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afuse 0.4.1

0. Contents
1. Abstract
2. Basic Usage
3. Pre-populating afuse Root
4. Misc Other Features
5. Important Notes on afuse's Operation

1. Abstract
afuse is an automounting file system implemented in user-space using FUSE.
afuse currently implements the most basic functionality that can be expected by
an automounter; that is it manages a directory of virtual directories. If one
of these virtual directories is accessed and is not already automounted, afuse
will attempt to mount a filesystem onto that directory. If the mount succeeds
the requested access proceeds as normal, otherwise it will fail with an error.
See the example below for a specific usage scenario.

The advantage of using afuse over traditional automounters is afuse runs
entirely in user-space by individual users. Thus it can take advantage of the
invoking users environment, for example allowing access to an ssh-agent for
password-less sshfs mounts, or allowing access to a graphical environment to
get user input to complete a mount such as asking for a password.

afuse is distributed under the GPLv2 license, details of which can be found in
the COPYING file. Particularly, please note that while afuse is intended to be
useful it is provided with ABSOLUTELY NO WARRANTY.

If you are interested in contributing to afuse, please read the HACKING file.

2. Basic Usage
Example invocation using sshfs:

	afuse -o mount_template="sshfs %r:/ %m" \
	      -o unmount_template="fusermount -u -z %m" \

Now try 'ls mountpoint/user@host/'.

To unmount use:

	fusermount -u -z mountpoint/

All sub mounts should be automatically unmounted.

For this example to work, the sshfs invocation must not require user
interactivity (i.e.  asking for a password). So you probably want to be
using something like ssh-agent.

Alternatively, if want interactivity, add -f to the afuse invocation.

3. Pre-populating afuse Root
By default the afuse root directory is empty until a specific access is made to
a directory leading to successful mount. In some cases it may be useful to
pre-populate the afuse root with valid directory names.

To enable root directory pre-population, use the -o populate_root_command
option to specify a command which will provide a list of directory names to
populate the root with.  This program will be run for every directory list
request on the afuse root directory, and should output one dir entry per-line
to stdout. As this program is called repeatedly and for every directory
listing it should not block/pause for an unreasonable amount of time.

Note that when using this mode no actual mounting occurs until a directory
access is made to one of the potential mount-points.

An example of this usage is provided in the afuse-avahissh shell script
(typically installed alongside afuse). This can be started as follows:

	afuse-avahissh mountpoint/

This script will use avahi to automatically populate the root directory with
hosts advertising their sftp service via Avahi. To work correctly both sshfs
and avahi-browse must be installed and available to the script.

4. Misc Other Features
* By default afuse does not attempt to mount a directory on a getattr
  operation. This can be disabled using the -o exact_getattr option. This
  allows getattr to return accurate information but may cause spurious mounts
  when programs are just checking for the existence of files.

* The -o flushwrites option causes write operation on file-systems mounted by 
  afuse to operate synchronously.

5. Important Notes on afuse's Operation
One of the most important things to note about afuse's operation is that
automounted filesystems accessed through afuse are actually accessed by proxy.
Actual mounts are created in an instance specific  directory in /tmp. _ALL_
accesses to automounted filesystems apparently managed by afuse go through
afuse and are proxied onto the real filesystem mounts as appropriate.

While this shouldn't cause any operational problems, it does mean that
operations on afuse automounted filesystems have considerable overhead.  It can
also mean that if afuse is not shutdown cleanly (via an unmount of the afuse
filesystem) a stale directory can be left in /tmp of the form afuse-XXXXXX
(where the X's are random characters).

Hopefully these limitations will be removed in later revisions of afuse.
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