Don't trust the kernel version on DigitalOcean

This was tricky. I was setting up a VPN connection with a newly built DigitalOcean droplet (standard debian wheezy 64bit in the London1 data center).

The connection is based on openvpn, and it's the same on many other nodes, but openvpn wasn't starting properly (no sign of the tun interface).

Googling the problem brought me to this reported debian bug, where apparently the problem was associated to an older version of the linux kernel. But I had the latest installed:

ii linux-image-3.2.0-4-amd64 3.2.63-2+deb7u1 amd64 Linux 3.2 for 64-bit PCs

The reason why this problem was present is that the version actually loaded was different!

Apparently

[...] it seems that grub settings are ignored
on digital ocean, and that you instead have to specify which kernel is
booted from the Digital Ocean control panel, loaded from outside the
droplet [...]

So to see what's the actual version loaded you have to go to the console, select Settings, select Kernel and choose the latest (or desired) kernel version, then click on "Change".

Mine was set to:

Debian 7.0 x64 vmlinuz-3.2.0-4-amd64 (3.2.54-2)

Changing and rebooting fixed the issue (see also this about the procedure).

I hope this may save the reader some time.

Troubleshooting TURN

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From time to time I need to verify that the audio inside a trace is as expected. Not much in terms of quality, but more often content and duration. A few years ago I wrote a small program to transform a pcap into a wav file - the codec in use was SILK. These days I'm dealing with Opus , and I have to say things are greatly simplified, in particular if you consider opus-tools , a set of utilities to handle opus files and traces. One of those tools, opusrtp , can do live captures and write the interpreted payload into a .opus file. Still, what I needed was to achieve the same result but from a pcap already existing, i.e. "offline". So I come up with a small - quite shamlessly copy&pasted - patch to opusrtc, which is now in this fork . Once you have a pcap with an RTP stream with opus (say in input.pcap ) you can retrieve the .opus equivalent (in rtpdump.opus ) with: ./opusrtp --extract input.pcap Then you can generate an audible wav file with: ./opusd...

Giacomo Vacca

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