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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?

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up vote 4 down vote accepted

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.

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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 : – Frédéric Grosshans May 4 '11 at 9:22
"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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