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index 7a93d73..b5bf662 100644
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+++ b/homepage/knowledge/linux.html
@@ -16,7 +16,7 @@
 <SCRIPT SRC="/js/sheets.js"  TYPE="application/javascript"></SCRIPT>
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 <H1>linux</H1>
-<H3>updated 2022-04-23</H3>
+<H3>updated 2022-04-24</H3>
 <HR ALIGN="left" SIZE="1" WIDTH="25%" />
 <H2>ACPI client</H2>
 <P>
@@ -25,7 +25,6 @@ The usual text program used is <CODE>acpi(1)</CODE>.
 </P>
 
 <H2>Alpine</H2>
-<H3>Resources</H3>
 <UL>
 <LI><A HREF="https://pkgs.alpinelinux.org/contents">Alpine repositories content search</A></LI>
 </UL>
@@ -93,7 +92,6 @@ It's custom for Linux systems to have <CODE>make(1)</CODE> as GNU Make and <CODE
 </P>
 
 <H2>Mount LUKS encrypted partitions at boot</H2>
-<H3>Sources</H3>
 <UL>
 	<LI><A HREF="https://www.howtoforge.com/automatically-unlock-luks-encrypted-drives-with-a-keyfile/">Automatically Unlock LUKS Encrypted Drives With A Keyfile</A></LI>
 	<LI><A HREF="https://wiki.gentoo.org/wiki/Dm-crypt">Dm-crypt</A> (Gentoo Wiki)</LI>
@@ -127,7 +125,6 @@ Alpine by default uses <CODE>mandoc</CODE>.
 </P>
 
 <H2>Partitions and filesystems</H2>
-<H3>See also</H3>
 <UL>
 	<LI><A HREF="https://wiki.archlinux.org/title/EFI_system_partition">EFI system partition (Arch Wiki)</A></LI>
 	<LI><A HREF="https://wiki.artixlinux.org/Main/Installation#Partition_your_disk_.28BIOS.29">Installation#Partition your disk - Artix wiki</A></LI>
@@ -207,7 +204,6 @@ You'd be better off using <CODE>ed(1)</CODE>; the UX is very similar.
 </P>
 
 <H2>util-linux</H2>
-<H3>See also</H3>
 <UL>
 <LI><A HREF="https://en.wikipedia.org/wiki/Util-linux">util-linux - Wikipedia</A></LI>
 </UL>
@@ -228,7 +224,6 @@ I haven't had good luck with it but Alpine set it up automatically.
 </P>
 
 <H2>X</H2>
-<H3>Sources</H3>
 <UL>
 	<LI><A HREF="https://wiki.archlinux.org/title/Xorg">Xorg</A> (Arch Wiki)</LI>
 </UL>
@@ -237,6 +232,11 @@ X is a graphical windowing system that can be used on Linux, FreeBSD, OpenBSD, N
 X is not the only windowing system; <CODE>twin(1)</CODE> exists for windowed multitasking within a framebuffer and Wayland is another windowing system intended to replace X.
 </P>
 <P>
+Xorg requires the user to be a member of the <CODE>input</CODE> and <CODE>video</CODE> groups (or superuser), otherwise it won't be able to access the relevent device files.
+These errors look like <CODE>Failed to open /dev/input/event[<I>number</I>] (Permission denied)</CODE> when not in the <CODE>input</CODE> group
+and <CODE>Failed to open /dev/tty[<I>number</I>] (Permission denied)</CODE> when not in the <CODE>video</CODE> group.
+</P>
+<P>
 Some Linux software distributions have included scripts to automatically fetch and install an X server.
 Alpine has <CODE>setup-xorg-base</CODE>, which adds the packages <CODE>xorg-server</CODE>, <CODE>xf86-input-libinput</CODE>, <CODE>eudev</CODE>, and <CODE>mesa</CODE>, and then enables the OpenRC services for udev.
 </P>
@@ -256,5 +256,35 @@ the X resource database manager as <CODE>xorg-xrdb</CODE>,
 xset as <CODE>xorg-xset</CODE>,
 and xsetroot as <CODE>xorg-xsetroot</CODE>.
 </P>
+<P>Alpine has xinput as <CODE>xinput</CODE>.</P>
+
+<H3>Audio</H3>
+<P>
+Most audio servers recommend that they be run in userspace with user privileges, with PulseAudio going so far as to exiting when run as root without additional configuration.
+The Alpine wiki currently recommends <CODE>pipewire(1)</CODE>, with postmarketOS, which is based on Alpine, coming pre-configured with PipeWire.
+PipeWire is relatively new and the typical audio server used is PulseAudio; Debian and many popular Debian-based distributions come pre-configured with PulseAudio.
+</P>
+<H4>PipeWire</H4>
+<UL>
+<LI><A HREF="https://wiki.alpinelinux.org/wiki/PipeWire">PipeWire</A> (Alpine Linux Wiki)</LI>
+<LI><A HREF="https://gitlab.freedesktop.org/pipewire/pipewire/-/wikis/home">PipeWire</A> (FreeDesktop Wiki)</LI>
+</UL>
+<P>
+Provided by the <CODE>pipewire</CODE> package on Alpine.
+</P>
+<PRE>
+RTKit error: org.freedesktop.DBus.Error.ServiceUnknown
+</PRE>
+<P>
+This means you need <CODE>rtkit</CODE> installed and running through your initialization system.
+</P>
+<H4>PulseAudio</H4>
+<P>
+
+<H3>Media</H3>
+<P>
+<CODE>mpv(1)</CODE> and <CODE>vlc(1)</CODE> are good options.
+</P>
+
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