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.. _event-handler:
#############
Event Handler
#############
*********************************
Event Handler Technology Overview
*********************************
Event handler allows you to execute scripts when a string that matches a regex or a regex with
a service name appears in journald logs. You can pass variables, arguments, and a full matching string to the script.
******************************
How to configure Event Handler
******************************
`1. Create an event handler`_
`2. Add regex to the script`_
`3. Add a full path to the script`_
`4. Add optional parameters`_
*********************************
Event Handler Configuration Steps
*********************************
1. Create an event handler
==========================
.. cfgcmd:: set service event-handler event <event-handler name>
This is an optional command because the event handler will be automatically created after any of the next commands.
2. Add regex to the script
===========================================
.. cfgcmd:: set service event-handler event <event-handler name> filter pattern <regex>
This is a mandatory command. Sets regular expression to match against log string message.
.. note:: The regular expression matches if and only if the entire string matches the pattern.
3. Add a full path to the script
================================
.. cfgcmd:: set service event-handler event <event-handler name> script path <path to script>
This is a mandatory command. Sets the full path to the script. The script file must be executable.
4. Add optional parameters
==========================
.. cfgcmd:: set service event-handler event <event-handler name> filter syslog-identifier <sylogid name>
This is an optional command. Filters log messages by syslog-identifier.
.. cfgcmd:: set service event-handler event <event-handler name> script environment <env name> value <env value>
This is an optional command. Adds environment and its value to the script. Use separate commands for each environment.
One implicit environment exists.
* ``message``: Full message that has triggered the script.
.. cfgcmd:: set service event-handler event <event-handler name> script arguments <arguments>
This is an optional command. Adds arguments to the script. Arguments must be separated by spaces.
.. note:: We don't recomend to use arguments. Using environments is more preffereble.
*******
Example
*******
Event handler that monitors the state of interface eth0.
.. code-block:: none
set service event-handler event INTERFACE_STATE_DOWN filter pattern '.*eth0.*,RUNNING,.*->.*'
set service event-handler event INTERFACE_STATE_DOWN filter syslog-identifier 'netplugd'
set service event-handler event INTERFACE_STATE_DOWN script environment interface_action value 'down'
set service event-handler event INTERFACE_STATE_DOWN script environment interface_name value 'eth2'
set service event-handler event INTERFACE_STATE_DOWN script path '/config/scripts/eventhandler.py'
Event handler script
.. code-block:: none
#!/usr/bin/env python3
#
# VyOS event-handler script example
from os import environ
import subprocess
from sys import exit
# Perform actions according to requirements
def process_event() -> None:
# Get variables
message_text = environ.get('message')
interface_name = environ.get('interface_name')
interface_action = environ.get('interface_action')
# Print the message that triggered this script
print(f'Logged message: {message_text}')
# Prepare a command to run
command = f'sudo ip link set {interface_name} {interface_action}'.split()
# Execute a command
subprocess.run(command)
if __name__ == '__main__':
try:
# Run script actions and exit
process_event()
exit(0)
except Exception as err:
# Exit properly in case if something in the script goes wrong
print(f'Error running script: {err}')
exit(1)
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