The DiskUsageMonitor monitor can be used to test the amount of free space available on certain storages of a node. The monitor gets information about the available free storage spaces available by inspecting the hrStorageTable of the HOST-RESOURCES-MIB. A storage’s description (as found in the corresponding hrStorageDescr object) must match the criteria specified by the disk and match-type parameters to be monitored. A storage’s available free space is calculated using the corresponding hrStorageSize and hrStorageUsed objects.

The hrStorageUsed doesn’t account for filesystem reserved blocks (i.e., for the super-user), so DiskUsageMonitor will report the service as unavailable only when the amount of free disk space is actually lower than free minus the percentage of reserved filesystem blocks.

This monitor uses SNMP to accomplish its work. Therefore systems against which it is to be used must have an SNMP agent supporting the HOST-RESOURCES-MIB installed and configured. Most modern SNMP agents, including most distributions of the Net-SNMP agent and the SNMP service that ships with Microsoft Windows, support this MIB. Out-of-box support for HOST-RESOURCES-MIB among commercial Unix operating systems may be somewhat spotty.

Monitor Facts

Class Name


Remote Enabled

false, relies on SNMP configuration.

Configuration and Use

Table 1. Monitor specific parameters for the DiskUsageMonitor
Parameter Description Required Default value


A pattern that a storage’s description (hrStorageDescr) must match to be taken into account.




The minimum amount of free space that storages matching the criteria must have available. This parameter is evaluated as a percent of the storage’s reported maximum capacity.




The way how the pattern specified by the disk parameter must be compared to storages description Must be one of the following symbolic operators:
endswith : The disk parameter’s value is evaluated as a string that storages' description must end with;
exact : The disk parameter’s value is evaluated as a string that storages" description must exactly match;
regex : The disk parameter’s value is evaluated as a regular expression that storages' description must match;
startswith : The disk parameter’s value is evaluated as a string that storages' description must start with.
Note: Comparisons are case-sensitive




Destination port where the SNMP requests shall be sent.


from snmp-config.xml


Deprecated. Same as retry. Parameter retry takes precedence when both are set.


from snmp-config.xml

This monitor implements the Common Configuration Parameters.


<!-- Make sure there's at least 5% of free space available on storages ending with "/home" -->
<service name="DiskUsage-home" interval="300000" user-defined="false" status="on">
  <parameter key="timeout" value="3000" />
  <parameter key="retry" value="2" />
  <parameter key="disk" value="/home" />
  <parameter key="match-type" value="endsWith" />
  <parameter key="free" value="5" />
<monitor service="DiskUsage-home" class-name="org.opennms.netmgt.poller.monitors.DiskUsageMonitor" />

DiskUsageMonitor vs. thresholds

Storages' available free space can also be monitored using thresholds if you are already collecting these data.