Remove an LVM volume group from the kernel

I FINALLY found it!

The problem: You are messing around with loopback files and volume groups. You've removed the loopback, but the VG stays in the kernel's internal list. vgremove is of course NOT how you get rid of it.

The sane way of doing this is:

vgchange -a n VolGroup00
kpartx -d /dev/nbd0
qemu-nbd -d /dev/nbd0
vgscan

But maybe you killed qemu-nbd by mistake? Or maybe your partition is long gone. Then you need to use dmsetup to remove all traces:

# ls -l /dev/mapper/
total 0
lrwxrwxrwx. 1 root root      7 Mar 18 22:08 GEORGE2-root -> ../dm-0
lrwxrwxrwx. 1 root root      7 Mar 18 22:08 GEORGE2-swap -> ../dm-1
lrwxrwxrwx. 1 root root      7 Mar 19 15:44 Test02-LogVol00 -> ../dm-4
lrwxrwxrwx. 1 root root      7 Mar 19 15:44 Test02-LogVol01 -> ../dm-5
crw-rw----. 1 root root 10, 58 Mar 18 22:08 control
# dmsetup info /dev/dm-4
Name:              Test02-LogVol00
State:             ACTIVE
Read Ahead:        256
Tables present:    LIVE
Open count:        0
Event number:      0
Major, minor:      253, 4
Number of targets: 1
UUID: LVM-zo1BvaMXr6TS1knhxoyjhtItHEaIVH4wGJz2s2w8w24za3486Aa9ur0igGMxpLf7
# dmsetup remove /dev/dm-4
# dmsetup remove /dev/dm-5
# vgscan
  Reading all physical volumes.  This may take a while...
  Found volume group "GEORGE2" using metadata type lvm2

And there was much rejoicing.