Re: [gentoo-user] Help!!! My system won't boot. (?lvm?) :-(

[Alan Mackenzie]

Hello, Alan.

On Wed, Jan 11, 2023 at 20:16:07 +0000, Alan J. Wylie wrote:
> Alan Mackenzie <acm@×××.de> writes:

> > My system isn't booting.  In particular, most of the SSD partitions
> > won't mount, because they are not under /dev any more.  The root
> > partition, /dev/md125 mounts, but that is all.

> > These partitions are lvm partitions under RAID-1 (software RAID).  They
> > simply fail to appear in /dev/mapper on boot up.

> > I've managed to bring my system up using a Rescue-DVD followed by
> > chroot.  This shows that the partions on the SSD are basically
> > undamaged.

> > I strongly suspect that my emerge update from last night is to blame.

> It was.

> Been there, done that myself.

> Mount your filesystems from the rescue boot and chroot into them.

> Re-emerge lvm2 with the "lvm" flag enabled.

Many thanks, indeed!  That was the cause of my problem, and re-emerging
lvm2 with that USE flag set solved it completely.

> See
> https://www.gentoo.org/support/news-items/2022-11-19-lvm2-default-USE-flags.html

Yes.  There was even a news item about it back in November.  I've read
it again, and it seems too vague to me.  For example, it says:

>>> If you use LVM2 for any partitions, or if you use tools like
>>> 'lvchange', you should enable USE=lvm.

, without saying in detail anywhere what it means to "use" LVM2.  I
wasn't aware of "using" LVM2 when I read that news item, so I just
carried on, blithely unaware of the coming catastrophe.  ;-)

Still, it's OK, now.

> Some of these commands (or similar) in the rescue boot might be helpful:

> mkdir -p /mnt/{usr,var,home,work,boot,dev,sys,proc}

> mount /dev/mapper/vg0-root /mnt
> mount /dev/mapper/vg0-usr  /mnt/usr
> mount /dev/mapper/vg0-var  /mnt/var
> mount /dev/mapper/vg1-home /mnt/home
> mount /dev/mapper/vg1-work /mnt/work

> mount /dev/sda1        /mnt/boot

> mount -o bind /dev     /mnt/dev
> mount -o bind /dev/pts /mnt/dev/pts
> mount -o bind /dev/shm /mnt/dev/shm
> mount -o bind /sys     /mnt/sys
> mount -o bind /proc    /mnt/proc

> PATH=/bin:/sbin:/usr/bin:/usr/sbin \
> SHELL=/bin/bash \
> chroot /mnt

Thanks for that, too.  I actually created a small script with commands
like these when I was installing Gentoo ~5 years ago, and I adapted
that, saving the heavy labour of working out again that the flag in
mount that I need is -o bind.  :-)

> --
> Alan J. Wylie                                          https://www.wylie.me.uk/

> Dance like no-one's watching. / Encrypt like everyone is.
> Security is inversely proportional to convenience

-- 
Alan Mackenzie (Nuremberg, Germany).