debian.dev-zero.nl

In my home directory, I have several subdirectories that contain my software projects, for example:

/home/me
        /src
             /wp-plugin-x
             /project-y
        /config
               /puppet
               /nagios
               /package-z

Some of these trees can get quite deep, and sometimes, when I’m working in one of the directories deep in the tree, I need to access a file somewhere else in the tree. Now, you can do that via ../../../path/to/file, or ~/src/project/path/to/file, but neither are very efficient. I wanted a way to efficiently refer to the root of the current project.

Finding the root is easy. In my case, $(pwd) | cut -d / -f 1-5 gives me what I need. Now I use some Zsh trickery to efficiently use that in commands. I want ‘~~‘ to expand to this directory. Enter the following code in my .zshrc:

my-expand-tilde() {
  local MATCH
  if [[ $LBUFFER = *~ ]]; then
    p=$(pwd | cut -d / -f 1-5)
    LBUFFER=${LBUFFER%~}
    LBUFFER+="${p}/"
  else
    LBUFFER+=~
  fi
}

zle -N my-expand-tilde
bindkey "~" my-expand-tilde

Every time you press ‘~’, the widget ‘my-expand-tilde’ is run. If this is the second ‘~’ in a row, it will strip of the previous ‘~’ and add the root of the current project to the command I am typing. So effectively, whenever I type ‘~~’, it is immediately substituted by the directory that I need.

Ideas for this code where borrowed from ZSH-LOVERS(1), look in that page for a widget named ‘rationalise-dot‘.

After installing Debian on a laptop this week, once again, I ran into the “problem” of not being able to shutdown or reboot the computer, when another user is logged in, for example via SSH. If you’re a Linux user, maybe you have seen it:

System policy prevents restarting the system when other users are logged in

The cause of this behaviour is something called policykit, and a policy defined in /usr/share/polkit-1/actions/org.freedesktop.consolekit.policy. I found several pages on the web, that suggested to modify this file to change the policy. However, as this file is shipped by a package, and living below /usr/share, it is not intended to be modified by users to override the policies it contains.

The correct way to fix the problem is in something called PolicyKit Local Authority, or pklocalauthority. To enable all users to shutdown or reboot the computer, even when other users are logged in, create a file named /etc/polkit-1/localauthority/50-local.d/usershutdown.pkla (the name must end in .pkla) and put the following in it:

[Allow Shutdown]
Identity=unix-user:*
Action=org.freedesktop.consolekit.system.stop-multiple-users
ResultAny=yes
ResultInactive=yes
ResultActive=yes

[Allow Restart]
Identity=unix-user:*
Action=org.freedesktop.consolekit.system.restart-multiple-users
ResultAny=yes
ResultInactive=yes
ResultActive=yes


You may have to reboot the computer (or at least log out and back in) for the policy override to take effect.

This is just a short post, to point out the convenience of a tool named ‘incron‘. Incron is described as an ‘inotify cron‘ system. It behaves much like traditional cron, but instead of time periods, filesystem events are used to trigger certain actions.

In my daily work, quite often I come across situations, where I have to post-process files, that are uploaded to a certain place. For example, a third party regularly uploads video files to one of our servers, and when they do, I have to make sure they are transcoded to a different audio and video format. Enter ‘incron’. It allows you, in a crontab kind of way to define commands, that have to be executed when certain files or directories change.

I have an incron-tab entry, that looks like this:

/home/vod/videofiles IN_MOVED_TO /usr/local/bin/process_upload $#

/home/vod/videofiles is a directory, and when a file is moved into that directory (which is done by the uploading party, through the FTP server) and subsequently the inotify event ‘IN_MOVED_TO‘ is triggered, the process_upload script is fired, with the name of the file (specified as ‘$#‘) as its first argument. Couldn’t be simpler.

Take a look at incron’s web page for more use cases, examples and documentation.

Today, I was looking for a way -on my Ubuntu Lucid workstation- to record audio, but not from a specific source, but let’s say the audio from ‘the system’. In particular, I wanted to record the audio output of a Windows application running under Wine.

After some googling, I found this blog posting, that explains how to record audio from the ‘monitor’ source of a Pulseaudio device. Just what I needed! So I wrote the script below. It uses Gstreamer for the recording, but some ideas for other tools are included as well.

#!/bin/zsh
# A script to record audio from a pulseaudio monitor device
# Needed packages:
# - pulseaudio-utils (for pactl and -if wanted- parec)
# - gstreamer0.10-tools (for gst-launch-0.10)
# - gstreamer0.10-plugins-ugly-multiverse (for lame mp3 encoder)
# - gstreamer0.10-plugins-good (for wavenc)
# - lame (for lame, if wanted)
#
# Ideas from
# http://www.outflux.net/blog/archives/2009/04/19/recording-from-pulseaudio/

FORMAT=mp3
OUT=$1
d=

while getopts wa i
do
 case "$i"
 in
  w)
   FORMAT=wav
   ;;
  a)
   d=`date +%Y%m%d%H%M%S`
   ;;
 esac
done

shift "$(($OPTIND - 1))"

if [ "$d" != "" ]
then
 OUT="/tmp/$d.$FORMAT"
fi

if [ "$OUT" = "" ]
then
 echo "Usage: `basename $0` [-w] <filename>" >&2
 echo "       `basename $0` -a" >&2
 echo "Options:" >&2
 echo " -w               use wav encoding instead of mp3" >&2
 echo " -a               auto-filename, /tmp/<timestamp>.(mp3|wav)" >&2
 exit 1
fi

monitor=$(pactl list | grep -m 1 'Monitor Source' | awk '{print $3}')
if [ "$monitor" = "" ]
then
 echo "Error: no monitor device found" >&2
 exit 1
fi

echo "Using monitor: $monitor"
echo "Recording to : $OUT"
echo "File format  : $FORMAT"

encoder="lame vbr=4 vbr-quality=2"
if [ "$FORMAT" = "wav" ]
then
 encoder="wavenc"
fi

# Some ideas for use of other tools instead of Gstreamer:
#   parec -d "$monitor" | sox -t raw -r 44100 -sLb 16 -c 2 - $OUT.wav
#   parec -d "$monitor" | sox -t raw -r 44100 -sLb 16 -c 2 - $OUT.wav silence 1 0.50 0.1% 1 2.0 0.1% : newfile : restart
#   parec -d "$monitor" | lame -rh - $OUT

gst-launch-0.10 pulsesrc device=$monitor ! queue !
  audio/x-raw-int,rate=44100,channels=2 ! audioconvert !
  $encoder ! filesink location=$OUT

I hope it will be of use to anyone.