I'm interested in knowing the answer to this unanswered question from the Ubuntu Forums:

I am trying to get one folder to display the content of two other folders. ... I am a bit troubled by the different options.

  • There is unionfs, which seems to be available only via fuse in Ubuntu server, and not recommended as it's said to be buggy.
  • There is aufs, which people are campaigning hard to get out of the kernel.
  • There are talks about a VFS solution being developed but I can't find anything about it.

What is the best solution to use?

Which union filesystem should I choose in order to have the best support in current and future releases of Ubuntu?


Aufs is the union filesystem used by default for schroot and the LiveCDs. That's what I'd use, but you're right - there's not really an upstream union filesystem solution that I'm aware of.

  • Aufs does appear to be the least poorly supported, for this reason. It's a shame — there isn't even a manpage for it! – ændrük Jun 2 '11 at 15:30

I can't help you pick the best solution, but for information on the vfs solution and a well written series of articles on linux union mounts, have a look at A brief history of union mounts by Valerie Aurora. According to a post on her blog in January, it is not quite done yet.

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    Just to add a link to Valerie Aurora's page on union mounts : valerieaurora.org/union – Frédéric Grosshans May 4 '11 at 9:22
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    "I can't help you pick the best solution" — Fortunately, I only ask which filesystem is best supported. It's the difference between "Is Safari or Firefox better?" and "Is Safari or Firefox better supported in Ubuntu?" – ændrük May 4 '11 at 13:09

Added also here: Cannot mount second drive at "/"

Update: the overlayfs file-system has been promoted to standard kernel for version 3.18. So now there is an official union-type solution for linux; userspace utility to simplify its use will surely follow. For now, documentation is in the kernel tree at Documentation/filesystems/overlayfs.txt.

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