From Gentoo Wiki
Jump to:navigation Jump to:search
Other languages:

Overlayfs (Overlay Filesystem) is an in-kernel attempt at providing union file system capabilities on Linux. OverlayFS differs from other union filesystem implementations in that after a file is opened all operations go directly to the underlying, lower or upper, filesystems. This simplifies the implementation and allows native performance in these cases.[1]

The option to enable OverlayFS exists in Linux kernels 3.18 and higher.[2]



KERNEL Enable OverlayFS (OVERLAY_FS) support
File systems  --->
   [*] Overlay filesystem support


Once enabled in the kernel OverlayFS can be controlled using the mount command.

To mount an overlay filesystem:

root #mount -t overlay overlay -o lowerdir=lowerdir,upperdir=upperdir,workdir=workdir mountpoint
Multiple lowerdir entries, colon (:) separated, can be used. When doing so, upperdir and workdir can be omitted to make a read-only mount.
When included, both upperdir and workdir have to reside within the same filesystem.

See also

  • Aufs — an advanced multi-layered unification filesystem.
  • SquashFS — an open source, read only, extremely compressible filesystem.
  • Wikipedia:UnionFS — The original union filesystem.

External resources