered is that anytime the disk containing TrueNAS is connected the GRUB scripts for ZFS take a dump and leave the "/etc/grub.d/10_linux_zfs: 404: .: cannot open /tmp/zfsmnt.dCD7rF/etc/os-release: No such file " error. I initially thought that maybe grub-customizer had botched it so I backed up my home and reinstalled the OS leaving out grub-customizer and manually editing my GRUB. I was having a black screen GRUB issue before enabling console mode and when I updated GRUB I noticed the script took a dump again so I thought to eject the disk with TrueNAS and try to update GRUB again so I'm not left in an unbootable state and it solved the issue. So now I have just disabled the port for my TrueNAS backup inside the BIOS and all seems well. The reason that rpool was missing in the grub.cfg is because it was adding the entries under linux instead of linux_zfs scripts. If anybody else has this issue pay attention to the scripts in /etc/grub.d/ to find out where your entries are being generated and disable or remove any other ZFS / Solaris type disks that may be conflicting. Other than that I'm not sure how else to leave the TrueNAS drive enabled and not have GRUB take a dump but in my case it is no big deal considering it is just a backup OS that I can leave disabled.