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According to the Filesystem Hierarchy Standard (FHS), /usr is "shareable between various FHS-compliant hosts" (and /usr/share is even shareable between different architectures of the same OS).

Are there any Linux distributions whose installers support this shareability ?

What I would expect as "support" is that one can configure the shared directory as a network drive in the installer. In the installation process the file system is writeable and after rebooting, it is mounted read only.
The second installer sees the files that are already there from the first installation and then just uses them instead of trying to delete or overwrite them or complaining that the directory is not empty.

But then comes the tricky part:

  • What if one of the files must change when it comes to an upgrade ?
  • How can the second system using the shared directory continue working while the first system is doing any changes ?
  • How about automatic nightly security updates under /usr/lib ?

Or am I completely wrong and sharing /usr means that one cannot do any updates with the distribution installer/updater, making the complete installation de-facto read only ?

  • Think about multiple machines with one machine as the "master" which has the /usr as a local FS and all the other machines getting it as a R/O mount. What under /usr gets written to aside from updates? – ivanivan Mar 2 at 23:46
  • Most package managers (and thus installers) use datafiles in /var to understand what is under package management. If you want to share /usr then you're likely wanting to create a custom deployment system unique to your environment. I don't know of any 'out of the box' setups designed for this. You might want to look into some of the "diskless" solutions for the client machines. – Stephen Harris Mar 3 at 0:54

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