Pulse Audio

Filed under: Geekiness — iain @ 15:30:32

Fedora 8, which I’d installed on my new Mac Mini, ships with Pulse Audio, a network sound system which uses ALSA at the business end and which runs as a drop-in replacement for ESounD.

Unfortunately in true Fedora tradition the initial implementation is somewhat broken. There are no manpages. There’s no init script to launch the sound server as a system-wide service. Non-root users (and if you do enable the system service manually it runs as a non-root user) can’t actually access the hardware because the /dev entries have root-only permissions. And some of the configuration tools aren’t installed by default, though the word on the street is that this has been fixed.

Eventually I managed to get it working.

Device permissions

Running the sound server as a system-wide daemon, which I wanted to do, requires that the user pulse be able to write to /dev/snd/*, /dev/dsp and /dev/mixer. I gave up on a Fedora-approved way and put lines in /etc/rc.d/rc.local to make these 660 and owned by root with group pulse.

Local permissions

The sound daemon won’t allow connections from the local host (and hence won’t be much use) unless you change these lines in /etc/pulse/default.pa. The bits to add are in italics.

    ### Load several protocols
    load-module module-esound-protocol-unix auth-anonymous=1
    load-module module-native-protocol-unix auth-anonymous=1

Network permissions

You can have one sound server for the whole network. This is splendid for me as I can have my virtual machines and audio-less servers using it if necessary. But by default network access is denied. Once again /etc/pulse/default.pa is the file to change.

    ### Network access (may be configured with paprefs, so leave this commented
    ### here if you plan to use paprefs)
    load-module module-esound-protocol-tcp auth-ip-acl=
    load-module module-native-protocol-tcp auth-ip-acl=
    #load-module module-zeroconf-publish

Hardware support

The heavy lifting is done by ALSA. Fedora has nice hardware autodetection and everything Just Worked for me since my Mac Mini’s soundcard was recognised by the HAL module. One thing I did have to do was unmute everything using:

    # alsaunmute

And then save the settings with:

    # alsactl store

Most people probably wouldn’t have to do anything here.

Starting the sound daemon

With no init script (tsk tsk, Red Hat), I had to slap a line into /etc/rc.d/rc.local to start the server on a system-wide basis. It seems Red Hat want users to start the server on-demand. That isn’t what I want at all.

    pulseaudio -D --system

The daemon complained that the user pulse didn’t have /var/run/pulse as its home directory, so I changed that. I also commented out the line trying to load module-x11-publish in default.pa as the server refused to start without an X11 display. YMMV.

Connecting over the network

On other Pulse Audio-aware systems you simply need to edit /etc/pulse/client.conf to reference the sound-playing machine.

    default-server = macmini

Fedora 7 configuration

My Fedora 7 virtual machines don’t have Pulse Audio as Fedora 7 has ESounD. To get things working I had to:

    # rpm -e esound
    # yum install alsa-plugins-pulseaudio
    # yum install pulseaudio-esound-compat
    # yum install puleaudio-utils

With the client configuration mentioned above I was then able to play sounds through the Mac Mini from a virtual machine.

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