For some reason, with the upgrade from
1.9.8~dfsg.4+20120529git007cdc37-5, jack_control start no longer
works, and I get this:

Sun Jun 23 19:44:26 2013: Controller activated. Version 1.9.10 (unknown) built on Sat Jun 22 10:42:33 2013
Sun Jun 23 19:44:26 2013: Loading settings from "/home/jamie/.config/jack/conf.xml" using expat_2.1.0 ...
Sun Jun 23 19:44:26 2013: setting parameter 'engine':'driver':'(null)' to value "alsa"
Sun Jun 23 19:44:26 2013: setting parameter 'engine':'realtime':'(null)' to value "true"
Sun Jun 23 19:44:26 2013: setting parameter 'drivers':'alsa':'capture' to value "1"
Sun Jun 23 19:44:26 2013: setting parameter 'drivers':'alsa':'playback' to value "1"
Sun Jun 23 19:44:26 2013: setting parameter 'drivers':'alsa':'device' to value "bithead"
Sun Jun 23 19:44:26 2013: setting parameter 'drivers':'alsa':'nperiods' to value "3"
Sun Jun 23 19:44:26 2013: setting parameter 'drivers':'alsa':'dither' to value "s"
Sun Jun 23 19:44:26 2013: Listening for D-Bus messages
Sun Jun 23 19:44:26 2013: Starting jack server...
Sun Jun 23 19:44:26 2013: JACK server starting in realtime mode with priority 10
Sun Jun 23 19:44:27 2013: ERROR: control open "1" (No such file or directory)
Sun Jun 23 19:44:27 2013: ERROR: control open "1" (No such file or directory)
Sun Jun 23 19:44:27 2013: creating alsa driver ... 1|1|1024|3|48000|0|0|nomon|swmeter|-|32bit
Sun Jun 23 19:44:27 2013: ERROR: control open "1" (No such file or directory)
Sun Jun 23 19:44:27 2013: ERROR: ALSA: Cannot open PCM device alsa_pcm for playback. Falling back to capture-only mode
Sun Jun 23 19:44:27 2013: ERROR: Cannot initialize driver
Sun Jun 23 19:44:27 2013: ERROR: JackServer::Open failed with -1
Sun Jun 23 19:44:27 2013: ERROR: Failed to open server


Instead of:

Sun Jun 23 20:15:27 2013: Controller activated. Version 1.9.9 (unknown) built on Tue Nov 27 20:48:57 2012
Sun Jun 23 20:15:27 2013: Loading settings from "/home/jamie/.config/jack/conf.xml" using expat_2.1.0 ...
Sun Jun 23 20:15:27 2013: setting parameter 'engine':'driver':'(null)' to value "alsa"
Sun Jun 23 20:15:27 2013: setting parameter 'engine':'realtime':'(null)' to value "true"
Sun Jun 23 20:15:27 2013: setting parameter 'drivers':'alsa':'capture' to value "1"
Sun Jun 23 20:15:27 2013: setting parameter 'drivers':'alsa':'playback' to value "1"
Sun Jun 23 20:15:27 2013: setting parameter 'drivers':'alsa':'device' to value "bithead"
Sun Jun 23 20:15:27 2013: setting parameter 'drivers':'alsa':'nperiods' to value "3"
Sun Jun 23 20:15:27 2013: setting parameter 'drivers':'alsa':'dither' to value "s"
Sun Jun 23 20:15:27 2013: Listening for D-Bus messages
Sun Jun 23 20:15:27 2013: Starting jack server...
Sun Jun 23 20:15:27 2013: JACK server starting in realtime mode with priority 10
Sun Jun 23 20:15:27 2013: Acquired audio card Audio1
Sun Jun 23 20:15:27 2013: creating alsa driver ... bithead|bithead|1024|3|48000|0|0|nomon|swmeter|-|32bit
Sun Jun 23 20:15:27 2013: configuring for 48000Hz, period = 1024 frames (21.3 ms), buffer = 3 periods
Sun Jun 23 20:15:27 2013: ALSA: final selected sample format for capture: 16bit little-endian
Sun Jun 23 20:15:27 2013: ALSA: use 3 periods for capture
Sun Jun 23 20:15:27 2013: ALSA: final selected sample format for playback: 16bit little-endian
Sun Jun 23 20:15:27 2013: ALSA: use 3 periods for playback
Sun Jun 23 20:15:27 2013: Noise-shaped dithering at 16 bits
Sun Jun 23 20:15:27 2013: graph reorder: new port 'system:capture_1'
Sun Jun 23 20:15:27 2013: New client 'system' with PID 0
Sun Jun 23 20:15:27 2013: graph reorder: new port 'system:capture_2'
Sun Jun 23 20:15:27 2013: graph reorder: new port 'system:playback_1'
Sun Jun 23 20:15:27 2013: graph reorder: new port 'system:playback_2'


Without having delved into it in any detail, it looks like the new
build doesn't interpret my config correctly.  My conf.xml is:

<?xml version="1.0"?>
<!--
JACK settings, as persisted by D-Bus object.
You probably don't want to edit this because
it will be overwritten next time jackdbus saves.
-->
<!-- Mon Dec 10 06:49:11 2012 -->
<jack>
 <engine>
  <option name="driver">alsa</option>
  <option name="realtime">true</option>
 </engine>
 <drivers>
  <driver name="alsarawmidi">
  </driver>
  <driver name="net">
  </driver>
  <driver name="alsa">
   <option name="capture">1</option>
   <option name="playback">1</option>
   <option name="device">bithead</option>
   <option name="nperiods">3</option>
   <option name="dither">s</option>
  </driver>
  <driver name="loopback">
  </driver>
  <driver name="netone">
  </driver>
  <driver name="dummy">
  </driver>
 </drivers>
 <internals>
  <internal name="profiler">
  </internal>
  <internal name="netadapter">
  </internal>
  <internal name="audioadapter">
  </internal>
  <internal name="netmanager">
  </internal>
 </internals>
</jack>

OK, probably related to commit cb88917543e23aa1a5365d131eac8ac6bcbfb975
upstream.

Now, I don't remember having ever *explicitly* set the capture and
playback ALSA driver params and I've been running the same config for
some years, with the last change made back in December and that was
just switching to shaped dithering.  If I unset those params, then
things work fine again.  I have to wonder if older versions of
jack2 serialized its config options differently and that's how I got
   <option name="capture">1</option>
   <option name="playback">1</option>
in my conf.xml ... if so, I probably won't be the only person who sees
this issue pop up.