path: root/sshfs.rst

=======
 SSHFS
=======

---------------------------------------------
 filesystem client based on SSH
---------------------------------------------

:Manual section: 1
:Manual group: User Commands

Synopsis
========

To mount a filesystem::

   sshfs [user@]host:[dir] mountpoint [options]

If *host* is a numeric IPv6 address, it needs to be enclosed in square
brackets.

To unmount it::

  fusermount3 -u mountpoint   # Linux
  umount mountpoint           # OS X, FreeBSD

Description
===========

SSHFS allows you to mount a remote filesystem using SSH (more precisely, the SFTP
subsystem). Most SSH servers support and enable this SFTP access by default, so SSHFS is
very simple to use - there's nothing to do on the server-side.

By default, file permissions are ignored by SSHFS. Any user that can access the filesystem
will be able to perform any operation that the remote server permits - based on the
credentials that were used to connect to the server. If this is undesired, local
permission checking can be enabled with ``-o default_permissions``.

By default, only the mounting user will be able to access the filesystem. Access for other
users can be enabled by passing ``-o allow_other``. In this case you most likely also
want to use ``-o default_permissions``.

It is recommended to run SSHFS as regular user (not as root).  For this to work the
mountpoint must be owned by the user.  If username is omitted SSHFS will use the local
username. If the directory is omitted, SSHFS will mount the (remote) home directory.  If
you need to enter a password sshfs will ask for it (actually it just runs ssh which ask
for the password if needed).


Options
=======


-o opt,[opt...]
   mount options, see below for details. A a variety of SSH options can
   be given here as well, see the manual pages for *sftp(1)* and
   *ssh_config(5)*.

-h, --help
   print help and exit.

-V, --version
   print version information and exit.

-d, --debug
   print debugging information.

-p PORT
   equivalent to '-o port=PORT'

-f
   do not daemonize, stay in foreground.

-s
   Single threaded operation.

-C
   equivalent to '-o compression=yes'

-F ssh_configfile
   specifies alternative ssh configuration file

-1
   equivalent to '-o ssh_protocol=1'

-o reconnect
   automatically reconnect to server if connection is
   interrupted. Attempts to access files that were opened before the
   reconnection will give errors and need to be re-opened.

-o delay_connect
   Don't immediately connect to server, wait until mountpoint is first
   accessed.

-o sshfs_sync
   synchronous writes. This will slow things down, but may be useful
   in some situations.

-o no_readahead
   Only read exactly the data that was requested, instead of
   speculatively reading more to anticipate the next read request.

-o sync_readdir
   synchronous readdir. This will slow things down, but may be useful
   in some situations.

-o workaround=LIST
   Enable the specified workaround. See the `Caveats` section below
   for some additional information. Possible values are:

   :rename: Emulate overwriting an existing file by deleting and
        renaming.
   :renamexdev: Make rename fail with EXDEV instead of the default EPERM
        to allow moving files across remote filesystems.
   :truncate: Work around servers that don't support truncate by
        coping the whole file, truncating it locally, and sending it
        back.
   :fstat: Work around broken servers that don't support *fstat()* by
           using *stat* instead.
   :buflimit: Work around OpenSSH "buffer fillup" bug.
   :createmode: Work around broken servers that produce an error when passing a
                non-zero mode to create, by always passing a mode of 0.

-o idmap=TYPE
   How to map remote UID/GIDs to local values. Possible values are:

   :none: no translation of the ID space (default).

   :user: map the UID/GID of the remote user to UID/GID of the
            mounting user.

   :file: translate UIDs/GIDs based upon the contents of `--uidfile`
            and `--gidfile`.

-o uidfile=FILE
   file containing ``username:uid`` mappings for `-o idmap=file`

-o gidfile=FILE
   file containing ``groupname:gid`` mappings for `-o idmap=file`

-o nomap=TYPE
   with idmap=file, how to handle missing mappings:

   :ignore: don't do any re-mapping
   :error:  return an error (default)

-o ssh_command=CMD
   execute CMD instead of 'ssh'

-o ssh_protocol=N
   ssh protocol to use (default: 2)

-o sftp_server=SERV
   path to sftp server or subsystem (default: sftp)

-o directport=PORT
   directly connect to PORT bypassing ssh

-o slave
   communicate over stdin and stdout bypassing network

-o disable_hardlink
   With this option set, attempts to call `link(2)` will fail with
   error code ENOSYS.

-o transform_symlinks
   transform absolute symlinks on remote side to relative
   symlinks. This means that if e.g. on the server side
   ``/foo/bar/com`` is a symlink to ``/foo/blub``, SSHFS will
   transform the link target to ``../blub`` on the client side.

-o follow_symlinks
   follow symlinks on the server, i.e. present them as regular
   files on the client. If a symlink is dangling (i.e, the target does
   not exist) the behavior depends on the remote server - the entry
   may appear as a symlink on the client, or it may appear as a
   regular file that cannot be accessed.

-o no_check_root
   don't check for existence of 'dir' on server

-o password_stdin
   read password from stdin (only for pam_mount!)

-o dir_cache=BOOL
   Enables (*yes*) or disables (*no*) the SSHFS directory cache.  The
   directory cache holds the names of directory entries. Enabling it
   allows `readdir(3)` system calls to be processed without network
   access.
   
-o dcache_max_size=N
   sets the maximum size of the directory cache.
   
-o dcache_timeout=N
   sets timeout for directory cache in seconds.
   
-o dcache_{stat,link,dir}_timeout=N
   sets separate timeout for {attributes, symlinks, names} in  the
   directory cache.
   
-o dcache_clean_interval=N
   sets the interval for automatic cleaning of the directory cache.

-o dcache_min_clean_interval=N
   sets the interval for forced cleaning of the directory cache
   when full.

-o 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() or write() 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).
      e.g. /proc filesystem 

-o max_conns=N
   sets the maximum number of simultaneous SSH connections
   to use. Each connection is established with a separate SSH process.
   The primary purpose of this feature is to improve the responsiveness of the
   file system during large file transfers. When using more than once
   connection, the *password_stdin* and *slave* options can not be
   used, and the *buflimit* workaround is not supported/

In addition, SSHFS accepts several options common to all FUSE file
systems. These are described in the `mount.fuse` manpage (look
for "general", "libfuse specific", and "high-level API" options).

Caveats / Workarounds
=====================

Hardlinks
~~~~~~~~~

If the SSH server supports the *hardlinks* extension, SSHFS will allow
you to create hardlinks. However, hardlinks will always appear as
individual files when seen through an SSHFS mount, i.e. they will
appear to have different inodes and an *st_nlink* value of 1.


Rename
~~~~~~

Some SSH servers do not support atomically overwriting the destination
when renaming a file. In this case you will get an error when you
attempt to rename a file and the destination already exists. A
workaround is to first remove the destination file, and then do the
rename. SSHFS can do this automatically if you call it with `-o
workaround=rename`. However, in this case it is still possible that
someone (or something) recreates the destination file after SSHFS has
removed it, but before SSHFS had the time to rename the old file. In
this case, the rename will still fail.


Permission denied when moving files across remote filesystems
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

Most SFTP servers return only a generic "failure" when failing to rename
across filesystem boundaries (EXDEV).  sshfs normally converts this generic
failure to a permission denied error (EPERM).  If the option ``-o
workaround=renamexdev`` is given, generic failures will be considered EXDEV
errors which will make programs like `mv(1)` attempt to actually move the
file after the failed rename.


SSHFS hangs for no apparent reason
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

In some cases, attempts to access the SSHFS mountpoint may freeze if
no filesystem activity has occured for some time. This is typically
caused by the SSH connection being dropped because of inactivity
without SSHFS being informed about that. As a workaround, you can try
to mount with ``-o ServerAliveInterval=15``. This will force the SSH
connection to stay alive even if you have no activity.


SSHFS hangs after the connection was interrupted
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

By default, network operations in SSHFS run without timeouts, mirroring the
default behavior of SSH itself. As a consequence, if the connection to the
remote host is interrupted (e.g. because a network cable was removed),
operations on files or directories under the mountpoint will block until the
connection is either restored or closed altogether (e.g. manually).
Applications that try to access such files or directories will generally appear
to "freeze" when this happens.

If it is acceptable to discard data being read or written, a quick workaround
is to kill the responsible ``sshfs`` process, which will make any blocking
operations on the mounted filesystem error out and thereby "unfreeze" the
relevant applications. Note that force unmounting with ``fusermount -zu``, on
the other hand, does not help in this case and will leave read/write operations
in the blocking state.

For a more automatic solution, one can use the ``-o ServerAliveInterval=15``
option mentioned above, which will drop the connection after not receiving a
response for 3 * 15 = 45 seconds from the remote host. By also supplying ``-o
reconnect``, one can ensure that the connection is re-established as soon as
possible afterwards. As before, this will naturally lead to loss of data that
was in the process of being read or written at the time when the connection was
interrupted.


Mounting from /etc/fstab
========================

To mount an SSHFS filesystem from ``/etc/fstab``, simply use ``sshfs`
as the file system type. (For backwards compatibility, you may also
use ``fuse.sshfs``).


See also
========

The `mount.fuse(8)` manpage.

Getting Help
============

If you need help, please ask on the <fuse-sshfs@lists.sourceforge.net>
mailing list (subscribe at
https://lists.sourceforge.net/lists/listinfo/fuse-sshfs).

Please report any bugs on the GitHub issue tracker at
https://github.com/libfuse/libfuse/issues.


Authors
=======

SSHFS is currently maintained by Nikolaus Rath <Nikolaus@rath.org>,
and was created by Miklos Szeredi <miklos@szeredi.hu>.

This man page was originally written by Bartosz Fenski
<fenio@debian.org> for the Debian GNU/Linux distribution (but it may
be used by others).