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Developer(s) Miklos Szeredi, Open Source Community
Full name Overlay File System
File system permissions POSIX
Supported operating systems Linux, FreeBSD and NetBSD

In computing, OverlayFS is a union mount filesystem implementation for Linux.


The need and specification of a kernel mode Linux union mount filesystem was identified in late 2009.[1] The initial RFC patchset of OverlayFS was submitted by Miklos Szeredi in 2010.[2] By 2011, OpenWrt had already adopted it for their use.[3]

It was merged into the Linux kernel mainline in 2014, in kernel version 3.18.[4][5] It was improved in version 4.0, bringing improvements necessary for e.g. the overlay2 storage driver in Docker.[6]

While most of Live CD linux distribution used Aufs as of November 2016, Slackware used overlayfs for live CD.[7]


The main mechanics of OverlayFS relate to the merging of directory access when both filesystems present a directory for the same name. Otherwise, OverlayFS presents the object, if any, yielded by one or the other, with the "upper" filesystem taking precedence. Unlike some other overlay filesystems, the directory subtrees being merged by OverlayFS do not necessarily have to be from distinct filesystems.[8]

OverlayFS supports whiteouts and opaque directories in the upper filesystem to allow file and directory deletion.[8]


  1. ^ Aurora, Valerie (March 18, 2009). "Unioning file systems: Architecture, features, and design choices". LWN.net. Retrieved 2018-01-17. 
  2. ^ Edge, Jake (September 1, 2010). "Another union filesystem approach". LWN.net. Retrieved 2018-01-17. 
  3. ^ Corbet, Jonathan (June 15, 2011). "Debating overlayfs". LWN.net. Retrieved 2018-01-17. 
  4. ^ "OverlayFS commit to Linux". 
  5. ^ "OverlayFS Proposed For The Linux 3.18 Kernel". 
  6. ^ "Select a storage driver - Docker". archive.is. 2016-12-06. Archived from the original on 2016-12-06. Retrieved 2017-06-05. 
  7. ^ "slackware:liveslak - SlackDocs". docs.slackware.com. Retrieved 2017-06-05. 
  8. ^ a b "OverlayFS documentation". kernel.org. 

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