Startup Configuration

There are a number of startup settings that you can configure, including JAVA_HEAP_SIZE. Horizon startup scripts load ${OPENNMS_HOME}/etc/opennms.conf early in their startup, if that file exists.

No opennms.conf exists in the default RPM/DEB installation, but ${OPENNMS_HOME}/etc/examples includes a sample file that you can use as a starting point.

Table 1. Variables you may want to set
Variable	Description	Default	Behavior
`JAVA_HEAP_SIZE`	Specifies the maximum amount of memory the JVM should use. You may want to increase this value if you experience long response times, frequent garbage collection that takes a lot of time, or see alarms that should have been cleared automatically still listed as alarms. See performance tuning on Discourse for more information.	2048	Units are in megabytes. Suffix `m` is added automatically with the result passed to JVM as an `-Xmx` flag.
`JAVA_INITIAL_HEAP_SIZE`	Specifies the initial amount of memory the JVM should use. Effectively sets a minimum memory value when used in conjunction with `JAVA_HEAP_SIZE`. You may want to increase this value if you experience long response times, frequent garbage collection that takes a lot of time, or see alarms that should have been cleared automatically still listed as alarms. It is good practice to set the `JAVA_INITIAL_HEAP_SIZE` and `JAVA_HEAP_SIZE` to the same value.	null	Units are in megabytes. Suffix `m` is added automatically with the result passed to JVM as an `-Xms` flag.
`ADDITIONAL_MANAGER_OPTIONS`	Additional options to pass to Java when starting Horizon.		Appended to other JVM startup flags.
`MAXIMUM_FILE_DESCRIPTORS`	You may want to change these values if you end up with too many "files open exceptions" in Horizon. See How to investigate file descriptor issues on Discourse for more information.	20480	Passed to `ulimit -n` before starting JVM.
`MAXIMUM_SIZE_STACK_SEGMENT`	Defines the size limit for each Java thread in the JVM.	8192	Units are in kilobytes. Passed to `ulimit -s` before starting JVM.