Intro

At work I’ve been doing a lot of Docker based projects. I ended up writing a neat little Bash utility which I then recently extended into what I’m calling DockStat. It shows running containers and their related resources. You could use it if you’re repeatedly upping, downing and destroying docker containers over and over like I was. Or maybe you just want a nice little dashboard to see what’s running on your server?

However, if you have more than say a dozen active containers, this script might not scale nicely (oh, perhaps a monitor in portrait mode might fix this? ;)

Being the good little open source nerd that I am, this is of course available for download with a permissive license in the hopes that some one will find it useful or possibly even offer a PR with some improvements to my nascent Bash coding skills.

Background

With countless primers on how to use Docker out there, I won’t get into what the commands all mean, but the impetus for this script was repeatedly running docker ps to show a list of the active containers. A bit later I remembered you could run endless Bash loops with a one-liner which made the process a bit nicer as it auto-refreshed:

while true; do clear;date;docker ps;sleep 5; done

A bit after that I stumbled upon the glorious watch command! Wow – just when you think that that you know and OS, they come and show you that there’s this awesome command they’ve been hiding from you all these years. Thanks Linux!

watch greatly improved on my Bash one-liner as it was an even short one-liner, could trivially be configured to refresh at what ever frequency you wanted and show a header or not. The icing on the cake was that prevents the flash of a redraw upon refresh:

watch -t -n 1 docker ps

About now I got more cozy with the --format feature built into most Docker command line calls. This was handy because I could reduce the number of fields shown in docker ps that I wasn’t interested in. Here’s maybe the simplest of them which shows JUST the container name and if how long the it has been running:

docker ps --format='{{.Names}} {{.Status}}'

Research continued on how to architect the helper script. I had need to show different data than docker ps had to offer. I branched out into docker inspect as well as finding other Dockeristas one-liners that I shamelessly co-opted (I’d be honored if anyone did the same of my work!!). This allowed me to joined ps and inspect like as seen with this fave that shows all the running containers’ and their internal IPs:

docker ps --format='{{.Names}}'|xargs docker inspect --format='{{.Name}} - {{range .NetworkSettings.Networks}}{{.IPAddress}}{{end}}'

I was ready to assemble all the docker Data dukets I’d gathered into a nice CLI dashboard so our app developers could see the status of our containers booting. Finding a solution for this enabled both the the helper script to spring forth and simultaneously created the nascent DockStat. This was a Bash utility that was both easy to use, automates flash-less refreshes and introduced basic terminal layout functionality with a near zero learning curve (assuming you know Bash): Bash Simple Curses

Thanks

Thanks to James and Russ for reviewing my code and an early draft of this post. I’ve been trying to improve both my posts and code and this won’t happen without folks kind donation of their time and input!

The Problem

Back when I was writing Cattrotar on a Raspberry Pi (or really, any other of the myriad times I was hacking on a small embedded device), I often faced some sort of problem or another:

• I thought I set up the network for a device, but can no longer remotely access it over WiFi
• I’ve just written a new OS to a microSD card, want to further configure the OS but it’s not yet reachable on the network
• I want to take my set up to the hacker space to be social while I work on an issue
• I’m waiting in the library for my kids to finish up a class and can’t easily get my Pi on the library WiFi to hack on it from my laptop
• I don’t want to carry around, or even bother setting up, a keyboard and monitor to get access to my Pi

The Solution

As many of you lovely readers may know, I’m already a fan of small travel routers made by GL.iNet, like the fine GL-MT300N-V2. For a scant $20 dollars (shipped!) you get DHCP server you can not only bring with you, but will happily run off a battery. Better yet, because it has a USB port, you can actually power your Pi off the wee router. Daisy chain USB power for the win! The final icing on the cake is that you can make the two Ethernet ports on be both LAN (instead of LAN & WAN). While these are great devices, their WiFi stack is a bit flaky, so being able to hardwire your network devices is a great, if not slightly cumbersome, work around.

The net result is that your around town bag can have:

• A USB Battery
• Two very short Ethernet cables
• A USB Ethernet dongle (w/ USBC adapter tah boot)
• A travel router (GL-MT300N-V2 in this case)
• Two micro USB cables
• Pi (In the picture below I have an Orange Pi Zero with a temp sensor and a screen threaded through one side of a case)

When you put it all together, you get a nice tidy mess and it works just great, solving all of the above problems. Your laptop can be on two networks so it can have local access to the Pi and to the internet too. Further, if the WiFi your on isn’t too hostile with their captive portals and such, you can actually have the GL.iNet router act as a WiFi repeater and backhaul that bandwidth to your Pi. Run your apt update away!

This set up is not only small and lightweight, but lets me work un-tethered on my Pi setup and Python code. Now if this frickin pandemic would just be solved, I’d actually be able to take this out of the house instead of just co-working with my partner in our office in our house!

Happy Pi Hacking!

13 years ago we got an iPod to actually listen to music on the go. It was awesome! Some time later we had our first kid and some time after that smart phones became prevalent, so our iPod fell out of use. But it was about 9 years ago that we started to use the old iPod as an easy way to play the same a bedtime playlist for our kids (oh yeah, we had a 2nd kid at some point too ;). Soon, the kids split into their own bedrooms so we picked up a used iPod on eBay and loaded up the same bedtime playlist onto it. These two iPods dutifully played the same songs day in and day out every night for years. They’re even more utilitarian than designed, but worked well at their finite task (Photo by Nicnicoleleeolee):

However, over time things started to not work. First one of the fancy docks we used as a speaker stopped charging which ever iPod was in it. This meant every week or so we’d have to swap it over to the good dock to charge up. But then one started to lock up and had to be rebooted. We feared we’d have to replace them soon.

It was around this time that I starting using the Cast All The Things software (aka catt) in my quest to both (finally) learn Python and to easily control the volume on a chromecast. Checkout my cattmate and cattrotar projects! catt is a command line script and python library that allows you to easily control and play videos/music on Chromecasts. It was also around the time that Chomecast Audio’s were stopped being made so I’d stocked up them. We have about 4 or 5 plugged in here and there about the house, including one in each kids room. They work really well!

By now you can likely see how this post is going to resolve itself, but lets find out, shall we?

Yes, that’s right, I wrote a full featured web site that you could pull up and easily play music in which ever room needed to hear the play list. It was simple, yet fancy ;) On the front end there was a series of 2 buttons, one for each room. When you pressed a button, it sent an AJAX call to a to the single endpoint on the back end. The back end then made an exec call to a bash script. This in turn used catt to play a MP3 on the specified Chromecast.

This worked great for a day or so. But then a bug reared it’s ugley had. Let me tell you, the cost of a software bug in your web app which involves waking your child up at 10.30pm is EXTREMELY high. Like, unacceptably high. Sleeping children are gold. Parents get grown up time, the kids get much needed rest and we’re all better for it the next day. Don’t fuck with a kid’s sleep.

After some unfruitful debugging, I got lazy and realized I’d already installed the wonderful termux on my phone, along with a $2 add on to have a bash script launcher widget on my phone’s desktop. So, after a dozen or so minutes of coding and a little ssh-keygen -t ed25519 for good measure, I had this on my phone:

Here’s what happens when you press one of those four links:

1. Call a local script on the phone with the same name shown above
2. Each script has the same contents but just calls the remote server with a different argument: ssh napserver controlmusic.sh CHILD PLAY_STOP. So for the first one above, that’d be ssh napserver controlmusic.sh e play
3. The remote server, (hardened of course to only allowing one command to be run for that SSH key,) inside controlmusic.sh runs a catt command: /usr/bin/catt -d DEVICE COMMAND OPTIONAL_COMMAND. Again for the first button that’d look like: /usr/bin/catt -d "E's Chromecast" cast songs.mp3

So, while not nearly has fancy as the web app I initially wrote, it works every time, has saved me the time of debugging the web app (aka let me be lazy ;) and most importantly, does not wake the kids up after they’ve gone to sleep! Icing on the cake is that continued my lazy streak and bought the app for my partner’s phone so they could activate the playlist while I’m out of town (instead of me VPNing in and activating it remotely on request ;).