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fuse(8)			    System Manager's Manual		       fuse(8)

       fuse - format and options for the fuse file systems

       FUSE (Filesystem	in Userspace) is a simple interface for	userspace pro-
       grams 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.

       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.

	      Allow non-root users to specify the  allow_other	or  allow_root
	      mount options (see below).

       Most of the generic mount options described in mount are	supported (ro,
       rw, suid, nosuid, dev,  nodev,  exec,  noexec,  atime,  noatime,	 sync,
       async,  dirsync). Filesystems are mounted with nodev,nosuid by default,
       which can only be overridden by a privileged user.

   General mount options:
       These are FUSE specific mount options that can  be  specified  for  all

	      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, restrict-
	      ing access based on file mode.  This is option is	usually	useful
	      together with the	allow_other mount option.

	      This option overrides the	security measure restricting file  ac-
	      cess to the user mounting	the filesystem.	 So all	users (includ-
	      ing root)	can access the files.  This option is by default  only
	      allowed to root, but this	restriction can	be removed with	a con-
	      figuration option	described in the previous section.

	      This option is similar to	allow_other but	file access is limited
	      to  the  user mounting the filesystem and	root.  This option and
	      allow_other are mutually exclusive.

	      This option disables flushing the	cache of the file contents  on
	      every  open(2).	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(2), so a read(2) system call
	      will not always initiate a read operation.

	      This option enables automatic flushing  of  the  data  cache  on
	      open(2). The cache will only be flushed if the modification time
	      or the size of the file has changed.

	      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.

	      This  option disables the	use of page cache (file	content	cache)
	      in the kernel for	this filesystem. This has several affects:

       1.     Each read(2) or write(2) system call will	initiate one  or  more
	      read or write operations,	data will not be cached	in the kernel.

       2.     The  return  value  of  the read() and write() system calls will
	      correspond to the	return values of the  read  and	 write	opera-
	      tions.  This is useful for example if the	file size is not known
	      in advance (before reading it).

	      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).

	      Set the maximum number of	bytes to read-ahead.  The  default  is
	      determined by the	kernel.	On linux-2.6.22	or earlier it's	131072

	      Set the maximum number of	bytes in a single write	operation. The
	      default  is  128kbytes.	Note, that due to various limitations,
	      the size of write	requests can be	much smaller  (4kbytes).  This
	      limitation will be removed in the	future.

	      Perform reads asynchronously. This is the	default

	      Perform all reads	(even read-ahead) synchronously.

	      The  default  behavior  is  that if an open file is deleted, the
	      file is renamed to a hidden file (.fuse_hiddenXXX), and only re-
	      moved  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).

	      It  is recommended that you not use the hard_remove option. When
	      hard_remove is set, the following	libc  functions	 fail  on  un-
	      linked  files  (returning	 errno	of ENOENT): read(2), write(2),
	      fsync(2),	close(2),  f*xattr(2),	ftruncate(2),  fstat(2),  fch-
	      mod(2), fchown(2)

       debug  Turns on debug information printing by the library.

	      Sets  the	 filesystem source (first field	in /etc/mtab). The de-
	      fault is the mount program name.

	      Sets the filesystem type (third field in /etc/mtab). The default
	      is the mount program name. If the	kernel suppports it, /etc/mtab
	      and /proc/mounts will show the filesystem	type as	fuse.TYPE

	      If the kernel doesn't support subtypes, the source filed will be
	      TYPE#NAME, or if fsname option is	not specified, just TYPE.

	      Honor  the  st_ino  field	 in  kernel  functions	getattr()  and
	      fill_dir(). This value is	used to	fill in	the  st_ino  field  in
	      the stat(2), lstat(2), fstat(2) functions	and the	d_ino field in
	      the readdir(2) function. The filesystem does not have to guaran-
	      tee uniqueness, however some applications	rely on	this value be-
	      ing unique for the whole filesystem.

	      If use_ino option	is not given, still try	to fill	in  the	 d_ino
	      field  in	 readdir(2). If	the name was previously	looked up, and
	      is still in the cache, the inode	number	found  there  will  be
	      used.  Otherwise	it  will  be  set to -1.  If use_ino option is
	      given, this option is ignored.

	      Allows mounts over a non-empty file  or  directory.  By  default
	      these   mounts are rejected to prevent accidental	covering up of
	      data, which could	for example prevent automatic backup.

	      Override the permission bits in st_mode set by  the  filesystem.
	      The  resulting  permission  bits	are  the ones missing from the
	      given umask value.  The value is given in	octal representation.

       uid=N  Override the st_uid field	set by the filesystem (N is numeric).

       gid=N  Override the st_gid field	set by the filesystem (N is numeric).

       blkdev Mount a filesystem backed	by a block device.  This is  a	privi-
	      leged  option. The device	must be	specified with the fsname=NAME

	      The timeout in seconds for which name lookups  will  be  cached.
	      The  default  is	1.0 second. For	all the	timeout	options, it is
	      possible to give fractions of a second as	well (e.g. entry_time-

	      The  timeout  in	seconds	 for  which  a negative	lookup will be
	      cached. This means, that if file did not exist  (lookup  retuned
	      ENOENT),	the  lookup will only be redone	after the timeout, and
	      the file/directory will be assumed to not	exist until then.  The
	      default is 0.0 second, meaning that caching negative lookups are

	      The timeout in seconds for which file/directory  attributes  are
	      cached.  The default is 1.0 second.

	      The  timeout in seconds for which	file attributes	are cached for
	      the purpose of checking if auto_cache should flush the file data
	      on  open.	The default is the value of attr_timeout

       intr   Allow  requests  to  be interrupted.  Turning on this option may
	      result in	unexpected behavior, if	the filesystem does  not  sup-
	      port request interruption.

	      Specify which signal number to send to the filesystem when a re-
	      quest is interrupted.  The default is hardcoded to USR1.

	      Add modules to the filesystem stack.  Modules are	pushed in  the
	      order  they are specified, with the original filesystem being on
	      the bottom of the	stack.

       Modules are filesystem stacking support to high level  API.  Filesystem
       modules can be built into libfuse or loaded from	shared object

       Perform file name character set conversion.  Options are:

	      Character	set to convert from (see iconv -l for a	list of	possi-
	      ble values). Default is UTF-8.

	      Character	set to convert to.  Default is determined by the  cur-
	      rent locale.

       Prepend a given directory to each path. Options are:

	      Directory	to prepend to all paths.  This option is mandatory.

	      Transform	absolute symlinks into relative

	      Do  not  transform absolute symlinks into	relative.  This	is the

       The fusermount program is installed set-user-gid	to fuse. This is  done
       to  allow users from fuse group to mount	their own filesystem implemen-
       tations.	 There must however be some limitations, in order  to  prevent
       Bad User	from doing nasty things.  Currently those limitations are:

       1.     The  user	can only mount on a mountpoint,	for which it has write

       2.     The mountpoint is	not a sticky directory which  isn't  owned  by
	      the user (like /tmp usually is)

       3.     No  other	 user  (including root)	can access the contents	of the
	      mounted filesystem.

       FUSE filesystems	are unmounted using the	fusermount(1) command  (fuser-
       mount -u	mountpoint).

       The main	author of FUSE is Miklos Szeredi <>.

       This  man  page was written by Bastien Roucaries	<roucaries.bastien+de-> for the Debian GNU/Linux	distribution (but  it  may  be
       used by others) from README file.

       fusermount(1) mount(8)



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