Beaglebone Black – Diary of an Emacs tragic

Howto quickly find your Beaglebone Black’s IP address

Jason — Wed, 23 Jul 2014 02:46:01 +0000

Whenever I connect my Beaglebone Black (BBB) to a network, I have to work out it’s IP address so I can ssh into it. This can be tricky. Some of your options are:

connect to the serial terminal, or connect over the usb network interface which gives the BBB the address 192.168.7.2, log in and issue the command ip addr.
use nmap to try and search out its IP address on your subnet but this is time consuming and not very accurate I have found.
use avahi-browse -rat (thanks Madox for that tip.)

Last night I came up with a Better Way. Rather than trying to determine the BBB’s address, why not use a fully qualified domain name and a dynamic dns service? I could then just type ssh myfqdn.com or whatever and log in. Think how that would simplify one’s life!
To implement this, set up a dynamic DNS somewhere with a FQDN for your BBB. If you happen to have your own domain name already you can use a sub-domain from that. I think its fairly common for DNS hosts to offer an API to update your IP address. I happen to use Rimu Hosting and they have their own simple web api.
Then you just need to write a little script to update the IP address every time the DHCP client receives a new IP address, and drop it into /etc/dhcp/dhclient-exit-hooks.d/
Here is my script. This will only work with Rimu Hosting as they have their own privately developed API, and you’d need to insert your own KEY into the script.

#!/bin/bash
# update ip address with rimu hosting. See https://rimuhosting.com/dns/dyndns.jsp
if [[ ! -z ${new_ip_address} ]]
then
   echo $(date +"%F %T") ${new_ip_address} >> /root/ddns.txt
   curl "https://rimuhosting.com/dns/dyndns.jsp?action=SET&name=clock.emacstragic.net&value=${new_ip_address}&type=A&api_key=XXX"
else
    echo "got no ip"
fi

Update:

I discovered this didn’t work at home. Turns out that dnsmasq in OpenWRT is set to ignore this kind of dns request, due to potential security risks. There is a solution to that. Add a list rebind_domain line to your /etc/config/dhcp line on the router.

config dnsmasq
	.
	.
	.
	list    rebind_domain 'clock.emacstragic.net'

Thanks to Michal Čihař for the solution to that.

Backup your Beaglebone Black

Jason — Fri, 23 May 2014 04:12:12 +0000

Using a method I previously wrote about, it’s quite easy to backup your Beaglebone Black over the network.

ssh root@bbb 'tar cf - / 2>/dev/null' | pv -cN tar \
   | bzip2 | pv -cN bzip2 > bbb-backup-tar.bz2

It runs the bzip compression locally because presumably it will be faster than on the Beaglebone Black. I didn’t actually test that hypothesis though.
pv gives nice little indicators:

    bzip2: 1.81MB 0:00:12 [ 995kB/s] [      <=>                               ]
      tar: 36.2MB 0:00:12 [3.84MB/s] [                             <=>        ]

LED Clock Project

Jason — Mon, 14 Apr 2014 14:39:07 +0000

For a long time I have wanted a bedside clock that would keep accurate time via some external mechanism, and would take care of daylight savings automatically. I eventually decided that the best approach would be to use a wifi enabled device and use the NTP protocol for keeping the time accurate.
After wasting several months hacking away on an Olimex IMX 233 that never worked reliably, I decided to change platform to the Beaglebone Black (BBB).
Along the way I realised there were a few other features I needed:

LEDs should dim with the ambient light so the clock doesn’t light up the whole bedroom
The display needs to be big enough for me to read from across the bedroom without my glasses on.
To make them dimmable I decided to get a pair of
I also needed a power supply that could give 12v for the LED drivers but 5v for the BBB. I found a nice little board on ebay for a few bucks that seems to do the trick. Its called the Benq 12v-5v-3.3v
I hooked that up tonight so now I only need the one power supply to run the LEDs and the BBB.