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Lennart Poettering 2004-09-23 23:26:15 +00:00
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@ -62,14 +62,34 @@
embed Polypaudio in the aRts process.</p></li>
<li><p><b>I often hear noises when playing back with Polypaudio, what can I do?</b></p>
<p>There are to possible solutions: either make the polypaudio
binary SUID root (<tt>chmod u+s /usr/bin/polypaudio</tt>) and run it
with argument <tt>--high-priority=1</tt> or increase the fragment sizes of the audio
<p>There are to possible solutions: run polypaudio with argument
<tt>--high-priority=1</tt> and make yourself member of the group
<tt>realtime</tt>, or increase the fragment sizes of the audio
drivers. The former will allow Polypaudio to activate
<tt>SCHED_FIFO</tt> high priority scheduling (root rights are dropped
immediately after this) Keep in mind that is a potential security hole!</p></li>
immediately after this) Keep in mind that this is a potential security hole!</p></li>
<li><p><b>I only want to run polypaudio when it is needed, how do I do this?</b></p>
<li><p><b>The <tt>polypaudio</tt> executable is installed SUID root by default. Why this? Isn't this a potential security hole?</b></p>
<p>Polypaudio activates <tt>SCHED_FIFO</tt> scheduling if the user
passes <tt>--high-priority=1</tt>. This will only succeed when
executed as root, therefore the binary is marked SUID root by
default. Yes, this is a potential security hole. However, polypaudio
tries its best to minimize the security threat: immediately after
startup polypaudio drops all capabilities except
<tt>CAP_SYS_NICE</tt> (At least on systems that support it, like Linux; see <tt>man 7
capabilities</tt> for more information). If the calling user is not a
member of the group <tt>realtime</tt> (which is required to have a GID
< 1000), root rights are dropped immediately. This means, you can
install polypaudio SUID root, but only a subset of your users (the
members of the group <tt>realtime</tt>) may make use of realtime
scheduling. Keep in mind that these users might load their own binary
modules into the polypaudio daemon which may freeze the machine. The
daemon has a minimal protection against CPU hogging (the daemon is
killed after hogging more than 70% CPU for 5 seconds), but this may
be circumvented easily by evildoers.</p></li>
<li><p><b>I want to run polypaudio only when it is needed, how do I do this?</b></p>
<p>Set <tt>autospawn = yes</tt> in <tt>client.conf</tt>. That
configuration file may be found either in <tt>/etc/polypaudio/</tt> or
@ -81,12 +101,35 @@ in <tt>~/.polypaudio/</tt>.</p></li>
<p>Add <tt>-v</tt> for terse usage instructions.</p>
<li><p><b>What environment does polypaudio care about?</b></p>
<li><p><b>How do I use polypaudio over the network?</b></p>
<p>Just set <tt>$POLYP_SERVER</tt> to the host name of the polypaudio server.</p>
<li><p><b>Is polypaudio capable of providing synchronized audio playback over the network for movie players like <tt>mplayer</tt>?</b></p>
<p>Yes! Unless your network is congested in some way (i.e. transfer latencies vary strongly) it works perfectly. Drop me an email for experimental patches for MPlayer.</p>
<li><p><b>What environment variables does polypaudio care about?</b></p>
<p>The client honors: <tt>POLYP_SINK</tt> (default sink to connect to), <tt>POLYP_SOURCE</tt> (default source to connect to), <tt>POLYP_SERVER</tt> (default server to connect to, like <tt>ESPEAKER</tt>), <tt>POLYP_BINARY</tt> (the binary to start when autospawning a daemon), <tt>POLYP_CLIENTCONFIG</tt> (path to the client configuration file).</p>
<p>The daemon honors: <tt>POLYP_SCRIPT</tt> (default CLI script file run after startup), <tt>POLYP_CONFIG</tt> (default daemon configuration file), <tt>POLYP_DLPATH</tt> (colon separated list of paths where to look for modules)</p></li>
<li><p><b>I saw that SIGUSR2 provokes loading of the module <tt>module-cli-protocol-unix</tt>. But how do I make use of that?</b></p>
<p>A brilliant guy named Lennart Poettering once wrote a nifty tool
for that purpose: <a
href="http://0pointer.de/lennart/projects/bidilink/">bidilink</a>. To
connect to a running polypaudio daemon try using the following commands:</p>
<pre>killall -USR2 polypaudio
bidilink unix-client:/tmp/polypaudio/cli</pre>
<p><i>BTW: Someone should package that great tool for Debian!</i></p>
</li>
</ol>
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