Tag Archives: pulseaudio

Restarting the Linux sound subsystem

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Sometimes my laptop gets to a state in which sound works through the built-in speakers, but not through the headphone jack. Possibly my solution is too brutal, but it works -  restarting the whole sound subsystem. I guess that it may come handy in other situation: the ability to restart a subsystem instead of rebooting the machine, is always an advantage.

The rationale is simply reloading the kernel module that acts as a driver to our sound hardware. Reloading isn't easy, as:

  1. Kernel modules use this module.
  2. User processes use this module.

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Avahi and other (relatively) new desktop technologies

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Every time when I try to sit and study, I find something better to do. This time it was playing with Avahi and some avahi clients such as pidgin, amarok, pulseaudio.

What is Avahi?

A free zeroconf implementation which is very common on Linux distros, just as Bonjour is Apple's zeroconf implementation. AKA multicast DNS (mDNS), and is probably similar to the Microsoft-backed UPnP.
Long story short: it allows discovering and resolving the available services on the LAN (if they're zeroconf-aware, of course)

How do I use Avahi?

  • Discovering: If the avahi daemon is installed and running, the magical command avahi-browse -a (might require the avahi-utils package) would query and display all the available services.
  • Resolving: the following weird hosts line in /etc/nsswitch.conf enables resolving through avahi (usually with the .local suffix, i.e. ping mymachine.local):

    hosts:          files dns mdns4_minimal [NOTFOUND=return]

Software using Avahi out of the box:

  • Pidgin: simply add a new Bonjour account, and you'll be able to instantly talk to your LAN-neighbors.
  • CUPS or other printer config frontends: find zeroconf-supporting printers on the LAN.
  • Amarok v2: automagically finds all DAAP-shares on the LAN (iTunes, for example). The bad news is: iTunes v7 and newer weren't yet reverse-engineered, so amarok cannot login to the most popular DAAP servers. Apple, why won't you give us a hand?
  • Pulseaudio: using the paprefs program, you can choose to share your sound devices and become zeroconf-discoverable. This means that people running the padevchooser program can find your sound card and redirect audio to/from yours.
    • It seems to require a wide bandwidth (couldn't find an option to lower the sound quality)
    • I've experienced some bugs which required restarting pulseaudio and other voodoo, in order to make things work.