The following documentation discusses the flow, handling and storage of data used by the various Munin components. This includes partially internal processing details, in order to provide a good understanding of data structures within Munin for interested developers.
The Munin Node parses its configuration once during startup.
The Node configuration specifies the details of the node service, which is responding to requests from the Munin Master.
The Node configuration is read from plain text files (e.g. /etc/munin/munin-node.conf).
Its content is stored in a simple perl object (usually called $config).
All settings are available as object attributes (e.g. $config->{default_plugin_user}).
Configuration settings with different names (for compatibility over multiple Munin releases) are
normalized while parsing (see Munin::Node::Config::_parse_line). One example for normalization
is hostname and host_name - both are normalized to fqdn.
During the startup of the Munin Node server, the list of plugins (e.g. below
/etc/munin/plugins) is collected once. Additionally the plugin configuration files
(e.g. below /etc/munin/plugin-conf.d) are parsed. Afterwards all configuration settings
(including wildcard configurations) for all locally enabled plugins are stored in the hash
$config->{sconf}.
Configuration settings for a specific plugin are accessible as a hash ($config->{sconf}{$plugin_name}).
Periodic operations of the Munin Master are executed by munin-cron (via munin-update and munin-limits).
Web resources (html and graphs) are generated by munin-html and munin-graph. Delivery happens either directly (via CGI) or indirectly via munin-httpd.
The Master configuration specifies the details of the update operation (collecting data from nodes), outbound connection details, resource locations, logging and process management.
The Master configuration is read from plain text files (e.g. /etc/munin/munin.conf) by munin-update via Munin::Master::Update->run().
Its content is stored in the :ref:`database storage <data-structure-database>` in table param (see _db_params_update).
All other processes query the database, whenever they need a configuration setting.
The config of every plugin is requested periodically via :ref:`Munin's network protocol <network-protocol>`. The resulting information describe the service, as well as its datasets.
The database is used for exchanging information between different parts of munin.
By default the database is an sqlite3 file stored as /var/lib/munin/datafile.sqlite.
The param table is used for storing Munin Master config parameters. It is populated during every initialization of munin-update (Munin::Master::Update::_db_params_update).
| Field | Value |
|---|---|
| name | name of the configuration setting (e.g. logdir) |
| value | configured value of the configuration setting |
Every configuration setting is stored in the database. The default value is stored in case of a missing explicit setting.
The grp table contains all group/member relationships. Nodes and groups can be members of groups. Thus hierarchical relationships with multiple levels are supported.
| Field | Value |
|---|---|
| id | unique ID |
| p_id | ID of parent group (special group 0: this group has no parent) |
| name | name of the group |
| path | not used anymore |
The node table stores the identity of a Munin Node.
| Field | Value |
|---|---|
| id | unique ID |
| grp_id | ID of the group (or 0 if the node is not part of a group) |
| name | name of the node |
| path | not used anymore |
The node_attr table contains all attributes related to a Munin None.
| Field | Value |
|---|---|
| id | ID of the related node |
| name | name of the attribute (e.g. use_node_name) |
| value | string representation of the value (e.g. 1) |
The service table stores the identity of the service datastructure.
| Field | Value |
|---|---|
| id | unique ID |
| node_id | ID of the node this service belongs to |
| name | unique name of the service within the node |
| service_title | human readable name of the service |
| graph_info | human readable description of the service (see :ref:`graph_info <graph_info>`) |
| subgraphs | number of related graphs produced by this service |
| path | not used anymore |
The service_attr table contains all attributes related to a service.
| Field | Value |
|---|---|
| id | ID of the related service |
| name | name of the attribute (e.g. graph_vlabel) |
| value | string representation of the value (e.g. Bytes) |
Multiple category names can be assigned to a service.
| Field | Value |
|---|---|
| id | ID of the related service |
| category | category name assigned to the service |
Every dataset is described by Field-level attributes (see :ref:`nomenclature`). The collected values for a dataset are stored in an RRD file.
| Field | Value |
|---|---|
| id | unique ID |
| service_id | ID of the service to which this dataset belongs |
| name | unique name of the dataset within the service |
| type | :ref:`field type <fieldname.type>` (e.g. DERIVE) |
| ordr | datasets of a service are sorted according to their respective ordr attribute |
| unknown | TODO |
| warning | description of the warning range (TODO: format?) |
| critical | description of the critical range (TODO: format?) |
| path | not used anymore |
The ds_attr table contains all attributes related to a dataset.
| Field | Value |
|---|---|
| id | ID of the related ds |
| name | name of the attribute (e.g. draw) |
| value | string representation of the value (e.g. AREASTACK) |
The url table is used for caching the URL path of entities (groups, nodes or services). The path is calculated, when the entity is created.
| Field | Value |
|---|---|
| id | ID of the related entity |
| type | text specifying the type of the related entity (one of: group, node and service) |
| path | URL path to be used when accessing the service graphs (e.g. group1/group2/host/plugin/graphFoo/subGraphBar) |
The state table is used for storing the current state of datasets. These values can be used for determining :ref:`alert <tutorial-alert>` conditions.
| Field | Value |
|---|---|
| id | ID of the related entity |
| type | type of the related entity (currently only used as ds) |
| previously_epoch | timestamp of the second to last retrieved value |
| previously_value | second to last retrieved value |
| last_epoch | timestamp of the most recently retrieved value |
| last_value | most recently retrieved value |
| alarm | current state of the related entity (one of: unknown, critical, warning, "" (empty)) |
| num_unknowns | count of recent successively received unknown values (used for delayed "unknown" detection via :ref:`<unknown_limit <fieldname.unknown_limit>`) |