Wednesday, March 9, 2016

My Weather Station is Back Online

Yep, I got it working. About a week ago my weather station Raspberry Pi died, and predictably, I couldn't get it back up without major work <link>. It's all better now running on a Raspberry Pi model B. Yes, I know that isn't the latest of the Pi series, but I had it already, OK.

The Raspbian Jessie booted to a graphic user interface directly, not to a command line. This was a bit of a surprise because I usually bring up the Pi's I have headless so I don't have to hunt down enough equipment to bring them up on my TV. But, since I had the stuff handy from trying to get it working before I gave up and just reloaded, it came up and I configured it, then stopped the GUI. Loading the GUI makes the boot sequence much longer and I usually just use putty on a laptop to control these machines, I don't need it.

Contrary to many posts out there, the configuration screens worked just fine. I was able to assign a static IP address and finish the configuration easily. There was a little hunting through the various menus and icons to find things, but that's part and parcel of any first time installation.

But installing my stuff turned out to be somewhat harder than I expected because, as usual, every piece of supporting software had changed and I had to hunt down what I needed. I used the latest (as of the date on this post) version of libusb, it was 1.0.20, which was several versions later than the one that I would get from a normal apt-get on the Pi.

This version worked well and had a few 'gotchas's' in it that I had to stumble through to get it to work. There was enough documentation and forum postings out there that I found to help me through the process.

I also used the latest rtl-sdr. It was pretty easy as well, but also had a couple of things that I had to chase down. Then I loaded the version of rtl_433 that I had set aside so I wouldn't have to keep making my changes in that code. With the poking around I did in libusb and rtl-sdr, this piece was super simple.

I hooked them all together by starting things on the command line and it worked well. I was able to read the weatherhead RF signal and save it off to my database. The interface I have to move the data around for viewing worked just as it had before. The only thing left was to implement start up  and restart using systemd instead of upstart.

For those of you that wonder why I needed all this, let me describe what's going on a bit. The usb implementation on the Pi is kernal based and not easily modified by the user. That means I had to get libusb and install it. libusb is a user space interface to the usb capabilities on Linux. Then, I had to be able to read one of those sdr radios so I could find the RF signal from the AcuRite weatherhead. I posted about this earlier <link>. Now that I had the signal, decoding it requires rtl_433 which is a piece of software that was developed to decode the signals of many of the wireless devices available such as thermostats, temperature sensors, door bells, weatherheads, etc.

So, it's software piece piled on software piece piled on ... Sure, I could have incorporated all the things I needed into one piece of software and just ran it, but that's not what leveraging software is all about. You use the piece that does the job you need and add special tweaks specific to your implementation. That saves time and doesn't cost much if anything.

With it working and the only piece left being restarting the processes, I dived into systemd. First though, a tiny bit of background. Unix (and linux came from unix regardless of what people say) has to have something to get it going. This used to be the init process. Init would load the various pieces of software and handle how they interacted. Over time init was replaced with various other things that had more features or less bugs. As is rampant in unix and its derivatives, everyone hated something about each of them. Raspberry Pi uses an operating system called 'Raspbian' which is Debian modified to work specifically on the Pi. There are a ton of other operating systems and the choice of which one to actually use is totally up to the person that installs it. I chose to use Raspian because it was the one the folk that produced the Pi chose to supply. I figured it would have the most support and documentation of various forms over time.

The Raspian that I installed with my first Pi used Sys-V init. This system five init is really old and complex to use. I hate complex, so I replaced it with the clearly superior init process call 'upstart'. Upstart is cool and easy to use once you install it. However, the Debian folk decided that the init process 'systemd' was better and moved to it. Raspberry folk went with the trend and moved to it as well.

That was the decision point that caused me to have to rebuild the weather station Pi from scratch. Upstart wouldn't allow the Pi to boot up at all with the new Jessie level OS that you will get when you update your Pi. But, I did all that and now I faced the dreaded systemd configuration. I looked at about a hundred web sites that discussed how to use systemd to handle starting and restarting a process, and quite honestly, was about to give up because everything was too complex and peppered with 'try this' to give me enough confidence to dive in.

At this point I want to mention that following Linux questions on a forum is so predictable. Someone has a problem and asks for help with it. The first response is to ask for more information about how the system is set up, what they saw that wasn't mentioned in the question, and usually some test or other that can't be run because the problem won't let them. Then a response asking them what they are doing. Then a response that says they should be doing it another way because that way is so much better. Then several posts about how it should be done regardless of the original intent. Lastly, the thread ends with no resolution because the discussion has wandered off into never, never land.

I saw that over and over. I finally stumbled across a blog posting (love blog postings) that whittled all the crap down to something amazingly simple compared to what I had been clicking through for hours <link>. Neil cut all the crap out and just showed how to handle a simple case. I didn't have to dredge through long discussions of 'units' or 'forking' or relative merits of daemons; I could just take his example and use it. It worked first try for one of the processes and third try for the other.

Then I configured logrotate to handle the log files I use for debugging and I was done. Finally.

I still have to back up the SD card and store the image on my NAS, and I'll probably back up the other Pi's just to be somewhat safer (obviously you can't actually be 'safe'). I'll also update my github repo for the various things I changed along the way, but that won't assure me of no problems the next time, just make it somewhat easier to recover.

What will really make it easier the next time is what I learned this time.

6 comments:

  1. Dave:
    "What will really make it easier the next time is what I learned this time." Want to bet. Something will have changed to negate all of your efforts. It's the third law of maintenance and backups.
    The internet is great for asking questions. It's just like the lady who wants a prince....you have to kiss a lot of frogs to get one.
    Glenn.

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    1. That's what I like, lots of encouragement.

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  2. My Pi3 just came in, so I'm starting from scratch again as well! Thanks again for the info you've posted here, it has been a great help.

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    1. Fine, I'm still waiting. I fully expect a full account of what you run into.

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    2. Ended up being much easier than I was expecting. Definitely things went together much better than with my original Pi.

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