This document is for a development version of Ceph.

Common Settings

The Hardware Recommendations section provides some hardware guidelines for configuring a Ceph Storage Cluster. It is possible for a single Ceph Node to run multiple daemons. For example, a single node with multiple drives ususally runs one ceph-osd for each drive. Ideally, each node will be assigned to a particular type of process. For example, some nodes might run ceph-osd daemons, other nodes might run ceph-mds daemons, and still other nodes might run ceph-mon daemons.

Each node has a name. The name of a node can be found in its host setting. Monitors also specify a network address and port (that is, a domain name or IP address) that can be found in the addr setting. A basic configuration file typically specifies only minimal settings for each instance of monitor daemons. For example:

mon_initial_members = ceph1
mon_host =


The host setting’s value is the short name of the node. It is not an FQDN. It is NOT an IP address. To retrieve the name of the node, enter hostname -s on the command line. Unless you are deploying Ceph manually, do not use host settings for anything other than initial monitor setup. DO NOT specify the host setting under individual daemons when using deployment tools like chef or cephadm. Such tools are designed to enter the appropriate values for you in the cluster map.


For more about configuring a network for use with Ceph, see the Network Configuration Reference .

Temporary Directory

Some operations will cause a daemon to write to a temporary file. These files are located according to the tmp_dir config.


path for the ‘tmp’ directory





see also


The $TMPDIR environment variable is used to initialize the config, if present, but may be overriden on the command-line. A default may also be set for the cluster using the usual ceph config API.

The template for the temporary files created by daemons is controlled by the tmp_file_template config.


The template file name prefix for temporary files. For example, temporary files may be created by ceph tell commands using the --daemon-output-file switch.



One example where temporary files are created by daemons is the use of the --daemon-output-file=:tmp: argument to the ceph tell command.


Ceph production clusters typically provision at least three Ceph Monitor daemons to ensure availability in the event of a monitor instance crash. A minimum of three Ceph Monitor daemons ensures that the Paxos algorithm is able to determine which version of the Ceph Cluster Map is the most recent. It makes this determination by consulting a majority of Ceph Monitors in the quorum.


You may deploy Ceph with a single monitor, but if the instance fails, the lack of other monitors might interrupt data-service availability.

Ceph Monitors normally listen on port 3300 for the new v2 protocol, and on port 6789 for the old v1 protocol.

By default, Ceph expects to store monitor data on the following path:


You or a deployment tool (for example, cephadm) must create the corresponding directory. With metavariables fully expressed and a cluster named “ceph”, the path specified in the above example evaluates to:


For additional details, see the Monitor Config Reference.


New in version Bobtail: 0.56

Authentication is explicitly enabled or disabled in the [global] section of the Ceph configuration file, as shown here:

auth_cluster_required = cephx
auth_service_required = cephx
auth_client_required = cephx

In addition, you should enable message signing. For details, see Cephx Config Reference.


By default, Ceph expects to store a Ceph OSD Daemon’s data on the following path:


You or a deployment tool (for example, cephadm) must create the corresponding directory. With metavariables fully expressed and a cluster named “ceph”, the path specified in the above example evaluates to:


You can override this path using the osd_data setting. We recommend that you do not change the default location. To create the default directory on your OSD host, run the following commands:

ssh {osd-host}
sudo mkdir /var/lib/ceph/osd/ceph-{osd-number}

The osd_data path must lead to a device that is not shared with the operating system. To use a device other than the device that contains the operating system and the daemons, prepare it for use with Ceph and mount it on the directory you just created by running commands of the following form:

ssh {new-osd-host}
sudo mkfs -t {fstype} /dev/{disk}
sudo mount -o user_xattr /dev/{disk} /var/lib/ceph/osd/ceph-{osd-number}

We recommend using the xfs file system when running mkfs. (The btrfs and ext4 file systems are not recommended and are no longer tested.)

For additional configuration details, see OSD Config Reference.


During runtime operations, Ceph OSD Daemons check up on other Ceph OSD Daemons and report their findings to the Ceph Monitor. This process does not require you to provide any settings. However, if you have network latency issues, you might want to modify the default settings.

For additional details, see Configuring Monitor/OSD Interaction.

Logs / Debugging

You might sometimes encounter issues with Ceph that require you to use Ceph’s logging and debugging features. For details on log rotation, see Debugging and Logging.

Example ceph.conf

fsid = {cluster-id}
mon_initial_members = {hostname}[, {hostname}]
mon_host = {ip-address}[, {ip-address}]

#All clusters have a front-side public network.
#If you have two network interfaces, you can configure a private / cluster 
#network for RADOS object replication, heartbeats, backfill,
#recovery, etc.
public_network = {network}[, {network}]
#cluster_network = {network}[, {network}] 

#Clusters require authentication by default.
auth_cluster_required = cephx
auth_service_required = cephx
auth_client_required = cephx

#Choose reasonable number of replicas and placement groups.
osd_journal_size = {n}
osd_pool_default_size = {n}  # Write an object n times.
osd_pool_default_min_size = {n} # Allow writing n copies in a degraded state.
osd_pool_default_pg_autoscale_mode = {mode} # on, off, or warn
# Only used if autoscaling is off or warn:
osd_pool_default_pg_num = {n}

#Choose a reasonable crush leaf type.
#0 for a 1-node cluster.
#1 for a multi node cluster in a single rack
#2 for a multi node, multi chassis cluster with multiple hosts in a chassis
#3 for a multi node cluster with hosts across racks, etc.
osd_crush_chooseleaf_type = {n}

Naming Clusters (deprecated)

Each Ceph cluster has an internal name. This internal name is used as part of configuration, and as part of “log file” names as well as part of directory names and as part of mountpoint names. This name defaults to “ceph”. Previous releases of Ceph allowed one to specify a custom name instead, for example “ceph2”. This option was intended to facilitate the running of multiple logical clusters on the same physical hardware, but in practice it was rarely exploited. Custom cluster names should no longer be attempted. Old documentation might lead readers to wrongly think that unique cluster names are required to use rbd-mirror. They are not required.

Custom cluster names are now considered deprecated and the ability to deploy them has already been removed from some tools, although existing custom-name deployments continue to operate. The ability to run and manage clusters with custom names might be progressively removed by future Ceph releases, so it is strongly recommended to deploy all new clusters with the default name “ceph”.

Some Ceph CLI commands accept a --cluster (cluster name) option. This option is present only for the sake of backward compatibility. New tools and deployments cannot be relied upon to accommodate this option.

If you need to allow multiple clusters to exist on the same host, use Cephadm, which uses containers to fully isolate each cluster.

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