Debian server DNS bogosity

Note: I’m running my Raspberry Pi as a server, and NetworkManager is not installed.

I discovered that if you want to manually assign search and nameserver entries in your /etc/resolv.conf file, you can’t just add the relevant entries to static entry in /etc/network/interfaces:

For some unknown reason, the resolvconf utility will still attempt to query an upstream DHCP server to get additional name service data. I don’t know why it works this way, I believe it should be hands-off if you’ve specified static in your interfaces file. I finally found that dhcpcd was called to get the info, and added the following line to /etc/dhcpcd.conf to disable actions relating to eth0:

I suppose if I wanted additional interfaces to work properly using dhcp, I’d have to get rid of all this and configure each interface manually via NetworkManager or wicd.

Unison dependency hell

UnisonI would really like to rid myself of Dropbox, but all the alternatives I’ve tried are too bloated, beta- or alpha-quality stage, too complicated to set up, or just plain don’t do what Dropbox does (minus the sharing stuff, which I don’t care about). I don’t want btsync, it’s closed-source. Seafile is too complicated, and makes dubious security claims. Owncloud is a cool project, but their file sync is slow, error prone, and has other limitations. There are some good services, but they don’t run on all the platforms I need, including Mac OSX, Linux x86 (32 and 64-bit), Linux ARMv6 (my Raspberry Pi B) and Android. I ran Syncthing for a while, but the continuous memory usage is pretty steep for the Pi, and I’ve experienced random silent file truncation in my shared directories with it. So I needed something else. Continue reading “Unison dependency hell”

Raspberry Pi can do fast video encoding

Yes, the Raspberry Pi can do fast video encoding. Of course you normally wouldn’t want to re-encode any video with an ARM processor, but that’s not what we’re going to do here. We’re going to leverage the GPU. I should point out before proceeding that the input formats for re-encoding are limited in this method, more about that below.

In order to do this, I’m using a proof-of-concept tool called omxtx, which I think is supposed to be a shortened form of “OpenMAX Transcoding”. Off the top of my head, here are the prerequisites for building the binary from source:

  • Raspbian. It will probably work on other RPi distros, but I haven’t tried them.
  • The build-essential package installed, which you normally need to build anything.
  • Memory split of 64MB for video. I previously had this all the way down to 16 since I don’t use a display on my Pi, but bumping it to only 32MB caused runtime errors from the omxtx binary. You need to give the GPU some breathing room to encode video.
  • There’s probably some libraries you may or may not have installed that the build wants to link in. When I run ldd on my finished binary, it loads all kinds of media libs like libav, libvorbis, libvpx, etc. YMMV.

Continue reading “Raspberry Pi can do fast video encoding”

Raspberry Pi SSH cipher speed

I was curious to see how quickly I could transfer files to my Pi using SSH rather than FTP. Obviously using FTP is way faster than almost any other method, but still I wanted to see how fast I could transfer data over SSH.

Here’s the time it took to transfer a 50 MB file to my Pi using different SSH ciphers.

I later re-tested the aes128-ctr cipher and it took about a second less than what I’d recorded initially. This boils down to:

  • Don’t use triple-DES ever, for both performance and security reasons
  • Most other ciphers give about the same performance, and are generally considered secure
  • arcfour is the fastest class of ciphers, but there is less trust in it from the crypto community. If you’re going to use it, try to avoid the base arcfour cipher and instead use the 128 or 256 version, which tosses out some of the initial bits as a precaution

Enable X11 Forwarding on Raspberry Pi

The usual suspects failed me last night when the $DISPLAY environment variable wasn’t being set after I logged in via SSH to my Pi. The usual suspects being to make sure that the X11 forwarding options were turned on in /etc/ssh/sshd_config on the server and in ssh_config on the client, or to use the command line options -X or -Y.

So I tried logging in again with the debug level turned up (-vvv) and saw the message, X11 forwarding request failed on channel 0. I had remembered from when this happened to me before that you also need a particular package on the server side to allow X11 authentication, whatever package contains the xauth binary. However, it was there and seemed to be working properly.

The Googles turned up this link, which showed that a new option may need to be in your sshd_config on a newer version of OpenSSH:

I then did a sudo service ssh restart, which thankfully is smart enough not to kill your existing SSH session, and logged in again. Finally, I saw

and once again, all was well with the world.