This field, which appears under the “Common settings” tab of a Host definition, is used to specify the command that should be used to check if the host is up or down. If you leave this argument blank, the host will not be actively checked. Application Performance Monitor will then likely always assume the host is up. This is useful if you are monitoring devices that are frequently turned off, or when you want to save some resources because you are monitoring thousands of devices.
By default, this check is defined and active and uses a ping command to check a host. You may also remark that depending on the command you select under the “Check command” field, the “Command view” will automatically be adjusted to display the corresponding command parameter used by the command.
Note: Usually, for a host definition, only the “check-host-alive” command or a blank command should be used. The other commands do not apply to this context.