My goal is to use an AuFS read only branch as another read only branch:

I've got a directory dir0, then I make :

mount -t aufs -o br=dir2=rw:dir0=ro none dir1

This gives me

- dir0
- dir1  #read only dir0
- dir2  #write layer of dir1

I now want to use dir1 this way:

mount -t aufs -o br=dir4=rw:dir1=ro none dir3

To get

- dir0
- dir1  #read only dir0
- dir2  #write layer of dir0
- dir3  #read only dir1 (dir1 + dir2)
- dir4  #write layer of dir3

I'm using ubuntu 12.04 and this should work according to aufs-tools man page:

Any filesystem can be a branch, But some are not accepted such like sysfs, procfs and unionfs. If you specify such filesystems as an aufs branch, aufs will return an error saying it is unsupported.

But I got this error:

mount: wrong fs type, bad option, bad superblock on none, missing codepage or helper program, or other error (for several filesystems (e.g. nfs, cifs) you might need a /sbin/mount. helper program) In some cases useful info is found in syslog - try dmesg | tail or so

and dmesg gives me

aufs test_add:231:mount[3346]: unsupported filesystem, (aufs)

Am I missing something here ? Regards, Robin

1 Answer 1


Seems that it is currently not possible.

However, Overlayfs does it very well and seems to be the union FS of choice in ubuntu and in the future 3.10 Linux kernel.

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