[CentOS] Is it possible to lvrename the current root partition?

[Ross S. W. Walker]

Alfred von Campe wrote:
> 
> On May 2, 2008, at 17:24, Ross S. W. Walker wrote:
> > Sure you can do all this from rescue mode off the first CD.
> >
> > Boot the cd type in 'linux rescue' and continue to the command prompt.
> 
> First, thanks for the detailed list, Ross.  It was very helpful.  I  
> was able to rename both the VG and the LVs, but it was slightly more  
> complicated than the items on the list.
> 
> > 1) make sure swap isn't using the swap lv
> > 	- swapoff -a
> 
> What I did was say "Skip" when the rescue image asks you if you want  
> it to find existing Linux installations and mount them under /mnt/ 
> sysimage.  The reason I did this was that if you let it mount your  
> partitions, you need to go through a lot of additional steps to get  
> everything under /mnt/sysimage unmounted, and nothing in there is  
> needed to do the rename (unless you want to rename the VG -- 
> see below).
> 
> > 2) unmount all lvs mounted
> > 	- umount /mnt/sysimage/boot
> > 	- umount /mnt/sysimage
> 
> Not needed because of what I did in step 1, but there are additional  
> mount points to unmount if you do let the rescue image do the mounts  
> (do a "mount | grep  sysimage" to find all the mount points).
> 
> > 3) mark all lvs as unavailable
> > 	- lvchange -a n <vgname>
> 
> This step is indeed required unless you chose to skip the mounting  
> of /mnt/sysimage altogether.  Do a "lvm lvscan" to find out 
> which LVs  
> are active (and use "lvm lvchange" as described below).
> 
> > 4) rename the volume group
> > 	- vgrename <oldvgname> <newvgname>
> 
> Well, vgrename is not part of the rescue disk.  So if you want to do  
> this, you will have to mark the root LV as available, mount it, and  
> then copy /mnt/<mountpoint>/usr/sbin/vgrename to /tmp.  Then 
> you have  
> to unmount the root partition and mark the LV as unavailable.
> 
> > 5) rename the logical volumes
> > 	- lvrename <vgname>\<oldlvname> <newlvname>
> >
> > 6) repeat #5 as necessary
> 
> The lvrename binary (symbolic link) does not exit in rescue mode, so  
> you will have to type "lvm lvrename" (and "lvm lvchange", etc.).   
> Also, you have to use a forward slash here.
> 
> >
> > 7) re-activate all the lvs
> > 	- lvchange -a y <vgname>
> 
> Remember to use the new names.
> 
> > 8) re-mount the root and boot lvs,
> > 	- mount /dev/<vgname>/<rootlv> /mnt/sysimage
> > 	- mount /dev/<vgname>/<bootlv> /mnt/sysimage/boot
> 
> I think this part worked as is.
> 
> > 9) chroot to the mounts with, 'chroot /mnt/sysimage /bin/bash'
> 
> Before I could do this, I had to use mknod to create the device  
> entries in /mnt/sysimage/dev/mapper/<vgname>-<lvname> and the  
> symbolic links in /mnt/sysimage/dev/<vgname>/<lvname>.  Make sure the  
> symbolic links point to /dev/mapper/... and not /mnt/sysimage/dev/ 
> mapper/...  I don't remember if this was required to mount it while  
> in rescue mode or to make the system bootable again.  But I remember  
> that I had to do it.
> 
> > 10) edit /etc/fstab
> >
> > 11) edit /boot/grub/grub.conf
> >
> > 12) remake the initrd
> > 	- mkinitrd -f /boot/initrd-$(uname -r).img $(uname -r)
> 
> You will have to type the release version of the kernel instead of  
> relying on the output of uname -r.
> 
> It turns out that I can skip steps 7-12 since I plan to upgrade the  
> systems from CentOS 4.6 to CentOS 5.1 immediately after doing the  
> rename, and the installer (anaconda) will take care of all these  
> details.   I just had to adjust my kickstart scripts to use the new  
> names.
> 
> Anyway, thanks again for all the help.  I'm starting to upgrade my  
> two dozen or so desktops to CentOS 5.1 using the new VG and LV names.

Thanks for updating the points with your experience. I wrote it
from memory, so was bound to miss something. Maybe it can be
incorporated into a general how-to.

Yeah the lvm included in the busybox rescue is a little kludgy,
that's why I typically use the FC8 rescue CD as it is a little
more refined.

You can try making symlinks to 'lvm' for lvrename and vgrename
or even hard links and it should provide that function.

Good idea to skip the mounting, because once it's mounted it's
a PITA to umount everything and re-mount it.

Of course if your performing an upgrade there is no need to
regenerate the initrd as a new one is created during install.

-Ross

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