DigitalLife

How to backup a Raspberry Pi SD card on a Mac

One thing that is quite appealing about the Raspberry Pi is that the entire state of the system is on one tiny SD card. Clone the card and you clone the system. Copy the card and you have backed up the system. Re-flash the card with an old image and you have returned the system to a known good state. There are lots of possibilities here.

Being able to write an image to a card is pretty much an essential in the Raspberry Pi world (unless you resort to only buying pre-written NOOBS SD cards). Luckily writing an image to a card is really easy with the elegant, free Etcher.

Creating an image from a card seems slightly more challenging. A bit of Duck Duck Going (or Googling if you are into that sort of thing) will lead to a number of sites explaining how to do this from the command line with dd. I found only one site suggesting using Disk Utility and suggesting a process that would allow me to use Etcher with the resulting file. Sadly following the instructions didn’t work for me.

After a fair bit of fiddling around I managed to get this working for me. It is a simple process, but there are two little wrinkles to be aware of:

1.    Make an image of the entire “drive” not just the partition.
2.    Format the image as “DVD/CD Master” and then rename the .cdr file to .iso for use with Etcher.

So here is how to do it in a little more detail:


1.    Insert the SD card into the card reader.

2.   Open Disk Utility and locate your card reader. Using the internal reader in my Mac and a freshly minted Raspbian card this is what I see:

SD-Copy-1.png

3.    Select the drive (not the boot partition) and select File | New Image | Image from “Untitled”.

4.    In the Save As dialog set the format to “DVD/CD Master”. This will create a .cdr file.

5.    Save the new image. This could take a while (~20 mins on my machine for a 16Gb disk). If this only takes a minute or less you have probably selected the boot partition and not the whole card.

6.    Rename the .cdr to .iso and it is ready for use with Etcher.


To be frank, I am not convinced that this is the optimal way to do this. It is a slow process as you spend a lot of time carefully copying blank space. I will experiment some more, but in the meantime this process works for me.

Happy copying and flashing!

Reawakening the inner geek

I have always been a Lego person. It was one of my favourite toys as a child and still has a place in my life as an adult and a Dad (although sharing might not be my strong suit).

As a bit of a geek I was always taken with the idea of Mindstorms. I got the original Mindstorm kit (with the big yellow RCX brick and the IR transmitter) and played around with it a little, but never really got into it. When EV3 was released I lusted after it but hesitated because of my earlier experience. Eventually my wonderful wife gave me a set as a present. Again I played around for a while, but it never really grabbed me.

Recently I dragged it back out and started to play, and this time I got hooked. The key thing for me was finding ev3dev!

I had always quickly become frustrated with the block-based programming tools that Lego provides. Perhaps they are great for kids (although I have my doubts), but for me they are painfully cumbersome and limited. I wanted a command line, an IDE and the concise power of a full function textual language.

I knew that it was possible to use a custom Linux instal on the EV3 brick and use a range of ‘real’ languages. When I investigated this in the past I was put off by the idea of changing the firmware. This seemed like a great way of potentially bricking my brick, and then needing to invest significant time in getting it back to a working state.

This time when I investigated the options I found ev3dev. The thing that immediately caught my eye was that it ran off a microSD card rather than requiring a firmware change. As soon as I saw this I was off. Within an hour I had downloaded ev3Dev, flashed it to a card, had the brick up and running, and connected to it with SSH.

Just seeing the “robot@ev3dev:~$” prompt on the terminal window of my Mac was a complete game changer. Imaging the possibilities! It is the same feeling I had as a kid when I found that the TRS-80 BASIC could do 3-D arrays, or when playing with 6502 assembler on the Apple ][. This is why I love technology.

I decided to start with Python, a language I do not know well and want to know better. I grabbed a copy of PyCharm Edu, set-up a GIT project on the brick and started coding (see note 1 below). I had been playing with a basic robot based on the Lego Educator Vehicle (modified because I do not have the EV3 Education kit) and had been doing simple line following using the block based system. I quickly had a Python version running, and was able to refine it without all of he frustrations that I had been hitting.

My next project was to build a plotter. As a teenager on work experience at a computer centre in the 80’s I spent many happy hours watching a plotter at work, and have never lost the fascination with them. It took a few hours to build a basic working version, and a few more hours to refine and extend it, and generally tinker. It was all highly satisfying.

Thank you EV3 for reminding me what it feels like to be a geeky kid again!


1. With hindsight, GIT was probably overkill and I would have been better off just using scp to push the single python files from Mac to brick.

A Cliff Stoll moment?

I like to think that I maintain a healthy level of paranoia when it comes to computer and online security. Come to think of it, just writing that sentence probably puts me out of “healthy” and fairly deep into “paranoid” territory.

The challenge is that odd things happen sometimes and it is hard to know whether it is just the normal random weirdness of everyday IT life, or malicious action. A large amount of time and brain cycles can be spent trying to figure this out.

This reminds me of one of the formative books of my youth, Cliff Stoll’s 1989 classic “The Cuckoo’s Egg” (which coincidentally I found has been reprinted recently). Cliff was an astronomer working as a sys admin who started looking into a 75 cent accounting discrepancy and ended up spending a couple of years tracking a group of German hackers (and no, lets not get wrapped up in the terminology here).

So every time I find myself thinking “That’s odd…” and firing up a terminal session, I wonder whether I am having a Cliff Stoll moment, or just being paranoid. So far I haven’t uncovered any worldwide hacker conspiracies, but every time I dive down the rabbit hole I learn something.

My most recent example was when I powered up my iMac and Safari popped up showing the following:

Now I don’t have my machine configured to restart open windows on launch, or start Safari on login so this was a bit of a surprise.

Somewhat worryingly the page title was “Test živého HTTP steamování”. Images of Eastern European hackers or organised crime types came to mind.

Google Translate helpfully identified the language as Lithuanian, but less helpfully translated it into English as “Test živého HTTP steamování”. It actually likes “živého” as “live” in Czech, but still likes “steamování” as Lithuanian for “steamování” in English. Nevertheless it does’t seem too much of stretch to assume it is something like “Test live HTTP streaming”.

Like any sensible person faced with a quandary my first course of action was to google it (OK, actually I Duck Duck Goed it. I’m not going to give the Evil Empire even more information about me. No, sorry that’s Bing isn’t it. I mean the Googleplex. Oops, my foil hat has slipped, just a sec …).

After all if anything unusual is happening in the world x thousand people will have asked about it already on stack exchange or the Apple support forums or Yahoo answers or wherever. And a nice distinctive string like “Test živého HTTP steamování” should cut through the cruft. But no, no sign of this being the calling card of the latest tsunami of Mac ransomware or similar. Unless of course I am the first person on the planet to fall victim …

A little investigation showed that the culprit was a login item opening an HTML page buried deep in the bowels of the iMovie app bundle. The final bits of the path were /cs.lproj/CreateLiveStreamingMovieIndex.html

Aha! “cs.lproj”! Of course, a localisation into Czech, cs being the ISO 639-1 language code for Czech, not to be confused with the ISO 3166-2 country code cs for Serbia and Montenegro, at least until 2006 when it was replaced by separate codes for Serbia and Montenegro … but I digress.

Looking at the en.lproj version of the file showed the title “HTTP Live Streaming Test”.

So I am sitting looking alternately at the words “Live streaming” and the doleful eye of my iMac webcam. Is this the time to break out the tape to cover my webcam? After all, if it’s good enough for FBI Director James Comey surely it’s good enough for me. If anybody noticed I could even use his “I saw somebody smarter than I am do it” defence.

Perhaps not quite yet. Time to look at the HTML. The only material line appears to be:

<video src=“$(MEDIA_HTML_ESCAPED)” controls autoplay></video>

Now I don’t claim any expertise at HTML or Unix scripting, but as far as I can see the video tag is purely for media playback. So it is some sort of test page for streaming video, which just displays the video from …

Here my lack of HTML knowledge becomes a problem. The src attribute is supposed to specify the source URL. At first look I assumed it was simply dereferencing an environment variable like in a Unix shell - $MEDIA_HTML_ESCAPED. But in a shell the brackets would make this a command substitution with the command being MEDIA_HTML_ESCAPED. If this were a variable containing a command it would need to be dereferenced again, as in $($MEDIA_HTML_ESCAPED). But this is HTML not a shell so … I don’t know.

Any amount of Googling (or DDGing) does’t make up for my lack of web development basic syntax knowledge here. And of course there is a world of difference between dereferencing a string variable and executing arbitrary code. After running this by a web savvy friend, I wonder whether this file is actually for use as a template to generate test pages. In the context of resources within an app bundle this could make sense.

Assuming for the moment that this is just a benign Czech video streaming test page (admittedly not a phrase I have frequent cause to use), the obvious question is how it ended up as a login item on my machine.

It is part of an Apple product called qmaster which appears to be an interface for submitting video editing tasks. This in turn seems to be part of iMovie. iMovie is not an application I use, but it is on my machine (in fact three versions are on my machine for some reason) and I did take the update to 10.1.1 just before this all started.

Presumably, somehow this update ended up putting this obscure little page in my login items list for some reason. This seems like an odd bug, but right now seems more likely than some grand conspiracy by Czech speaking video streaming trolls.

I will simply remove the login item and hope that that is that, and that my next post won’t be “How my streaming video went viral in Eastern Europe” or “My adventures with Ransomware”.

Of course if MEDIA_HTML_ESCAPED was https://www.youtube.com/watch?v=dQw4w9WgXcQ it would all have make perfect sense ;)

PS - Apologies to any readers who stuck it out this far hoping for some useful resolution or startling revelation. Sorry. Welcome to my world.