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.\" ----------------------------------------------------------------------
.TH aufs 5 \*[AUFS_VERSION] Linux "Linux Aufs User's Manual"
.SH NAME
aufs \- advanced multi layered unification filesystem. version \*[AUFS_VERSION]

.\" ----------------------------------------------------------------------
.SH DESCRIPTION
Aufs is a stackable unification filesystem such as Unionfs, which unifies
several directories and provides a merged single directory.
In the early days, aufs was entirely re-designed and re-implemented
Unionfs Version 1.x series. After
many original ideas, approaches and improvements, it
becomes totally different from Unionfs while keeping the basic features.
See Unionfs Version 1.x series for the basic features.
Recently, Unionfs Version 2.x series begin taking some of same
approaches to aufs's.

.\" ----------------------------------------------------------------------
.SH MOUNT OPTIONS
At mount-time, the order of interpreting options is,
.RS
.Bu
simple flags, except xino/noxino and udba=inotify
.Bu
branches
.Bu
xino/noxino
.Bu
udba=inotify
.RE

At remount-time,
the options are interpreted in the given order,
e.g. left to right.
.RS
.Bu
create or remove
whiteout-base(\*[AUFS_WH_BASE]) and
whplink-dir(\*[AUFS_WH_PLINKDIR]) if necessary
.RE
.
.TP
.B br:BRANCH[:BRANCH ...] (dirs=BRANCH[:BRANCH ...])
Adds new branches.
(cf. Branch Syntax).

Aufs rejects the branch which is an ancestor or a descendant of another
branch. It is called overlapped. When the branch is loopback-mounted
directory, aufs also checks the source fs-image file of loopback
device. If the source file is a descendant of another branch, it will
be rejected too.

After mounting aufs or adding a branch, if you move a branch under
another branch and make it descendant of another branch, aufs will not
work correctly.
.
.TP
.B [ add | ins ]:index:BRANCH
Adds a new branch.
The index begins with 0.
Aufs creates
whiteout-base(\*[AUFS_WH_BASE]) and
whplink-dir(\*[AUFS_WH_PLINKDIR]) if necessary.

If there is the same named file on the lower branch (larger index),
aufs will hide the lower file.
You can only see the highest file.
You will be confused if the added branch has whiteouts (including
diropq), they may or may not hide the lower entries.
.\" It is recommended to make sure that the added branch has no whiteout.

Even if a process have once mapped a file by mmap(2) with MAP_SHARED
and the same named file exists on the lower branch,
the process still refers the file on the lower(hidden)
branch after adding the branch.
If you want to update the contents of a process address space after
adding, you need to restart your process or open/mmap the file again.
.\" Usually, such files are executables or shared libraries.
(cf. Branch Syntax).
.
.TP
.B del:dir
Removes a branch.
Aufs does not remove
whiteout-base(\*[AUFS_WH_BASE]) and
whplink-dir(\*[AUFS_WH_PLINKDIR]) automatically.
For example, when you add a RO br