Migrating LVM volumes to a new machine

[Mark Fletcher <mark27q1@gmail.com>]

Hello

I would like to understand how to move a LVM VG from one machine to 
another, when the disk to be moved contains filesystems key to the 
source system. I have read section 13.6 of the LVM HOWTO which talks 
about moving VGs. However the context of my situation is I am 
cannibalising an old machine and moving the VG that contains the LVs 
mounted on /, swap and /home of the source machine. That, apart from the 
non-LVM /boot partition, is all that is on this SSD.

The disk will not be the primary disk on the new machine, and the new 
machine's /, swap and /home will be elsewhere, but I will want to be 
able to access the current contents of the disk from the old machine on 
the new machine for a period of time before I decide to wipe it. I feel 
like I can't follow the instructions in the HOWTO because it wants me to 
unmount the file systems, export the LVs and so on, on the old machine 
before moving the disk, and I don't see how I can do that on a system 
that is expecting to use those file systems to operate.

I thought of booting a live system from a USB stick, so the affected LVs 
aren't mounted or in use, but then I'll face the problem of how to get 
the live system to be aware of the LVM setup existing on the SSD.

I guess the bottom line is I am missing some understanding of how LVM 
works in detail, and in particular how a machine that didn't create a 
particular VG and its contents can nonetheless be made to recognise it. 
Can anyone fill me in?

Thanks 

Mark