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MOUNT_FUSEFS(8)		  BSD System Manager's Manual	       MOUNT_FUSEFS(8)

     mount_fusefs -- mount a Fuse file system daemon

     mount_fusefs [-A] [-S] [-v] [-D fuse_daemon] [-O daemon_opts]
		  [-s special] [-m node] [-h] [-V] [-o option ...] special
		  node [fuse_daemon ...]

     Basic usage is to start a fuse daemon on the given	special	file.  In
     practice, the daemon is assigned a	special	file automatically, which can
     then be identified	via fstat(1).  That special file can then be mounted
     by	mount_fusefs.

     However, the procedure of spawning	a daemon will usually be automated so
     that it is	performed by mount_fusefs.  If the command invoking a given
     fuse_daemon is appended to	the list of arguments, mount_fusefs will call
     the fuse_daemon via that command.	In that	way the	fuse_daemon will be
     instructed	to attach itself to special.  From that	on mounting goes as in
     the simple	case. (See DAEMON MOUNTS.)

     The special argument will normally	be treated as the path of the special
     file to mount.

     However, if auto is passed	as special, then mount_fusefs will look	for a
     suitable free fuse	device by itself.

     Finally, if special is an integer it will be interpreted as the number of
     the file descriptor of an already open fuse device	(used when the Fuse
     library invokes mount_fusefs.  See	DAEMON MOUNTS).

     The options are as	follows:

     -A, --reject-allow_other
	     Prohibit the allow_other mount flag.  Intended for	use in scripts
	     and the sudoers(5)	file.

     -S, --safe
	     Run in safe mode (i.e., reject invoking a filesystem daemon).

     -v	     Be	verbose.

     -D, --daemon daemon
	     Call the specified	daemon.

     -O, --daemon_opts opts
	     Add opts to the daemon's command line.

     -s, --special special
	     Use special as special.

     -m, --mountpath node
	     Mount on node.

     -h, --help
	     Show help.

     -V, --version
	     Show version information.

     -o	     Mount options are specified via -o.  The following	options	are
	     available (and also their negated versions, by prefixing them
	     with "no"):

		     Do	not apply STRICT ACCESS	POLICY.	 Only root can use
		     this option.

	     async   I/O to the	file system may	be done	asynchronously.
		     Writes may	be delayed and/or reordered.

		     Enable traditional	(file mode based) permission checking
		     in	kernel.

	     intr    Allow signals to interrupt	operations that	are blocked
		     waiting for a reply from the server.  When	this option is
		     in	use, system calls may fail with	EINTR whenever a sig-
		     nal is received.

		     Limit size	of read	requests to n.

		     Do	not refuse unmounting if there are secondary mounts.

		     Refuse shared mounting of the daemon.  This is the	de-
		     fault behaviour, to allow sharing,	expicitly use -o

		     Prefix absolute symlinks with the mountpoint.

		     Suffix fsname to the file system name as reported by
		     statfs(2).	 This option can be used to identify the file
		     system implemented	by fuse_daemon.

     Besides the above mount options, there is a set of	pseudo-mount options
     which are supported by the	Fuse library.  One can list these by passing
     -h	to a Fuse daemon.  Most	of these options only have effect on the be-
     havior of the daemon (that	is, their scope	is limited to userspace).
     However, there are	some which do require in-kernel	support.  Currently
     the options supported by the kernel are:

	     Bypass the	buffer cache system.

	     By	default	cached buffers of a given file are flushed at each
	     open(2).  This option disables this behaviour.

     Usually users do not need to use mount_fusefs directly, as	the Fuse li-
     brary enables Fuse	daemons	to invoke mount_fusefs.	 That is,

	   fuse_daemon device mountpoint

     has the same effect as

	   mount_fusefs	auto mountpoint	fuse_daemon

     This is the recommended usage when	you want basic usage (eg, run the dae-
     mon at a low privilege level but mount it as root).

     The strict	access policy for Fuse filesystems lets	one use	the filesystem
     only if the filesystem daemon has the same	credentials (uid, real uid,
     gid, real gid) as the user.

     This is applied for Fuse mounts by	default	and only root can mount	with-
     out the strict access policy (i.e., the allow_other mount option).

     This is to	shield users from the daemon "spying" on their I/O activities.

     Users might opt to	willingly relax	strict access policy (as far as	they
     are concerned) by doing their own secondary mount (See SHARED MOUNTS).

     A Fuse daemon can be shared (i.e.,	mounted	multiple times).  When doing
     the first (primary) mount,	the spawner and	the mounter of the daemon must
     have the same uid,	or the mounter should be the superuser.

     After the primary mount is	in place, secondary mounts can be done by any-
     one unless	this feature is	disabled by private.  The behaviour of a sec-
     ondary mount is analogous to that of symbolic links: they redirect	all
     filesystem	operations to the primary mount.

     Doing a secondary mount is	like signing an	agreement: by this action, the
     mounter agrees that the Fuse daemon can trace her I/O activities.	From
     then on she is not	banned from using the filesystem (either via her own
     mount or via the primary mount), regardless whether allow_other is	used
     or	not.

     The device	name of	a secondary mount is the device	name of	the corre-
     sponding primary mount, followed by a '#' character and the index of the
     secondary mount; e.g., /dev/fuse0#3.

     System administrators might want to use a custom mount policy (ie., one
     going beyond the vfs.usermount sysctl).  The primary tool for such	pur-
     poses is sudo(8).	However, given that mount_fusefs is capable of invok-
     ing an arbitrary program, one must	be careful when	doing this.
     mount_fusefs is designed in a way such that it makes that easy.  For this
     purpose, there are	options	which disable certain risky features (-S and
     -A), and command line parsing is done in a	flexible way: mixing options
     and non-options is	allowed, but processing	them stops at the third	non-
     option argument (after the	first two have been utilized as	device and
     mountpoint).  The rest of the command line	specifies the daemon and its
     arguments.	 (Alternatively, the daemon, the special and the mount path
     can be specified using the	respective options.) Note that mount_fusefs
     ignores the environment variable POSIXLY_CORRECT and always behaves as

     In	general, to be as scripting / sudoers(5) friendly as possible, no in-
     formation has a fixed position in the command line, but once a given
     piece of information is provided, subsequent arguments/options cannot
     override it (with the exception of	some non-critical ones).

     MOUNT_FUSEFS_SAFE	This has the same effect as the	-S option.

			This has the same effect as the	-v option.

			If set,	mount_fusefs will ignore uknown	mount options.

			Adjust behavior	to the needs of	the FUSE library.
			Currently it effects help output.

     Although the following variables do not have any effect on	mount_fusefs
     itself, they affect the behaviour of fuse daemons:

     FUSE_DEV_NAME  Device to attach.  If not set, the multiplexer path
		    /dev/fuse is used.

     FUSE_DEV_FD    File desciptor of an opened	Fuse device to use.  Overrides

     FUSE_NO_MOUNT  If set, the	library	will not attempt to mount the filesys-
		    tem, even if a mountpoint argument is supplied.

     /dev/fuse	Fuse device with which the kernel and Fuse daemons can commu-

     /dev/fuse	The multiplexer	path.  An open(2) performed on it automati-
		cally is passed	to a free Fuse device by the kernel (which
		might be created just for this puprose).

     Mount the example filesystem in the Fuse distribution (from its direc-
     tory): either

	   ./fusexmp /mnt/fuse


	   mount_fusefs	auto /mnt/fuse ./fusexmp

     Doing the same in two steps, using	/dev/fuse0:

	   FUSE_DEV_NAME=/dev/fuse ./fusexmp &&
	   mount_fusefs	/dev/fuse /mnt/fuse

     A script wrapper for fusexmp which	ensures	that mount_fusefs does not
     call any external utility and also	provides a hacky (non race-free) auto-
     matic device selection:

	   #!/bin/sh -e

	   FUSE_DEV_NAME=/dev/fuse fusexmp
	   mount_fusefs	-S /dev/fuse /mnt/fuse "$@"

     fstat(1), mount(8), sudo(8), umount(8)

     mount_fusefs was written as the part of the FreeBSD implementation	of the
     Fuse userspace filesystem framework (see and first appeared in the
     sysutils/fusefs-kmod port,	supporting FreeBSD 6.0.	 It was	added to the
     base system in FreeBSD 10.0.

     This user interface is FreeBSD specific.  Secondary mounts	should be un-
     mounted via their device name.  If	an attempt is made to unmount them via
     their filesystem root path, the unmount request will be forwarded to the
     primary mount path.  In general, unmounting by device name	is less	error-
     prone than	by mount path (although	the latter will	also work under	normal

     If	the daemon is specified	via the	-D and -O options, it will be invoked
     via system(3), and	the daemon's command line will also have an "&"	con-
     trol operator appended, so	that we	do not have to wait for	its termina-
     tion.  You	should use a simple command line when invoking the daemon via
     these options.

     special is	treated	as a multiplexer if and	only if	it is literally	the
     same as auto or /dev/fuse.	 Other paths which are equivalent with
     /dev/fuse (eg., /../dev/fuse) are not.

BSD				 July 31, 2019				   BSD


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