On Sunday, 16 June 2019 18:00:12 BST Grant Taylor wrote: > On 6/15/19 7:04 AM, Peter Humphrey wrote: --->8 > > My question is: how much of the bootctl-installed image is essential > > for booting? In other words, if I install the ~amd64 kernel (5.1.9), > > what effect will that have on booting the rescue system; and if > > I install the amd64 kernel (4.19.44), what effect will it have on > > booting the plasma system? > > I think it largely depends on where things are installed to. > > Do the different installs share a common /boot? Or do they have > separate /boot partitions? > > I assume the other file systems are separate e.g. / (root), /home.
The two systems share a /boot partition but are otherwise separate: nothing is common to the two systems. > > In practice, I install the ~amd64 kernel and hope it doesn't affect > > the rescue system too much; and it seems not to. Could I do better? > > I don't know if it's better or not, but here's what I'd do. > > · I'd put each OS on it's own drive (if at all possible). > · I'd have a separate /boot and / (root) for each OS. > · I'd configure UEFI boot menu entries for each OS. The main drive is a 256GB NVMe, with no spare slots for a second. I do have a couple of ordinary SSDs in RAID-1 for data, but they're not significant here. I could have separate boot partitions, but I haven't found a need yet. I do have separate UEFI boot entries. My point is that they boot different versions of the kernel, and I wondered what risk that involved, since the image installed in the UEFI space cannot be the same in the two cases. Mick seems to have answered that. > That way, the only thing that's common between the OSs is the hardware > and the UEFI. They are separate from the time that UEFI boot menu onward. > > I recommend the separate drives so that you can use the OS on the other > drive to deal with a drive hardware issue. > > I /might/ be compelled to try to leverage the two drives for some swap > optimization. I'd probably have a minimal amount of swap on the same > drive as the OS and more swap on the other drive. That way each OS has > some swap in the event that the other drive fails, yet still has more > swap if the other drive is happy. So you benefit from the 2nd drive > without being completely dependent on it. Ah, swap. I have a 2GB swap partition near the beginning of the drive, pri=8, and a 16GB one near the end, pri=4. The latter is supposed to cope with huge compilations like chromium. (I tried USE=jumbo-build recently but it ground to a silent halt. I haven't spent time yet investigating why.) To answer another point, I keep most of my user stuff in its own partition mounted under ~/common. I've done that for many years, since the days before I settled on a permanent distro. I didn't want, say, SuSE fighting with Gentoo for rights to my data. Both backups and general flexibility benefit from this arrangement. -- Regards, Peter.
