Alarms are notifications that occur in response to selected events, conditions, and states that occur with objects in the inventory. You use the vSphere Client to create and modify alarms.

The vCenter Server system is configured with a set of predefined alarms that monitor clusters, hosts, datacenters, datastores, networks, and virtual machines. it is also configured with alarms that monitor vCenter Server licensing.

Each predefined alarm monitors a specific object and applies to all objects of that type. For example, by default, the Host CPU Usage alarm is set automatically on each host in the inventory and triggers automatically when any host's CPU usage reaches the defined CPU value.

If the predefined vCenter Server alarms do not account for the condition, state, or event you need to monitor, you can define custom alarms.

When you set an alarm on a parent object, such as a vCenter Server, a datacenter, or a cluster, all applicable child objects inherit the alarm. You can also set an alarm on a folder to propagate the same alarm to all objects contained in that folder. You cannot change or override an alarm that is set on a child object from its parent object. You must change the alarm on the child object itself.

Alarms are composed of a trigger and an action.


A set of conditions that must be met for an alarm warning and alert to occur. Most triggers consist of a condition value and a length of time that value is true. For example, the virtual machine memory alarm triggers a warning when memory usage is over 75% for one hour and over 90% for five minutes.

VMware uses colors to denote alarm severity:

Normal – green

Warning – yellow

Alert – red

You can set alarms to trigger when the state changes from green to yellow, yellow to red, red to yellow, and yellow to green. Triggers are defined for the default VMware alarms. You can change the trigger conditions (thresholds, warning values, and alert values) for the default alarms.


The operation that occurs in response to the trigger. For example, you can have an email notification sent to one or more administrators when an alarm is triggered. The default vCenter Server alarms are not preconfigured with actions. You must manually set what action occurs when the triggering event, condition, or state occurs.


Some alarms contain triggers that are not supported in the vSphere Client and cannot be changed. However, you can still configure the alarm actions, enable or disable the alarm, and change the alarm name. If your environment requires changes to these alarm triggers, create custom alarms by using the vSphere Client or the VMware vSphere APIs.