vSphere includes a user-configurable events and alarms subsystem. This subsystem tracks events happening throughout vSphere and stores the data in log files and the vCenter Server database. This subsystem also enables you to specify the conditions under which alarms are triggered. Alarms can change state from mild warnings to more serious alerts as system conditions change, and can trigger automated alarm actions. This functionality is useful when you want to be informed, or take immediate action, when certain events or conditions occur for a specific inventory object, or group of objects.


Events are records of user actions or system actions that occur on objects in vCenter Server or on a host. Actions that might be recorded as events include, but are not limited to, the following examples:
  • A license key expires
  • A virtual machine is powered on
  • A user logs in to a virtual machine
  • A host connection is lost

Event data includes details about the event such as who generated it, when it occurred, and what type of event it is. There are three types of events:

  • Information
  • Warning
  • Error

In the vSphere Web Client, event data is displayed in the Monitor tab. See View Events.


Alarms are notifications that are activated in response to an event, a set of conditions, or the state of an inventory object. An alarm definition consists of the following elements:

  • Name and description - Provides an identifying label and description.
  • Alarm type - Defines the type of object that is monitored.
  • Triggers - Defines the event, condition, or state that triggers the alarm and defines the notification severity.
  • Tolerance thresholds (Reporting) - Provides additional restrictions on condition and state triggers thresholds that must be exceeded before the alarm is triggered. Thresholds are not available in the vSphere Web Client.
  • Actions - Defines operations that occur in response to triggered alarms. VMware provides sets of predefined actions that are specific to inventory object types.
Alarms have the following severity levels:
  • Normal – green
  • Warning – yellow
  • Alert – red

Alarm definitions are associated with the object selected in the inventory. An alarm monitors the type of inventory objects specified in its definition.

For example, you might want to monitor the CPU usage of all virtual machines in a specific host cluster. You can select the cluster in the inventory, and add a virtual machine alarm to it. When enabled, that alarm monitors all virtual machines running in the cluster and triggers when any one of them meets the criteria defined in the alarm. To monitor a specific virtual machine in the cluster, but not others, select that virtual machine in the inventory and add an alarm to it. To apply the same alarms to a group of objects, place those objects in a folder and define the alarm on the folder.

Note: You can enable, disable, and modify alarms only from the object in which the alarm is defined. For example, if you defined an alarm in a cluster to monitor virtual machines, you can only enable, disable, or modify that alarm through the cluster. You cannot change the alarm at the individual virtual machine level.

Alarm Actions

Alarm actions are operations that occur in response to the trigger. For example, you can have an email notification sent to one or more administrators when an alarm is triggered.

Note: Default alarms are not preconfigured with actions. You must manually set what action occurs when the triggering event, condition, or state occurs.