System Variables 

System Variable (sys_var) plugins give you the ability to add new variables that test configs can use in your environment. The variable values are generated by a Python function that you define, which makes the possibilities fairly limitless.

These are used primarily to gather information unique to your systems and environment. Tests can then use that information to tailor themselves to a particular system or deal with other complexities that are unique to your OS or software deployments.

Contents

System Variables
- Files
  - System Variable Module
    - The _get() Method
    - The __init__() Method
      - The ‘is_deferrable’ argument

Files 

System Variable plugins, like all other Pavilion plugins, require a python module and a yapsy-plugin file. See the Plugin Basics for more info on these files and where they should go.

System Variable Module 

A sys_var module should contain a class definition that inherits from the system variable base class.

import pavilion.sys_vars.base_classes as system_plugins

class Uptime(system_plugins.SystemPlugin):
    """This is a fairly useless variable, but is a good enough example."""

    def __init__(self):

        super().__init__(
            # The name of the plugin.
            plugin_name="uptime",
            # The description will be listed when using 'pav show sys_vars'
            description="How long the (kickoff) host has been up in seconds.",
        )

    # This is the method you override to provide the variables value.
    # The base .get() method handles all the deferred variable logic, so
    # you don't have to.
    def _get(self):

        with open('/proc/uptime') as uptime:
            data = uptime.read()

        return data.split()[0]

With this plugin in the system, we can refer to it in test configs:

uptime_test:
  run:
    cmds: echo {{sys.uptime}}

The `_get()` Method 

This should gather the information needed to compute your variables value and then return that value. While the computation of the value can be simple or complex, the returned value must be one of the following:

A string
A dict with a strict set of string keys and string values
A list of such strings or dicts.

Important: If your variable can return dicts, it must always return them. It can’t return dicts sometimes and strings other times. Additionally, dicts returned must always have the same keys, regardless of system or other considerations.

The `init()` Method 

The basics of the __init__() method and it’s generic arguments are covered elsewhere. This plugin type, like most others, can also accept a priority argument that can allow it to override other system variable plugins with the same name.

The ‘is_deferrable’ argument 

If this is set to True, then the variable value lookup will be deferred until right before the test is run within an allocation. This allows you to gather information on a node rather than the kickoff host. Note that any such information gathered will be on the root node of the allocation, not every individual node.

System Variables

Files

System Variable Module

The _get() Method

The __init__() Method

The ‘is_deferrable’ argument