There are various ways for you to communicate with a CX2020 from Linux, it all depends on your requirements and what the usage is for.
Without knowing anything about those, one option is to use the Beckhoff ADS protocol. All Beckhoff PLCs have by default ADS installed on them and you can
(with the right credentials setup for ADS) communicate with the ADS-library. The good thing about ADS is that it is open-source, and thus it's possible to
get the code for Linux.
The ADS sourcecode is available at:
https://github.com/Beckhoff/ADS
You basically need to:
- Compile/Install the library on your Linux machine
- Create an ADS/AMS-route to your CX2020
- Create a program that uses this route to communicate with the PLC
With ADS you can access the variables directly in the CX2020 memory (both read and write!).
There are many finished wrapper libraries available for all common programming languages that you can use directly in Linux. If you're up to Python, I would
recommend checking out PyADS (https://github.com/stlehmann/pyads), which has a good user base and many examples available all around the net.