Notice
This document is for a development version of Ceph.
Mount CephFS using Kernel Driver
The CephFS kernel driver is part of the Linux kernel. It makes possible the mounting of CephFS as a regular file system with native kernel performance. It is the client of choice for most use-cases.
Note
The CephFS mount device string now uses a new syntax (“v2”). The mount helper is backward compatible with the old syntax. The kernel is backward-compatible with the old syntax. This means that the old syntax can still be used for mounting with newer mount helpers and with the kernel.
Prerequisites
Complete General Prerequisites
Go through the prerequisites required by both kernel and FUSE mounts, as described on the Mount CephFS: Prerequisites page.
Is mount helper present?
The mount.ceph
helper is installed by Ceph packages. The helper passes the
monitor address(es) and CephX user keyrings, saving the Ceph admin the effort
of passing these details explicitly while mounting CephFS. If the helper is not
present on the client machine, CephFS can still be mounted using the kernel
driver but only by passing these details explicitly to the mount
command.
To check whether mount.ceph
is present on your system, run the following
command:
stat /sbin/mount.ceph
Which Kernel Version?
Because the kernel client is distributed as part of the Linux kernel (and not as part of the packaged Ceph releases), you will need to consider which kernel version to use on your client nodes. Older kernels are known to include buggy Ceph clients and may not support features that more recent Ceph clusters support.
Remember that the “latest” kernel in a stable Linux distribution is likely to be years behind the latest upstream Linux kernel where Ceph development takes place (including bug fixes).
As a rough guide, as of Ceph 10.x (Jewel), you should be using a least a 4.x kernel. If you absolutely have to use an older kernel, you should use the fuse client instead of the kernel client.
This advice does not apply if you are using a Linux distribution that includes CephFS support. In that case, the distributor is responsible for backporting fixes to their stable kernel. Check with your vendor.
Synopsis
This is the general form of the command for mounting CephFS via the kernel driver:
mount -t ceph {device-string}={path-to-mounted} {mount-point} -o {key-value-args} {other-args}
Mounting CephFS
CephX authentication is enabled by default in Ceph clusters. Use the mount
command to use the kernel driver to mount CephFS:
mkdir /mnt/mycephfs
mount -t ceph <name>@<fsid>.<fs_name>=/ /mnt/mycephfs
name
is the username of the CephX user we are using to mount CephFS.fsid
is the FSID of the Ceph cluster, which can be found using theceph fsid
command.fs_name
is the file system to mount. The kernel driver requires a ceph Monitor’s address and the secret key of the CephX user. For example:mount -t ceph cephuser@b3acfc0d-575f-41d3-9c91-0e7ed3dbb3fa.cephfs=/ -o mon_addr=192.168.0.1:6789,secret=AQATSKdNGBnwLhAAnNDKnH65FmVKpXZJVasUeQ==
When using the mount helper, monitor hosts and FSID are optional. The
mount.ceph
helper discovers these details by finding and reading the ceph
conf file. For example:
mount -t ceph cephuser@.cephfs=/ -o secret=AQATSKdNGBnwLhAAnNDKnH65FmVKpXZJVasUeQ==
Note
Note that the dot (.
in the string cephuser@.cephfs
) must be
a part of the device string.
A weakness of this method is that it will leave the secret key in your shell’s
command history. To avoid this, copy the secret key inside a file and pass the
file by using the option secretfile
instead of secret
. For example:
mount -t ceph cephuser@.cephfs=/ /mnt/mycephfs -o secretfile=/etc/ceph/cephuser.secret
Ensure that the permissions on the secret key file are appropriate (preferably,
600
).
Multiple monitor hosts can be passed by separating addresses with a /
:
mount -t ceph cephuser@.cephfs=/ /mnt/mycephfs -o
mon_addr=192.168.0.1:6789/192.168.0.2:6789,secretfile=/etc/ceph/cephuser.secret
If CephX is disabled, omit any credential-related options. For example:
mount -t ceph cephuser@.cephfs=/ /mnt/mycephfs
Note
The Ceph user name must be passed as part of the device string.
To mount a subtree of the CephFS root, append the path to the device string:
mount -t ceph cephuser@.cephfs=/subvolume/dir1/dir2 /mnt/mycephfs -o secretfile=/etc/ceph/cephuser.secret
Backward Compatibility
The old syntax is supported for backward compatibility.
To mount CephFS with the kernel driver, run the following commands:
mkdir /mnt/mycephfs
mount -t ceph :/ /mnt/mycephfs -o name=admin
The key-value argument right after the option -o
is the CephX credential.
name
is the username of the CephX user that is mounting CephFS.
To mount a non-default FS (in this example, cephfs2
), run commands of the following form. These commands are to be used in cases in which the cluster
has multiple file systems:
mount -t ceph :/ /mnt/mycephfs -o name=admin,fs=cephfs2
or
mount -t ceph :/ /mnt/mycephfs -o name=admin,mds_namespace=cephfs2
Note
The option mds_namespace
is deprecated. Use fs=
instead when
using the old syntax for mounting.
Unmounting CephFS
To unmount the Ceph file system, use the umount
command, as in this
example:
umount /mnt/mycephfs
Tip
Ensure that you are not within the file system directories before executing this command.
Persistent Mounts
To mount CephFS in your file systems table as a kernel driver, add the
following to /etc/fstab
:
{name}@.{fs_name}=/ {mount}/{mountpoint} ceph [mon_addr={ipaddress},secret=secretkey|secretfile=/path/to/secretfile],[{mount.options}] {fs_freq} {fs_passno}
For example:
cephuser@.cephfs=/ /mnt/ceph ceph mon_addr=192.168.0.1:6789,noatime,_netdev 0 0
If the secret
or secretfile
options are not specified, the mount
helper will attempt to find a secret for the given name
in one of the
configured keyrings.
See User Management for details on CephX user management and the mount.ceph manual for a list of the options it recognizes. For troubleshooting, see Kernel mount debugging.
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