Writing to read-only devices with aufs2

Invisible Ink

Article from Issue 104/2009

Author(s): Klaus Knopper

Add temporary write capability to a read-only device with the stacked filesystem aufs.

Aufs [1] is a stacked filesystem similar to UnionFS [2]. One very common use for aufs is adding "temporary writing" capability to a filesystem residing on read-only media. I use aufs in Knoppix to join read-only data from the compressed Knoppix file (usually located on a CD or DVD) with a read-write filesystem on ramdisk or a USB flash drive. A stacked filesystem creates a stack of existing directories that are "transparent" to the user: Each access to a file is tried for each directory of the stack until it succeeds or the end of the stack is reached.

Even if you aren't building your own Live system, you still might have a practical use for aufs as a means of adding virtual read-write access to files stored on a read-only device. In this article, I describe how to add temporary write capability to a read-only device using aufs.

Gitting Aufs2

Aufs2 comes in two forms: a complete Git-based kernel with aufs2 included and a "standalone" version that contains only the changes that have to be patched into the kernel source.

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