Mount CephFS: Prerequisites

You can use CephFS by mounting it to your local filesystem or by using cephfs-shell. Mounting CephFS requires superuser privileges to trim dentries by issuing a remount of itself. CephFS can be mounted using kernel as well as using FUSE. Both have their own advantages. Read the following section to understand more about both of these ways to mount CephFS.

Which CephFS Client?

The FUSE client is the most accessible and the easiest to upgrade to the version of Ceph used by the storage cluster, while the kernel client will always gives better performance.

When encountering bugs or performance issues, it is often instructive to try using the other client, in order to find out whether the bug was client-specific or not (and then to let the developers know).

General Pre-requisite for Mounting CephFS

Before mounting CephFS, ensure that the client host (where CephFS has to be mounted and used) has a copy of the Ceph configuration file (i.e. ceph.conf) and a keyring of the CephX user that has permission to access the MDS. Both of these files must already be present on the host where the Ceph MON resides.

  1. Generate a minimal conf file for the client host and place it at a standard location:

    # on client host
mkdir -p -m 755 /etc/ceph
ssh {user}@{mon-host} "sudo ceph config generate-minimal-conf" | sudo tee /etc/ceph/ceph.conf

    Alternatively, you may copy the conf file. But the above method generates a conf with minimal details which is usually sufficient. For more information, see Client Authentication and Bootstrap options.

  2. Ensure that the conf has appropriate permissions:

    chmod 644 /etc/ceph/ceph.conf

  3. Create a CephX user and get its secret key:

    ssh {user}@{mon-host} "sudo ceph fs authorize cephfs client.foo / rw" | sudo tee /etc/ceph/ceph.client.foo.keyring

    In above command, replace cephfs with the name of your CephFS, foo by the name you want for your CephX user and / by the path within your CephFS for which you want to allow access to the client host and rw stands for both read and write permissions. Alternatively, you may copy the Ceph keyring from the MON host to client host at /etc/ceph but creating a keyring specific to the client host is better. While creating a CephX keyring/client, using same client name across multiple machines is perfectly fine.

    Note

    If you get 2 prompts for password while running above any of 2 above command, run sudo ls (or any other trivial command with sudo) immediately before these commands.

  4. Ensure that the keyring has appropriate permissions:

    chmod 600 /etc/ceph/ceph.client.foo.keyring

Note

There might be few more prerequisites for kernel and FUSE mounts individually, please check respective mount documents.