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Summary of what I need:

  1. I want install 3 different versions of Ubuntu on a computer.
  2. I would like to be given a choice of which OS to boot every time I turn on my computer.
  3. I would like to share Documents, Downloads, Desktop files, etc. between them. Basically, anything that can be shared that won't create problems by being shared between the operating systems. I would like this to be a completely separate disk (physically) where the OSs will be installed.

Note: The reason I am doing this is because each OS is going to have different tools to work on the same data. Unfortunately, many tools I need are simply not compatible with 16.04 yet (and might never be), and I don't have the time to try to hack everything into 16.04 if the normal setup fails.

I have googled this problem quite a bit and either the answer is really old (don't know if the answer is still valid or not), or it assumes I want/have a Windows boot as well, or the steps simply don't seem to have enough detail so I can follow them step-by-step (how to manually partition a disk to perform an installation is somewhat confusing to me). I found this blog article on sharing data between distros without sharing the things that you want to keep separate. http://www.linuxtoday.com/blog/2009/08/painless-linux.htmlPainless Linux Multi-boot

I'm pretty sure I can do the steps in this article without much difficulty, and I'm going to assume this blog article describes a good way to share data between Ubuntu distros. If you know of a better solution or why this is a bad one please share. I'm not emotionally attached to any particular solution at the moment and don't have any constraints on the solution either, but I need to start the discussion somewhere. Unfortunately, this article doesn't completely explain the issue I am working on, but I feel it is going in the right direction.

I want to install Ubuntu 14.04, 15.10, 16.04 (desktop versions) on one machine and no Windows installations. I'm assuming I should install them all on the same disk (which is a 250GB SSD), then use a separate disk for sharing/storing data as described in the linked blog article. Although, I have plenty of disks available if each OS should preferably have its own separate disk.

Anyhow, if anyone knows of a tutorial that will fill in the gaps in doing this please share it. I would prefer a link to a step-by-step tutorial so I can learn from it and save it for later.

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  1. No problem.
  2. That is normal when you have 2 or more operating systems.
  3. Pretty simple. Assume you have an empty disk and boot into the installation and are at the partitioning setup.

    • create 4 partitions. Ubuntu OS needs a root of about 25Gb that can include a /home/. 25Gb is more than enough if you keep your own data outside of the system (ie. out of / and out of /home).
    • mount the 1st of those 4 as /
    • mount the bottom one as /data/ or whatever name you want. Make it ext4.
    • install system 1.

  • when done install system 2.
  • mount the 2nd partition as /
  • mount the bottom one as /data/ -without- formatting.

  • when done install system 3
  • mount the 3rd partition as /
  • mount the bottom one as /data/ -without- formatting.

Some extras:

  • Try to avoid sharing /home/.* and just stick to the subdirectories. This will avoid any kind of conflict between releases.
  • if you want you can expand each of these with a boot.
  • Opt for adding a partition for /opt. If you install 3rd party software that is the most ideal directory to use and there is a good chance you can then use the software on all 3.
  • use the same usernames and userIDs on all systems.
  • copy from 1 system all the directories in /home/ to /data/.
  • When done remove all the -directories- in each of the /home/'s and edit .config/user-dirs.dirs in each of the systems to point to /data/.

And you are done.

I do believe though there is an easier method nowadays.

  • Install 16.04 as explained at the 1st part with a /data/ disk. It is the latest LTS so has a long support.
  • Install virtualBox or VM Ware. Install 2 systems into that.
  • Install guestadditions for VBOX or WM Ware tools for VM Ware and mount the /data/ in the 2 systems.

Big plus for this: you can start all 3 systems at the same time. No picking a system at boot time. Adding more other operating systems is a lot easier an removing a system it also a lot easier. Backup means creating a copy of your container. And you can even multiply containers.

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I suggest you first install Ubuntu 14.04 and during installation make 3 partitions of 250gb ssd each disk formatted as ext4 and mount one partition as / , also format the other disk where you want to save data as /home . Then install Ubuntu 15.04 in the second partition of 250gb ssd and format it as ext4 and mount it as / and mount the other disk where you want to save data which is home for Ubuntu 14.04 as /home (no need to format it). Similarly install Ubuntu 16.04 on the third partition of 250gb ssd and mount it as / and mount the other disk which is used as home for other 2 Ubuntus as /home.

This way your home is mounted on other disk and data in that disk is shared among all Ubuntus. I have earlier used the same approach to share one home directory with Ubuntu and fedora. It will work fine.

Note: Keep username for all Ubuntu the same. You need to install grub and make sure it detects all OSes

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    I do not suggest sharing /home. Depending on version or configuration you may get conflicts in the user configuration & data. Some have had it work with two identical versions, but updates in a newer one may not have compatible settings with older versions of software. Example: When I updated to 16.04 it keepassX converted my encrypted file to a new format that was not compatible with the older versions. – oldfred Jun 25 '16 at 19:05
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While you can do this, it may be more convenient to use chroot jails to hold your multiple installations of Ubuntu. This has a downside that you will need to use the same kernel for all of your installations, but the upside is that you can use them at the same time, without needing to reboot, and don't need to partition your disks for the individual installations.

There are full instructions on the Ubuntu wiki.

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