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NAME | DESCRIPTION | DEFINITIONS | CONFIGURATION | OPTIONS | FUSE MODULES (STACKING) | SECURITY | NOTE | AUTHORS | SEE ALSO | COLOPHON |
fuse(8) System Manager's Manual fuse(8)
fuse - configuration and mount options for FUSE file systems
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.
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.
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.
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.
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.
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.
FUSE filesystems are unmounted using the fusermount3(1) command
(fusermount3 -u mountpoint).
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.
fusermount3(1) fusermount(1) mount(8)
This page is part of the Libfuse (Filesystem in Userspace) project.
Information about the project can be found at
⟨https://github.com/libfuse/libfuse⟩. If you have a bug report for
this manual page, see ⟨https://github.com/libfuse/libfuse/issues⟩.
This page was obtained from the project's upstream Git repository
⟨git://git.code.sf.net/p/fuse/fuse⟩ on 2017-07-05. If you discover
any rendering problems in this HTML version of the page, or you
believe there is a better or more up-to-date source for the page, or
you have corrections or improvements to the information in this
COLOPHON (which is not part of the original manual page), send a mail
to man-pages@man7.org
fuse(8)
Pages that refer to this page: fuse2fs(1), fusermount3(1), fuse(4)