Provided by: fuse3_3.4.1-1_amd64 bug

NAME

       fuse - configuration and mount options for 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.

DEFINITIONS

       FUSE   The in-kernel filesystem that forwards requests to a user-space process.

       filesystem
              The user-space process that responds to requests received from the kernel.

       libfuse
              The  shared library that most (user-space) filesystems use to communicate with FUSE
              (the kernel filesystem). libfuse also provides the fusermount3  (or  fusermount  if
              you  have  older  version of libfuse) helper to allow non-privileged users to mount
              filesystems.

       filesystem owner
              The user that starts the filesystem and instructs the kernel to associate it with a
              particular  mountpoint.  The  latter  is typically done by the filesystem itself on
              start-up. When using libfuse, this is done by calling the fusermount3 utility.

       client Any process that interacts with the mountpoint.

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).

       These limits are enforced by the fusermount3 helper, so they can be avoided by filesystems
       that run as root.

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
              This option instructs the kernel to perform its own  permission  check  instead  of
              deferring  all  permission  checking  to the filesystem. The check by the kernel is
              done in addition to any permission checks by  the  filesystem,  and  both  have  to
              succeed  for  an  operation  to  be  allowed.  The  kernel performs a standard UNIX
              permission check (based on mode bits and ownership  of  the  directory  entry,  and
              uid/gid of the client).

              This  mount  option  is  activated implicitly if the filesystem enables ACL support
              during the initial feature negotiation when opening the device fd.  In  this  case,
              the kernel performs both ACL and standard unix permission checking.

              Filesystems that do not implement any permission checking should generally add this
              option internally.

       allow_other
              This  option  overrides  the  security  measure  restricting  file  access  to  the
              filesystem owner, so that all users (including root) can access the files.

       rootmode=M
              Specifies the the file mode of the filesystem's root (in octal representation).

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

       blksize=N
              Set the block size for the filesystem. This option is only valid for 'fuseblk' type
              mounts. The default is 512.

              In  most cases, this option should not be specified by the filesystem owner but set
              internally by the filesystem.

       max_read=N
              With this option the maximum size of read operations can be  set.  The  default  is
              infinite,  but typically the kernel enforces its own limit in addition to this one.
              A value of zero corresponds to no limit.

              This option should not be specified  by  the  filesystem  owner.  The  correct  (or
              optimum)  value  depends on the filesystem implementation and should thus be set by
              the filesystem internally.

              This mount option is deprecated in favor of direct negotiation over the  device  fd
              (as  done  for  e.g.  the  maximum  size  of write operations). For the time being,
              libfuse-using filesystems that want to limit the read size must therefore use  this
              mount option and set the same value again in the init() handler.

       fd=N   The  file  descriptor to use for communication between the userspace filesystem and
              the kernel.  The file descriptor must have been obtained by opening the FUSE device
              (/dev/fuse).

              This  option  should not be specified by the filesystem owner. It is set by libfuse
              (or, if libfuse is not used, must be set by the filesystem itself).

       user_id=N
              group_id=N Specifies the numeric uid/gid of the mount owner.

              This option should not be specified by the filesystem owner. It is set  by  libfuse
              (or, if libfuse is not used, must be set by the filesystem itself).

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

       subtype=TYPE
              Sets the filesystem type (third field in /etc/mtab). The default is the name of the
              filesystem  process.  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.

   libfuse-specific mount options:
       These  following options are not actually passed to the kernel but interpreted by libfuse.
       They can be specified for all filesystems that use libfuse:

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

       auto_unmount
              This  option  enables  automatic release of the mountpoint if filesystem terminates
              for  any  reason.  Normally  the  filesystem  is  responsible  for  releasing   the
              mountpoint,  which means that the mountpoint becomes inaccessible if the filesystem
              terminates without first unmounting.

              At the moment, this option implies that the filesystem will also  be  mounted  with
              nodev and nosuid (even when mounted by root). This restriction may be lifted in the
              future.

   High-level mount options:
       These following options are not actually passed to the kernel but interpreted by  libfuse.
       They can only be specified for filesystems that use the high-level libfuse API:

       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 is an alternative to kernel_cache. Instead of  unconditionally  keeping
              cached  data, the cached data is invalidated on open(2) if the modification time or
              the size of the file has changed since it was last opened.

       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).

       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

       noforget

       remember=T
              Normally, libfuse assigns inodes to paths only for as long as the kernel  is  aware
              of  them.  With this option inodes are instead assigned for at least T seconds (or,
              in the case of noforget, the life-time of the filesystem). This will  require  more
              memory,  but  may  be  necessary  when  using  applications  that make use of inode
              numbers.

       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.

   mount.fuse3 options:
       These  options  are interpreted by mount.fuse3 and are thus only available when mounting a
       file system via mount.fuse3 (such as when mounting via the  generic  mount(1)  command  or
       /etc/fstab). Supported options are:

       setuid=USER
              Switch to USER and its primary group before launching the FUSE file system process.
              mount.fuse3 must be run as root or with CAP_SETUID and CAP_SETGID for this to work.

       drop_privileges
              Perform setup of the FUSE file descriptor  and  mounting  the  file  system  before
              launching  the  FUSE  file system process. mount.fuse3 requires privilege to do so,
              i.e. must be run as root or at least with CAP_SYS_ADMIN and  CAP_SETPCAP.  It  will
              launch the file system process fully unprivileged, i.e. without capabilities(7) and
              prctl(2) flags set up such that privileges can't be reacquired (e.g. via setuid  or
              fscaps  binaries).  This  reduces risk in the event of the FUSE file system process
              getting compromised by malicious file system data.

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 fusermount3 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  fusermount3(1)  command   (fusermount3   -u
       mountpoint).

AUTHORS

       FUSE is currently maintained by Nikolaus Rath <Nikolaus@rath.org>

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

       This      man     page     was     originally     written     by     Bastien     Roucaries
       <roucaries.bastien+debian@gmail.com> for the Debian GNU/Linux distribution.

SEE ALSO

       fusermount3(1) fusermount(1) mount(8)

                                                                                          fuse(8)