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

NAME

       fuse - format and options for the fuse file systems

DESCRIPTION

       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.

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 (see below).

OPTIONS

       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 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.  So all users (including
	      root) can access the files.  This option is by default only allowed to root, but this restriction can be removed with  a	configura-
	      tion 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.  This option and
	      allow_other are mutually exclusive.

       kernel_cache
	      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 filesys-
	      tems 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.

       auto_cache
	      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.

       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:

       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 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).

       max_readahead=N
	      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
	      (128kbytes)

       max_write=N
	      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.

       async_read
	      Perform reads asynchronously. This is the default

       sync_read
	      Perform all reads (even read-ahead) synchronously.

       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).

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

       debug  Turns on debug information printing by the library.

       fsname=NAME
	      Sets the filesystem source (first field in /etc/mtab). The default is the mount program name.

       subtype=TYPE
	      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.

       use_ino
	      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 guarantee uniqueness,
	      however some applications rely on this value being unique for the whole filesystem.

       readdir_ino
	      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.

       nonempty
	      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.

       umask=M
	      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 privileged option. The device must be specified with the fsname=NAME option.

       entry_timeout=T
	      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_timeout=2.8)

       negative_timeout=T
	      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 disabled.

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

       ac_attr_timeout=T
	      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  support
	      request interruption.

       intr_signal=NUM
	      Specify which signal number to send to the filesystem when a request is interrupted.  The default is hardcoded to USR1.

       modules=M1[:M2...]
	      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.

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

   iconv
       Perform file name character set conversion.  Options are:

       from_code=CHARSET
	      Character set to convert from (see iconv -l for a list of possible values). Default is UTF-8.

       to_code=CHARSET
	      Character set to convert to.  Default is determined by the current locale.

   subdir
       Prepend a given directory to each path. Options are:

       subdir=DIR
	      Directory to prepend to all paths.  This option is mandatory.

       rellinks
	      Transform absolute symlinks into relative

       norellinks
	      Do not transform absolute symlinks into relative.  This is the default.

SECURITY

       The fusermount program is installed set-user-gid to fuse. This is done to allow users from fuse group to mount their own filesystem  imple-
       mentations.   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 permission

       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.

NOTE

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

AUTHORS

       The main author of FUSE is Miklos Szeredi <mszeredi@inf.bme.hu>.

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

SEE ALSO

       fusermount(1) mount(8)

																	   fuse(8)