[Решено] Молчит линейный аудиовход. Не знаю с какого конца браться...

$ arecord -f dat -D hw:0,0 > z.wav
arecord: main:722: audio open error: Устройство или ресурс занято

$ amixer
Simple mixer control 'Master',0
  Capabilities: pvolume pvolume-joined pswitch pswitch-joined
  Playback channels: Mono
  Limits: Playback 0 - 42
  Mono: Playback 42 [100%] [0.00dB] [on]
Simple mixer control 'Headphone',0
  Capabilities: pvolume pswitch
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 42
  Mono:
  Front Left: Playback 42 [100%] [0.00dB] [on]
  Front Right: Playback 42 [100%] [0.00dB] [on]
Simple mixer control 'PCM',0
  Capabilities: pvolume
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 255
  Mono:
  Front Left: Playback 255 [100%] [0.00dB]
  Front Right: Playback 255 [100%] [0.00dB]
Simple mixer control 'Front',0
  Capabilities: pvolume pswitch
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 42
  Mono:
  Front Left: Playback 42 [100%] [0.00dB] [on]
  Front Right: Playback 42 [100%] [0.00dB] [on]
Simple mixer control 'Front Mic',0
  Capabilities: pvolume pswitch cswitch cswitch-joined cswitch-exclusive
  Capture exclusive group: 0
  Playback channels: Front Left - Front Right
  Capture channels: Mono
  Limits: Playback 0 - 31
  Mono: Capture [off]
  Front Left: Playback 27 [87%] [6.00dB] [on]
  Front Right: Playback 27 [87%] [6.00dB] [on]
Simple mixer control 'Front Mic Boost',0
  Capabilities: volume
  Playback channels: Front Left - Front Right
  Capture channels: Front Left - Front Right
  Limits: 0 - 3
  Front Left: 3 [100%] [30.75dB]
  Front Right: 3 [100%] [30.75dB]
Simple mixer control 'Surround',0
  Capabilities: pvolume pswitch
  Playback channels: Front Left - Front Right
  Limits: Playback 0 - 42
  Mono:
  Front Left: Playback 42 [100%] [0.00dB] [on]
  Front Right: Playback 42 [100%] [0.00dB] [on]
Simple mixer control 'Center',0
  Capabilities: pvolume pvolume-joined pswitch pswitch-joined
  Playback channels: Mono
  Limits: Playback 0 - 42
  Mono: Playback 42 [100%] [0.00dB] [on]
Simple mixer control 'LFE',0
  Capabilities: pvolume pvolume-joined pswitch pswitch-joined
  Playback channels: Mono
  Limits: Playback 0 - 42
  Mono: Playback 42 [100%] [0.00dB] [on]
Simple mixer control 'Line',0
  Capabilities: pvolume pswitch cswitch cswitch-joined cswitch-exclusive
  Capture exclusive group: 0
  Playback channels: Front Left - Front Right
  Capture channels: Mono
  Limits: Playback 0 - 31
  Mono: Capture [on]
  Front Left: Playback 26 [84%] [4.50dB] [on]
  Front Right: Playback 26 [84%] [4.50dB] [on]
Simple mixer control 'Capture',0
  Capabilities: cvolume cswitch
  Capture channels: Front Left - Front Right
  Limits: Capture 0 - 31
  Front Left: Capture 31 [100%] [30.00dB] [on]
  Front Right: Capture 31 [100%] [30.00dB] [on]
Simple mixer control 'Channel Mode',0
  Capabilities: enum
  Items: '2ch' '4ch' '6ch'
  Item0: '4ch'
Simple mixer control 'Digital',0
  Capabilities: cvolume
  Capture channels: Front Left - Front Right
  Limits: Capture 0 - 120
  Front Left: Capture 120 [100%] [30.00dB]
  Front Right: Capture 120 [100%] [30.00dB]
Simple mixer control 'Dynamic Power-Control',0
  Capabilities: enum
  Items: 'Disabled' 'Enabled'
  Item0: 'Enabled'
Simple mixer control 'Independent HP',0
  Capabilities: enum
  Items: 'Disabled' 'Enabled'
  Item0: 'Disabled'
Simple mixer control 'Loopback Mixing',0
  Capabilities: enum
  Items: 'Disabled' 'Enabled'
  Item0: 'Disabled'
Simple mixer control 'Rear Mic',0
  Capabilities: pvolume pswitch cswitch cswitch-joined cswitch-exclusive
  Capture exclusive group: 0
  Playback channels: Front Left - Front Right
  Capture channels: Mono
  Limits: Playback 0 - 31
  Mono: Capture [off]
  Front Left: Playback 0 [0%] [-34.50dB] [on]
  Front Right: Playback 0 [0%] [-34.50dB] [on]
Simple mixer control 'Rear Mic Boost',0
  Capabilities: volume
  Playback channels: Front Left - Front Right
  Capture channels: Front Left - Front Right
  Limits: 0 - 3
  Front Left: 3 [100%] [30.75dB]
  Front Right: 3 [100%] [30.75dB]
Simple mixer control 'Stereo Mix',0
  Capabilities: cswitch cswitch-joined cswitch-exclusive
  Capture exclusive group: 0
  Capture channels: Mono
  Mono: Capture [off]

$ amixer sget 'Line' 90%
Simple mixer control 'Line',0
  Capabilities: pvolume pswitch cswitch cswitch-joined cswitch-exclusive
  Capture exclusive group: 0
  Playback channels: Front Left - Front Right
  Capture channels: Mono
  Limits: Playback 0 - 31
  Mono: Capture [on]
  Front Left: Playback 31 [100%] [12.00dB] [on]
  Front Right: Playback 31 [100%] [12.00dB] [on]

$ amixer set 'Channel Mode' 2ch

libpulse /usr/bin/pacat
libpulse /usr/bin/pactl
libpulse /usr/bin/padsp
libpulse /usr/bin/pamon
libpulse /usr/bin/paplay
libpulse /usr/bin/parec
libpulse /usr/bin/parecord