Ubuntu Manpage: fuse - format and options for the fuse file systems

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 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 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.