[systemd-devel] root= ignored

[Felix Miata]

Chris Murphy composed on 2015-01-27 23:29 (UTC-0700):

> Felix Miata wrote:

>> Lennart Poettering composed on 2015-01-28 02:03 (UTC+0100):

>>> Hmm, Fedora doesn't obey root=? That sounds like a bug.

> I'm not sure what it means, Fedora doesn't obey root=. Since a long
> time it uses root=UUID= and this has worked for me.

All current distros whose bootloaders I've used include a root= in each of
their bootloader stanzas. AFAIK, root=UUID= is used in Fedora's Grub2
stanzas. Maybe it went into Fedora's Grub Legacy cmdlines before the switch
to Grub2. I don't remember. I haven't installed any of Fedora's bootloaders
since Fedora dropped Grub Legacy, so don't have first-hand experience from
which to know otherwise.

Most distros do not require use of their own bootloaders to successfully
boot. I've been using openSUSE's Grub Legacy for booting all distros
installed on my own systems ever since Grub2 started becoming distros'
default bootloader. This has worked for all, except as described below.

In the pre-libata days, as I remember, any syntactically correct root= on
cmdline was what would be used to find /etc/fstab and get the root filesystem
up. Included among the possibles valid with post-libata distros have been:

	root=/dev/sdX
	root=/dev/disk/by-label/...
	root=LABEL=...
	root=/dev/disk/by-uuid/...
	root=UUID=...

"What it means" is that traditional cmdline root= option still works with
openSUSE's configured-by-default initrds, but not with Fedora's
configured-by-default initrds. Translated, this means the following process
that works with non-Fedora root partitions fails with Fedora's root partitions:

1-boot anything other than intended logical source partition on a BIOS
multiboot system with 1 HD only
2-clone an existing unmounted logical source/root partition to some other
unmounted partition
3-configure a unique UUID and volume label on the clone
4-mount the clone and adjust its fstab appropriately
5-in the HD's bootloader menu (not the boot menu on the clone), clone the
source stanza and adjust it appropriately to use for the clone, using any of
the above listed (legal) root= forms.

When Fedora is the source and clone, attempting boot of clone using default
initrd produces an emergency shell, unlike openSUSE. To boot a Fedora clone
normally requires a chroot rescue (what I usually do) or a
/boot/initramfs-0-rescue*.img boot to rebuild its normal initrd(s). This
Fedora characteristic in effect produces an undesirable, and likely
unforeseeable by most, stumbling block to at least one backup/restore
scenario that involves no change of hardware that Fedora's Dracut hostonly
configuration seems to suggest would be safe.
-- 
"The wise are known for their understanding, and pleasant
words are persuasive." Proverbs 16:21 (New Living Translation)

 Team OS/2 ** Reg. Linux User #211409 ** a11y rocks!

Felix Miata  ***  http://fm.no-ip.com/