Provided by: bindfs_1.13.7-1_amd64 
NAME
bindfs ‐ mount --bind in user-space
SYNOPSIS
bindfs [options] dir mountpoint
DESCRIPTION
A FUSE filesystem for mirroring the contents of a directory to another directory. Additionally, one can
change the permissions of files in the mirrored directory.
FILE OWNERSHIP
-u, --force-user, -o force-user=...
Makes all files owned by the specified user. Also causes chown on the mounted filesystem to
always fail.
-g, --force-group=group, -o force-group=...
Makes all files owned by the specified group. Also causes chgrp on the mounted filesystem to
always fail.
-p, --perms=permissions, -o perms=...
Takes a comma- or colon-separated list of chmod-like permission specifications to be applied to
the permission bits in order. See PERMISSION SPECIFICATION below for details.
This only affects how the permission bits of existing files are altered when shown in the mounted
directory. You can use --create-with-perms to change the permissions that newly created files get
in the source directory.
Note that, as usual, the root user isn't bound by the permissions set here. You can get a truly
read-only mount by using -r.
-m, --mirror=user1:user2:..., -o mirror=...
Takes a comma- or colon-separated list of users who will see themselves as the owners of all
files. Users who are not listed here will still be able to access the mount if the permissions
otherwise allow them to.
You can also give a group name prefixed with an '@' to mirror all members of a group. This will
not change which group the files are shown to have.
-M, --mirror-only=user1:user2:..., -o mirror-only=...
Like --mirror but disallows access for all other users (except root).
--map=user1/user2:@group1/@group2:..., -o map=...
Given a mapping user1/user2, all files owned by user1 are shown as owned by user2. When user2
creates files, they are chowned to user1 in the underlying directory. When files are chowned to
user2, they are chowned to user1 in the underlying directory. Works similarly for groups.
A single user or group may appear no more than once on the left and once on the right of a slash
in the list of mappings. Currently, the options --force-user, --force-group, --mirror, --create-
for-*, --chown-* and --chgrp-* override the corresponding behavior of this option.
Requires mounting as root.
--uid-offset=..., -o uid-offset=...
Works like --map, but adds the given number to all file owner user IDs. For instance, --uid-
offset=100000 causes a file owned by user 123 to be shown as owned by user 100123.
For now, this option cannot be used together with --map. Please file an issue with the desired
semantics if you have a case for using them together.
Requires mounting as root.
--gid-offset=..., -o gid-offset=...
Works exactly like --uid-offset but for groups.
FILE CREATION POLICY
New files and directories are created so they are owned by the mounter. bindfs can let this happen (the
default for normal users), or it can try to change the owner to the uid/gid of the process that wants to
create the file (the default for root). It is also possible to have bindfs try to change the owner to a
particular user or group.
--create-as-user, -o create-as-user
Tries to change the owner and group of new files and directories to the uid and gid of the caller.
This can work only if the mounter is root. It is also the default behavior (mimicing mount
--bind) if the mounter is root.
--create-as-mounter, -o create-as-mounter
All new files and directories will be owned by the mounter. This is the default behavior for
non-root mounters.
--create-for-user=user, -o create-for-user=...
Tries to change the owner of new files and directories to the user specified here. This can work
only if the mounter is root. This option overrides the --create-as-user and --create-as-mounter
options.
--create-for-group=group, -o create-for-group=...
Tries to change the owning group of new files and directories to the group specified here. This
can work only if the mounter is root. This option overrides the --create-as-user and
--create-as-mounter options.
--create-with-perms=permissions, -o create-with-perms=...
Works like --perms but is applied to the permission bits of new files get in the source directory.
Normally the permissions of new files depend on the creating process's preferences and umask.
This option can be used to modify those permissions or override them completely. See PERMISSION
SPECIFICATION below for details.
CHOWN/CHGRP POLICY
The behaviour on chown/chgrp calls can be changed. By default they are passed through to the source
directory even if bindfs is set to show a fake owner/group. A chown/chgrp call will only succeed if the
user has enough mirrored permissions to chmod the mirrored file AND the mounter has enough permissions to
chmod the real file.
--chown-normal, -o chown-normal
Tries to chown the underlying file. This is the default.
--chown-ignore, -o chown-ignore
Lets chown succeed (if the user has enough mirrored permissions) but actually does nothing. A
combined chown/chgrp is effectively turned into a chgrp-only request.
--chown-deny, -o chown-deny
Makes chown always fail with a 'permission denied' error. A combined chown/chgrp request will
fail as well.
--chgrp-normal, -o chgrp-normal
Tries to chgrp the underlying file. This is the default.
--chgrp-ignore, -o chgrp-ignore
Lets chgrp succeed (if the user has enough mirrored permissions) but actually does nothing. A
combined chown/chgrp is effectively turned into a chown-only request.
--chgrp-deny, -o chgrp-deny
Makes chgrp always fail with a 'permission denied' error. A combined chown/chgrp request will
fail as well.
CHMOD POLICY
Chmod calls are forwarded to the source directory by default. This may cause unexpected behaviour if
bindfs is altering permission bits.
--chmod-normal, -o chmod-normal
Tries to chmod the underlying file. This will succeed if the user has the appropriate mirrored
permissions to chmod the mirrored file AND the mounter has enough permissions to chmod the real
file. This is the default (in order to behave like mount --bind by default).
--chmod-ignore, -o chmod-ignore
Lets chmod succeed (if the user has enough mirrored permissions) but actually does nothing.
--chmod-deny, -o chmod-deny
Makes chmod always fail with a 'permission denied' error.
--chmod-filter=permissions, -o chmod-filter=...
Changes the permission bits of a chmod request before it is applied to the original file. Accepts
the same permission syntax as --perms. See PERMISSION SPECIFICATION below for details.
--chmod-allow-x, -o chmod-allow-x
Allows setting and clearing the executable attribute on files (but not directories). When used
with --chmod-ignore, chmods will only affect execute bits on files and changes to other bits are
discarded. With --chmod-deny, all chmods that would change any bits except excecute bits on files
will still fail with a 'permission denied'. This option does nothing with --chmod-normal.
XATTR POLICY
Extended attributes are mirrored by default, though not all underlying file systems support xattrs.
--xattr-none, -o xattr-none
Disable extended attributes altogether. All operations will return 'Operation not supported'.
--xattr-ro, -o xattr-ro
Let extended attributes be read-only.
--xattr-rw, -o xattr-rw
Let extended attributes be read-write (the default). The read/write permissions are checked
against the (possibly modified) file permissions inside the mount.
RATE LIMITS
Reads and writes through the mount point can be throttled. Throttling works by sleeping the required
amount of time on each read or write request. Throttling imposes one global limit on all readers/writers
as opposed to a per-process or per-user limit.
Currently, the implementation is not entirely fair. See BUGS below.
--read-rate=N, -o read-rate=N
Allow at most N bytes per second to be read. N may have one of the following (1024-based)
suffixes: k, M, G, T.
--write-rate=N, -o write-rate=N
Same as above, but for writes.
LINK HANDLING
--hide-hard-links, -o hide-hard-links
Shows the hard link count of all files as 1.
--resolve-symlinks, -o resolve-symlinks
Transparently resolves symbolic links. Disables creation of new symbolic links.
With the following exceptions, operations will operate directly on the target file instead of the
symlink. Renaming/moving a resolved symlink (inside the same mount point) will move the symlink
instead of the underlying file. Deleting a resolved symlink will delete the underlying symlink but
not the destination file. This can be configured with --resolved-symlink-deletion.
Note that when some programs, such as vim, save files, they actually move the old file out of the
way, create a new file in its place, and finally delete the old file. Doing these operations on a
resolved symlink will replace it with a regular file.
Symlinks pointing outside the source directory are supported with the following exception:
accessing the mountpoint recursively through a resolved symlink is not supported and will return
an error. This is because a FUSE filesystem cannot reliably call itself recursively without
deadlocking, especially in single-threaded mode.
--resolved-symlink-deletion=policy, -o resolved-symlink-deletion=policy
If --resolve-symlinks is enabled, decides what happens when a resolved symlink is deleted. The
options are: deny (resolved symlinks cannot be deleted), symlink-only (the underlying symlink is
deleted, its target is not), symlink-first (the symlink is deleted, and if that succeeds, the
target is deleted but no error is reported if that fails) or target-first (the target is deleted
first, and the symlink is deleted only if deleting the target succeeded). The default is symlink-
only.
Note that deleting files inside symlinked directories is always possible with all settings,
including deny, unless something else protects those files.
--block-devices-as-files, -o block-devices-as-files
Shows block devices as regular files.
MISCELLANEOUS OPTIONS
-h, --help
Displays a help message and exits.
-V, --version
Displays version information and exits.
--no-allow-other, -o no-allow-other
Does not add -o allow_other to FUSE options. This causes the mount to be accessible only by the
current user.
(The deprecated shorthand -n is also still accepted.)
--realistic-permissions, -o realistic-permissions
Hides read/write/execute permissions for a mirrored file when the mounter doesn't have
read/write/execute access to the underlying file. Useless when mounting as root, since root will
always have full access.
(Prior to version 1.10 this option was the default behavior. I felt it violated the principle of
least surprise badly enough to warrant a small break in backwards-compatibility.)
--ctime-from-mtime, -o ctime-from-mtime
Recall that a unix file has three standard timestamps: atime (last access i.e. read time), mtime
(last content modification time) ctime (last content or metadata (inode) change time)
With this option, the ctime of each file and directory is read from its mtime. In other words,
only content modifications (as opposed to metadata changes) will be reflected in a mirrored file's
ctime. The underlying file's ctime will still be updated normally.
--enable-lock-forwarding, -o enable-lock-forwarding
Forwards flock and fcntl locking requests to the source directory. This way, locking a file in
the bindfs mount will also lock the file in the source directory.
This option must be used with --multithreaded because otherwise bindfs will deadlock as soon as
there is lock contention. However, see BUGS below for caveats about --multithreaded with the
current implementation.
--disable-lock-forwarding, -o disable-lock-forwarding
Currently does nothing, but a future release may default to enabling lock forwarding. If you
depend on this behaviour, it's recommended to set this flag explicitly.
--enable-ioctl, -o enable-ioctl
Enables forwarding of ioctl, which is needed for some advanced features such as append-only files
(chattr +a). Note that the ioctl action will be performed as the mounter, not the calling user. No
efforts are made to check whether the calling user would ordinarily have the permissions to make
the ioctl. This may be a security concern, especially when mounting as root.
--multithreaded, -o multithreaded
Run bindfs in multithreaded mode. While bindfs is designed to be otherwise thread-safe, there is
currently a race condition that may pose a security risk for some use cases. See BUGS below.
FUSE OPTIONS
-o options
Fuse options.
-r, -o ro
Make the mount strictly read-only. This even prevents root from writing to it. If this is all
you need, then (since Linux 2.6.26) you can get a more efficent mount with mount --bind and then
mount -o remount,ro.
-d, -o debug
Enable debug output (implies -f).
-f Foreground operation.
PERMISSION SPECIFICATION
The -p option takes a comma- or colon-separated list of either octal numeric permission bits or symbolic
representations of permission bit operations. The symbolic representation is based on that of the
chmod(1) command. setuid, setgid and sticky bits are ignored.
This program extends the chmod symbolic representation with the following operands:
`D' (right hand side)
Works like X but applies only to directories (not to executables).
`d' and `f' (left hand side)
Makes this directive only apply to directories (d) or files (f).
e.g. gd-w would remove the group write bit from all directories.
`u', `g', `o' (right hand side)
Uses the user (u), group (g) or others (o) permission bits of
the original file.
e.g. g=u would copy the user's permission bits to the group.
ug+o would add the others' permissions to the owner and group.
Examples
o-rwx Removes all permission bits from others.
g=rD Allows group to read all files and enter all directories, but nothing else.
0644,a+X
Sets permission bits to 0644 and adds the execute bit for everyone to all directories and
executables.
og-x:og+rD:u=rwX:g+rw
Removes execute bit for others and group, adds read and directory execute for others and group,
sets user permissions to read, write and execute directory/executable, adds read and write for
group.
EXAMPLES
bindfs -u www -g nogroup -p 0000,u=rD ~/mywebsite ~/public_html/mysite
Publishes a website in public_html so that only the 'www' user can read the site.
bindfs -M foo,bar,1007,@mygroup -p 0600,u+X dir mnt
Gives access to 'foo', 'bar', the user with the UID 1007 as well as everyone in the group
'mygroup'. Sets the permission bits to 0600, thus giving the specified users read/write access,
and adds the user execute bit for directories and executables.
bindfs -ono-allow-other,perms=a-w somedir somedir
Makes a directory read-only and accessable only by the current user.
/home/bob/shared /var/www/shared/bob fuse.bindfs perms=0000:u+rD 0 0
An example /etc/fstab entry. Note that the colon must be used to separate arguments to perms,
because the comma is an option separator in /etc/fstab.
bindfs#/home/bob/shared /var/www/shared/bob fuse perms=0000:u+rD 0 0
Older systems may require this deprecated fstab syntax.
NOTES
Setuid and setgid bits have no effect inside the mount. This is a necessary security feature of FUSE.
Access to device files is denied by default by FUSE as a security precaution. Use -o dev to enable
access (requires mounting as root). This may not be supported on all operating systems.
MacFuse caches file contents by default. This means that changes in source files are not always
immediately visible under the mount point. -o nolocalcaches can be used to disable the cache.
When using --mirror[-only] @somegroup, bindfs won't see changes to the group's member list. Sending
bindfs a SIGUSR1 signal will make it reread the user database.
The following extra options may be useful under osxfuse: -o
local,allow_other,extended_security,noappledouble See https://github.com/osxfuse/osxfuse/wiki/Mount-
options for details.
BUGS
If bindfs is run in multithreaded mode (with the --multithreaded option) then it's possible for another
process to briefly see a file with an incorrect owner, group or permissions. This may constitute a
security risk if you rely on bindfs to reduce permissions on new files. For this reason, as of version
1.11 bindfs runs in single-threaded mode by default.
Rate limiting favors the process with the larger block size. If two processes compete for read/write
access, the one whose read()/write() calls specify the larger block size gets to read/write faster. The
total rate limit is maintained though, and clients with equal block sizes and a similar rate of requests
are treated fairly as long as the kernel orders their requests fairly.
Some features relying on xattrs might not work properly on OS X
(https://github.com/mpartel/bindfs/issues/21). For instance, Finder tags seem to work but comments might
not.
Please report bugs and/or send pull requests to https://github.com/mpartel/bindfs/issues.
DEPRECATIONS
The option names --user and --group were deprecated and replaced with --force-user and --force-group in
version 1.12. The former names clashed with standard option names. They are still available but their
use is discouraged and prints a warning. The synonym --owner is also deprecated for consistency.
AUTHOR
Martin Pärtel <martin dot partel at gmail dot com>
SEE ALSO
chmod(1), fusermount(1), http://bindfs.org/ BINDFS(1)