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General Information
===================
FUSE (Filesystem in Userspace) is a simple interface for userspace
programs to export a virtual filesystem to the linux kernel. FUSE
also aims to provide a secure method for non privileged users to
create and mount their own filesystem implementations.
You can download the source code releases from
http://sourceforge.net/projects/fuse
or alternatively you can use CVS to get the very latest development
version by setting the cvsroot to
:pserver:anonymous@cvs.sourceforge.net:/cvsroot/fuse
and checking out the 'fuse' module.
Installation
============
./configure
make
make install
modprobe fuse
You may also need to add '/usr/local/lib' to '/etc/ld.so.conf' and/or
run ldconfig.
For more details see the file 'INSTALL'
How To Use
==========
FUSE is made up of three main parts:
- A kernel filesystem module
- A userspace library
- A mount/unmount program
Here's how to create your very own virtual filesystem in five easy
steps (after installing FUSE):
1) Edit the file example/fusexmp.c to do whatever you want...
2) Build the fusexmp program
3) run 'example/fusexmp /mnt/fuse -d'
4) ls -al /mnt/fuse
5) Be glad
If it doesn't work out, please ask! Also see the file 'include/fuse.h' for
detailed documentation of the library interface.
Security
========
If you run 'make install', the fusermount program is installed
set-user-id to root. This is done to allow normal users to mount
their own filesystem implementations.
There must however be some limitations, in order to prevent Bad User from
doing nasty things. Currently those limitations are:
- The user can only mount on a mountpoint, for which it has write
permission
- The mountpoint is not a sticky directory which isn't owned by the
user (like /tmp usually is)
- No other user (including root) can access the contents of the mounted
filesystem.
Configuration
=============
Some options regarding mount policy can be set in the file
'/etc/fuse.conf'
Currently these options are:
mount_max = NNN
Set the maximum number of FUSE mounts allowed to non-root users.
The default is 1000.
user_allow_other
Allow non-root users to specify the 'allow_other' or 'allow_root'
mount options.
Mount options
=============
These are FUSE specific mount options that can be specified for all
filesystems:
default_permissions
By default FUSE doesn't check file access permissions, the
filesystem is free to implement it's access policy or leave it to
the underlying file access mechanism (e.g. in case of network
filesystems). This option enables permission checking, restricting
access based on file mode. This is option is usually useful
together with the 'allow_other' mount option.
allow_other
This option overrides the security measure restricting file access
to the user mounting the filesystem. This option is by default only
allowed to root, but this restriction can be removed with a
configuration option described in the previous section.
allow_root
This option is similar to 'allow_other' but file access is limited
to the user mounting the filesystem and root.
kernel_cache
This option disables flushing the cache of the file contents on
every open(). This should only be enabled on filesystems, where the
file data is never changed externally (not through the mounted FUSE
filesystem). Thus it is not suitable for network filesystems and
other "intermediate" filesystems.
NOTE: if this option is not specified (and neither 'direct_io') data
is still cached after the open(), so a read() system call will not
always initiate a read operation.
large_read
Issue large read requests. This can improve performance for some
filesystems, but can also degrade performance. This option is only
useful on 2.4.X kernels, as on 2.6 kernels requests size is
automatically determined for optimum performance.
direct_io
This option disables the use of page cache (file content cache) in
the kernel for this filesystem. This has several affects:
- Each read() or write() system call will initiate one or more
read or write operations, data will not be cached in the
kernel.
- The return value of the read() and write() system calls will
correspond to the return values of the read and write
operations. This is useful for example if the file size is not
known in advance (before reading it).
max_read=N
With this option the maximum size of read operations can be set.
The default is infinite. Note that the size of read requests is
limited anyway to 32 pages (which is 128kbyte on i386).
hard_remove
The default behavior is that if an open file is deleted, the file is
renamed to a hidden file (.fuse_hiddenXXX), and only removed when
the file is finally released. This relieves the filesystem
implementation of having to deal with this problem. This option
disables the hiding behavior, and files are removed immediately in
an unlink operation (or in a rename operation which overwrites an
existing file).
debug
Turns on debug information printing by the library.
fsname=NAME
Sets the filesystem name. The default is the program name.
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