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>-r</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).</p></li>
+ immediately after this) Keep in mind that this is a potential security hole!</p></li>
+
+ <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
+in <tt>~/.polypaudio/</tt>.</p></li>
+
+ <li><p><b>How do I list all polypaudio modules installed?</b></p>
+
+ <p><tt>polypaudio --dump-modules</tt></p>
+
+ <p>Add <tt>-v</tt> for terse usage instructions.</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>
+
+
+<p><b>New:</b> There's now a tool <tt>pacmd</tt> that automates sending SIGUSR2 to the daemon and running a bidilink like tool for you.</p>
+</li>
+
+<li><p><b>How do the polypaudio libraries decide where to connect to?</b></p>
+<p>The following rule applies:</p>
+<ol>
+ <li>If the the application using the library specifies a server to connect to it is used. If the connection fails, the library fails too.</li>
+ <li>If the environment variable <tt>POLYP_SERVER</tt> is defined the library connects to that server. If the connection fails, the library fails too.</li>
+ <li>If <tt>$DISPLAY</tt> is set, the library tries to connect to that server and looks for the root window property <tt>POYLP_SERVER</tt> for the host to connect to. If <tt>POLYP_COOKIE</tt> is set it is used as authentication cookie.</li>
+ <li>If the client configuration file (<tt>~/.polypaudio/client.conf</tt> or <tt>/etc/polypaudio/client.conf</tt>) sets the server address, the library connects to that server. If the connection fails, the library fails too.</li>
+ <li>The library tries to connect to the default local UNIX socket for polypaudio servers. If the connection fails, it proceeds with the next item.</li>
+ <li>The library tries to connect to the default local TCP socket for polypaudio servers. If the connection fails, it proceeds with the next item.</li>
+ <li>If <tt>$DISPLAY</tt> is set, the library tries to connect to the default TCP port of that host. If the connection fails, it proceeds with the next item.</li>
+ <li>The connection fails.</li>
+</ol>
+</li>
+
+<li><p><b>Why the heck does libpolyp link against libX11?</b></p>
+<p>The Polypaudio client libraries look for some X11 root window properties for the credentials of the Polypaudio server to access. You may compile Polypaudio without X11 for disabling this.</p></li>
</ol>