Squeeze Dual Root With Single Userspace

[uminded]

I would like to run Debian with multiple roots and share the same /usr directory but am unsure if this is asking for trouble. My ideal setup and reasons are below:

/dev/sda1 100MB /boot
/dev/sda3 4096MB swap
/dev/sda2 400GB LVM

LVM broken up as:
Root_Stable 75GB
Root_Testing 75GB
USR 50GB
Home 200GB

I have my stable 2.6.32-5-686 default kernel for backup with a grub entry to boot the system with either Root_Stable or Root_Testing. I also a working 3.1.5 kernel that can boot with either root.

The whole point of this is I do a lot of modifications and mucking about with the system in general. As I only have one computer so my Root_Stable is a standard netinst install with no modifications while the Root_Testing is a custom debootstrap with no SELinux support. As things become stable I shift the mods into the Root_Stable pretty much the same way Debian has its releases set up.

The main thing I am worried about is how to share the /usr directory. I want access to my applications regardless to the root I am using but I do not know of the many interrelations that are going on in the background and if I ran two roots would apps freak out and start mutilating my data? Wine is a good example, I built from source and installed in /usr/share/wine and it worked great. After a few boots around the different roots now wine does not even load when run from the command line. Is thing an expected side effect of how I want to do things? and if so should I just run two user directories after all?

Thanks!!

[cynwulf]

stable and testing sharing the /usr would not be possible as both distributions will install and update files there. The result would be two broken systems.

You can share home, but even that can be messy, if you don't set up different users for both distributions.

[impert]

This is a late reply, but anyway:
I wouldn't do this.
There will almost certainly be differences between some files in /usr between the different versions,and not just the binaries, but also libraries and dependencies.
Why not just multi-boot, keeping the versions separate, and keeping your data on a shared data folder.
A suggestion:

/dev/sda1 10G Debian stable
/dev/sda2 Extended
/dev/sda3 200G Data
/dev/sda4 150G Backup (better on a separate disc or external HD, but you seem to have 1 HD only)
/dev/sda5 4G swap (you'll probably never use it if you've got plenty of RAM, but it may help in a crash)
/dev/sda6 10G Debian testing
/dev/sda7 10G Spare, for when you want to try another distro
/dev/sda8 10G Spare, for when you want to try another distro

The figures are only meant as a rough guide. If you don't keep anything in your $HOME folders apart from config files and a few symlinks to the Data foldeer, you'll find that 10G is fine for most distros. I keep my .mozilla and .evolution folders in the Data folder, there is an occasional hiccough with bookmarks and sometimes mail owing to changes in versions, but if you backup as you should you can always get this stuff back.
Incidentally, you don't really need a separate /boot primary partition if you don't have Windows or other OS not bootable by Grub.
I'd also suggest putting the Grub from stable in the MBR, Grub for the others in their own root partition and booting them by chainloading. Grub legacy is better for this than Grub2.