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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 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.

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, restrict-
              ing 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  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.

       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
              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.

       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  opera-
              tions.  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 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.

       fsname=NAME
              Sets  the  filesystem source (first field in /etc/mtab). The de-
              fault 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 guaran-
              tee uniqueness, however some applications rely on this value be-
              ing 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  privi-
              leged  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_time-
              out=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  sup-
              port request interruption.

       intr_signal=NUM
              Specify which signal number to send to the filesystem when a re-
              quest 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 possi-
              ble values). Default is UTF-8.

       to_code=CHARSET
              Character set to convert to.  Default is determined by the  cur-
              rent 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 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
              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  (fuser-
       mount -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+de-
       bian@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)

NAME | DESCRIPTION | CONFIGURATION | OPTIONS | FUSE MODULES (STACKING) | SECURITY | NOTE | AUTHORS | SEE ALSO