External check is a check executed by Zabbix server by running a shell script or a binary. However, when hosts are monitored by a Zabbix proxy, the external checks are executed by the proxy.
External checks do not require any agent running on a host being monitored.
The syntax of the item key is:
|script||Name of a shell script or a binary.|
|parameter(s)||Optional command line parameters.|
If you don't want to pass any parameters to the script you may use:
script or script
Zabbix server will look in the directory defined as the location for external scripts (parameter 'ExternalScripts' in Zabbix server configuration file) and execute the command. The command will be executed as the user Zabbix server runs as, so any access permissions or environment variables should be handled in a wrapper script, if necessary, and permissions on the command should allow that user to execute it. Only commands in the specified directory are available for execution.
Do not overuse external checks! As each script requires starting a fork process by Zabbix server, running many scripts can decrease Zabbix performance a lot.
Executing the script check_oracle.sh with the first parameters '-h'. The second parameter will be replaced by IP address or DNS name, depending on the selection in the host properties.
Assuming host is configured to use IP address, Zabbix will execute:
check_oracle.sh '-h' '192.168.1.4'
The return value of the check is standard output together with standard error (the full output with trimmed trailing whitespace is returned since Zabbix 2.0).
A text (character, log or text type of information) item will not become unsupported in case of standard error output.
In case the requested script is not found or Zabbix server has no permissions to execute it, the item will become unsupported and corresponding error message will be set. In case of a timeout, the item will be marked as unsupported as well, an according error message will be displayed and the forked process for the script will be killed.