I want Linux's OverlayFS to behave like AUFS when writing to a lower file. I want it to write through to the lower directory. For example, I have two files named L/lower and U/upper.

mount -t overlay -o lowerdir=L,upperdir=U,workdir=W overlay X

This merges L and U into a single OverlayFS directory named X. So now the two files are accessible as X/lower and X/upper.

Then I modify the lower file through the OverlayFS directory. This is where it misbehaves on me:

echo 'This is a modification' >> X/lower

It does not actually modify the lower file L/lower. Instead it creates a new upper file called U/lower and writes my modification there. This is not what I want. I want X to serve as a convenient, single access point for editing purposes.

How can I make the modification to X/lower write through to L/lower?

  • lower is readonly. thats how it works. you can recursively mount overlay over overlays, though. – mikeserv Oct 29 '15 at 22:31
  • I've posted a couple of answers to my own question (unix.stackexchange.com/q/393930) which covers this topic. – ejm Sep 23 '17 at 2:50

You can write to the underlying directory by not using the created overlay to access the file (the directory "X" in this case). Do it with:

echo 'This is a modification' >> L/lower
  • That wouldn’t be done through the overlay, however, which is what I ask about. I’d like X/lower to be a single point of access for editing purposes regardless of whether the file actually sits in L/ or in U/; so apparently merging the two directories while actually keeping them apart. – Michael Allan Dec 5 '19 at 0:08

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.