Hey list,
I'm in the process of experimenting with a systemd-based initrd.
However I have two questions concerning the boot process that came up whilst reading the documentation.
If I understand "man 7 bootup" correctly so far the initrd mounts /sysroot based on either the root= kernel parameter or through gpt-auto-generator. At this point /sysroot is mounted. However /sysroot/etc/fstab might have additional entries that need to be mounted in the initrd (marked with "x-initrd").
Next "initrd-parse-etc.service" gets triggered which runs fstab-generator which then mounts all the entries marked with "x-initrd".
If "/usr" is in a separate partition; I would expect it to _need_ to be marked "x-initrd" as you want /usr to be present as soon as you boot up the system. And this causes the "sysroot-usr.mount" unit to be generated and gets pulled in by "initrd-fs.target".
We're now ready to switch-root to the root-filesystem and move to stage-2.
In stage-2, in early boot. "systemd-remount-fs.service" runs; which remounts / and /usr with the actual options in /etc/fstab.
Two questions about this:
1. if sysroot-usr.mount already gets pulled in in the initrd by parsing /sysroot/etc/fstab why do we need to remount /usr in stage-2 with "systemd-remount-fs.service"? Didn't we already parse the correct values from fstab, and hence /usr is already guaranteed to be correctly mounted?
2. relatedly; why cant after "initrd-parse-etc.service" is run sysroot.mount be retriggered with the new options parsed from /sysroot/etc/fstab as well? Then to me it sounds like "systemd-remount-fs.service" is not needed at all for / and /usr. (though maybe still for /sys and /proc)
My gut feeling the answer to this question is "not all initrd's use systemd; so they might not parse /sysroot/etc/fstab so early we need to account for that". Is that the case?
Kind regards,
Arian
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