questions about /usr

[hlivy]

I've read about having two linux distros sharing one /home, but what about /usr?
Actually I have three questions:

1. If you move on to a new version of your distro by fresh install, what happens to the applications you installed in /usr before, do you have to install them all over again?

2. If I have a separate /usr partition, and I have two linux distros installed, will both of them be able to read and write on it?

3. If I have a separate /usr partition, and I update my distro to a new version, will I still be able to use the applications in /usr? I.e., will there be dependency issues?

Thanks for reading, any feedback would be appreciated

[i92guboj]

I've read about having two linux distros sharing one /home, but what about /usr?

It would be much easier to beat a tank with your bare hands.

1. If you move on to a new version of your distro by fresh install, what happens to the applications you installed in /usr before, do you have to install them all over again?

If you do a clean installation, usually your system partitions must be formated, otherwise you will end with a lot of crap in your installation. Of course, you need to reinstall everything.

There are some distros that might offer an option to update your current installation, that's another story, and it should work ok and respect everything that you had installed (whether it efectively does and doesn't break anything is a completely different story, and that depends usually on que quality of your distro and the installer).

2. If I have a separate /usr partition, and I have two linux distros installed, will both of them be able to read and write on it?

Sure, and they will most like conflict and drive you insane. You can't do that. Seriously.

Each distro will install its files into /usr without knowing anything about the other distro. It might overwrite or erase files from the other distro, and there's nothing you can do about it, because each distro has its own installer and they don't know anything about each other.

Each distro will ship different versions of core libs that will break ALL the binaries for the other distro. This is definitely not a good idea.

[hugortega]

But, if you're installing applications manually (i.e. not using your distro package management system), it's a good idea to have another partition (e.g. /usr/local/) ... so, you can save the work of installing again or, maybe, sharing between distros... but, for applications installed automatically, it's not a good idea, as i92guboj says.

[valan]

It is possible to share a /usr partition, but it wouldn't be easy. You would have 2 distros fighting over the same directories and files, and they may not easily be able to tell what is or isn't installed and they'll end up confusing each other. Also, different versions of programs and libraries which may be used and/or needed could play mind games with you. I personally don't even see the use of 2 different distros one one machine, what you can do with one you can certainly do with the other.

[hlivy]

I do install applications manually most of the time. But it sounds like it's gonna be too much a hassle for two distros to share them. I won't bother with a separate /usr partition then.

As for two distros on one machine, one for use one for experiments, in case I screw something up

Thanks for the replies guys, they are very helpful for me.

[valan]

For experimentation, I prefer to install one in a virtual machine. That way it is completely isolalated from the hardware and the other install, and I can use my computer for other things at the same time.