Config sources
Each Ceph daemon, process, and library will pull its configuration from several sources, listed below. Sources later in the list will override those earlier in the list when both are present.
the compiled-in default value
the monitor cluster’s centralized configuration database
a configuration file stored on the local host
environment variables
command line arguments
runtime overrides set by an administrator
One of the first things a Ceph process does on startup is parse the configuration options provided via the command line, environment, and local configuration file. The process will then contact the monitor cluster to retrieve configuration stored centrally for the entire cluster. Once a complete view of the configuration is available, the daemon or process startup will proceed.