Copy filesystem.squashfs (only) to ram

[Alex King <alex@king.net.nz>]

I'm wanting to use a debian-live image to wipe the disks on some systems 
being decommissioned.  To do that, I believe I need to copy 
filesystem.squashfs into ram so it isn't sitting on a disk to be wiped.

For various reasons (e.g. problems with the dhcp server) netbooting 
isn't possible.

I'm writing a grub configuration that loads vmlinuz and initrd from 
/boot, this is successful.

I tried using the live-boot(7) "ip=" and "fetch=" paramaters to 
configure IP and fetch the filesystem from a webserver, however after 
booting it was still trying to do network autoconfiguration and drops to 
busybox saying that the network was not configured.

If I pre-download filesystem.squashfs to a local filesystem, it works OK 
but doesn't load into ram.

I tried live-boot(7)"toram" paramater.  This actually worked on my test 
machine, but to my surprise it copied the whole 4G root filesystem to 
ram instead of just filesystem.squashfs.  While it worked on this system 
(albeit wasting a lot of time and RAM from the 16G on this machine), it 
would not work in other cases where the root filesystem may be 500G and 
RAM only 4G.

How can I arrange to have filesystem.squashfs copied into ram?

Thanks,
Alex