mount.fuse

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 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.  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
              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 supports 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
       implementations.  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)