The guardian Daemon

The core guardian program is the guardian daemon. It is the program that loads the system module and executes the state machine described therein. It has three modes of operation:

guardian [<options>] <module>
guardian [<options>] <module> <state> [<request>]
guardian [<options>] [ -i <module>]

system search path

daemon EPICS interface

The daemon creates an EPICS channel access interface through which the daemon can be controlled and daemon status

Usually this mode would only be run through the main site supervision infrastructure (see guardctrl below), but it can be run from the command line as well.


INIT state

goto states and redirects


daemon mode

The main state machine execution daemon is launched when guardian is called with a single system name argument:

guardian [<options>] <module>

In this mode, guardian loads the system module and immediately starts execution the state graph starting with the ‘INIT’ state.

The daemon logs to stdout, and is controlled by the guardian EPICS interface.

single state or path execution

If guardian is called with an additional single state argument, the guardian executes the single state code until it completes, at which point guardian exits:

guardian [<options>] <module> <state>

If two additional state arguments are provided, guardian calculates the path between the two states on the state graph. Guardian attempts to execute the path, and exits when the final, request state completes (or an error or ‘jump’ is encountered):

guardian [<options>] <module> <state> <request>

The daemon EPICS interface is not initialized in this mode.

interactive shell

If no argument is specified, guardian launches a special interactive shell:

guardian [<options>]

If a system module is specified with the “interactive” flag, the full system module will be loaded, and the interactive shell will include the full environment of the module:

guardian [<options>] -i <module>

All functions and state methods defined within the system module will be available directly from the interactive prompt.

The interactive shell is a customized instantiation of ipython shell:

$ guardian
aLIGO Guardian Shell
ezca prefix: L1:

In [1]:

It’s useful for testing commands and doing simple math:

In [1]: ezca['SUS-MC2_M2_LOCK_L_GAIN'] * 6
Out[1]: 18

It’s also useful for viewing built-in documentation:

In [2]: help(ezca)