========================
 Mount CephFS using FUSE
========================

`ceph-fuse`_ can be used as an alternative to the :ref:`CephFS kernel
driver<cephfs-mount-using-kernel-driver>` to mount CephFS file systems.
`ceph-fuse`_ mounts are made in userspace. This means that `ceph-fuse`_ mounts
are less performant than kernel driver mounts, but they are easier to manage
and easier to upgrade.

Prerequisites
=============

Ensure that you have all the prerequisites required by both kernel and FUSE
mounts, as listed on the `Mount CephFS: Prerequisites`_ page.

.. note:: Mounting CephFS using FUSE requires superuser privileges (sudo/root).
   The libfuse interface does not provide a mechanism to trim cache entries in
   the kernel so a remount (``mount(2)``) system call is required to force the
   kernel to drop the cached metadata. ``ceph-fuse`` issues these remount
   system calls periodically in response to cache pressure in the MDS or due to
   metadata cache revocations.

Synopsis
========
This is the general form of the command for mounting CephFS via FUSE: 

.. prompt:: bash #

   ceph-fuse {mount point} {options}

Mounting CephFS
===============
To FUSE-mount the Ceph file system, use the ``ceph-fuse`` command::

    mkdir /mnt/mycephfs
    ceph-fuse --id foo /mnt/mycephfs

Option ``--id`` passes the name of the CephX user whose keyring we intend to
use for mounting CephFS. In the above command, it's ``foo``. You can also use
``-n`` instead, although ``--id`` is evidently easier::

    ceph-fuse -n client.foo /mnt/mycephfs

In case the keyring is not present in standard locations, you may pass it
too::

    ceph-fuse --id foo -k /path/to/keyring /mnt/mycephfs

You may pass the MON's socket too, although this is not mandatory::

    ceph-fuse --id foo -m 192.168.0.1:6789 /mnt/mycephfs

You can also mount a specific directory within CephFS instead of mounting
root of CephFS on your local FS::

    ceph-fuse --id foo -r /path/to/dir /mnt/mycephfs

If you have more than one FS on your Ceph cluster, use the option
``--client_fs`` to mount the non-default FS::

    ceph-fuse --id foo --client_fs mycephfs2 /mnt/mycephfs2

You may also add a ``client_fs`` setting to your ``ceph.conf``. Alternatively, the option
``--client_mds_namespace`` is supported for backward compatibility.

Unmounting CephFS
=================

Use ``umount`` to unmount CephFS like any other FS::

    umount /mnt/mycephfs

.. tip:: Ensure that you are not within the file system directories before
   executing this command.

Persistent Mounts
=================

To mount CephFS as a file system in user space, add the following to ``/etc/fstab``::

       #DEVICE PATH       TYPE      OPTIONS
       none    /mnt/mycephfs  fuse.ceph ceph.id={user-ID}[,ceph.conf={path/to/conf.conf}],_netdev,defaults  0 0

For example::

       none    /mnt/mycephfs  fuse.ceph ceph.id=myuser,_netdev,defaults  0 0
       none    /mnt/mycephfs  fuse.ceph ceph.id=myuser,ceph.conf=/etc/ceph/foo.conf,_netdev,defaults  0 0

Ensure you use the ID (e.g., ``myuser``, not ``client.myuser``). You can pass
any valid ``ceph-fuse`` option to the command line this way.

To mount a subdirectory of the CephFS, add the following to ``/etc/fstab``::

       none    /mnt/mycephfs  fuse.ceph ceph.id=myuser,ceph.client_mountpoint=/path/to/dir,_netdev,defaults  0 0

``ceph-fuse@.service`` and ``ceph-fuse.target`` systemd units are available.
As usual, these unit files declare the default dependencies and recommended
execution context for ``ceph-fuse``. After making the fstab entry shown above,
run following commands::

    systemctl start ceph-fuse@/mnt/mycephfs.service
    systemctl enable ceph-fuse.target
    systemctl enable ceph-fuse@-mnt-mycephfs.service

See :ref:`User Management <user-management>` for details on CephX user management and `ceph-fuse`_
manual for more options it can take. For troubleshooting, see
:ref:`ceph_fuse_debugging`.

.. _ceph-fuse: ../../man/8/ceph-fuse/#options
.. _Mount CephFS\: Prerequisites: ../mount-prerequisites
