user26792: The error message is:

avrdude: AVR device initialized and ready to accept instructions
  avrdude: Device signature = 0x1e950f
  avrdude: Expected signature for ATmega32U4 is 1E 95 87
  Double check chip, or use -F to override this check.  

This error message is thrown when I attempt to upload any program to the Yun shield through an Arduino Bridge between the Uno and Yun shield with the Uno’s ATMega32 shorted into reset mode.
Any advice on how to get this working? Thanks.

user23841: Apparently there is no ATMega32U4 on that board but ATmega328P according to the signature 0x1e950f.
Anyway, you may have to change or add new board with correct MCU setting.
Now I can see the difference between Yun and Yun shield. Shield can be connected to any Arduino board and Yun is similar like Shield + Leonardo.
I've found board definition for Arduino UNO:
unoyun.name=Arduino Uno -- Dragino Yún
unoyun.upload.via_ssh=true

unoyun.vid.0=0x2341
unoyun.pid.0=0x0043
unoyun.vid.1=0x2341
unoyun.pid.1=0x0001
unoyun.upload.tool=avrdude
unoyun.upload.protocol=arduino
unoyun.upload.maximum_size=32256
unoyun.upload.maximum_data_size=2048
unoyun.upload.speed=57600
unoyun.upload.disable_flushing=true
unoyun.upload.use_1200bps_touch=true
unoyun.upload.wait_for_upload_port=true

unoyun.bootloader.tool=avrdude
unoyun.bootloader.low_fuses=0xff
unoyun.bootloader.high_fuses=0xde
unoyun.bootloader.extended_fuses=0x05
unoyun.bootloader.file=optiboot/optiboot_atmega328.hex
unoyun.bootloader.unlock_bits=0x3F
unoyun.bootloader.lock_bits=0x0F

unoyun.build.mcu=atmega328p
unoyun.build.f_cpu=16000000L
unoyun.build.board=AVR_YUN
unoyun.build.core=arduino
unoyun.build.variant=standard

More info about it here: https://www.arduino.cc/en/Guide/ArduinoYunShield or similar product http://wiki.dragino.com/index.php?title=Yun_Shield

user29657: Make sure the board selected in the Yun Shield is the correct one (in this case Arduino UNO).
Steps for selecting the board on the Yun Shield

In your web browser load the Yun Shield page and log in (how to do this is described in the Quick Start Guide).
Click on the SENSORS menu button.
Under Arduino Board Type select the correct one.
Click on the CONFIGURE & RESTART MCU button to apply settings.
Maybe manual restart of the board would be needed (power unplug).



26792: <p>The error message is:</p>

<blockquote>
  <p>avrdude: AVR device initialized and ready to accept instructions<br>
  avrdude: Device signature = 0x1e950f<br>
  avrdude: Expected signature for ATmega32U4 is 1E 95 87<br>
  Double check chip, or use -F to override this check.  </p>
</blockquote>

<p>This error message is thrown when I attempt to upload any program to the Yun shield through an Arduino Bridge between the Uno and Yun shield with the Uno’s ATMega32 shorted into reset mode.<br>
Any advice on how to get this working? Thanks.</p>
 23841: <p>Apparently there is no <code>ATMega32U4</code> on that board but <code>ATmega328P</code> according to the signature <code>0x1e950f</code>.</p>

<p>Anyway, you may have to change or add new board with correct MCU setting.</p>

<p>Now I can see the difference between Yun and Yun shield. Shield can be connected to any Arduino board and Yun is similar like Shield + Leonardo.</p>

<p>I've found board definition for Arduino UNO:</p>

<pre><code>unoyun.name=Arduino Uno -- Dragino Yún
unoyun.upload.via_ssh=true

unoyun.vid.0=0x2341
unoyun.pid.0=0x0043
unoyun.vid.1=0x2341
unoyun.pid.1=0x0001
unoyun.upload.tool=avrdude
unoyun.upload.protocol=arduino
unoyun.upload.maximum_size=32256
unoyun.upload.maximum_data_size=2048
unoyun.upload.speed=57600
unoyun.upload.disable_flushing=true
unoyun.upload.use_1200bps_touch=true
unoyun.upload.wait_for_upload_port=true

unoyun.bootloader.tool=avrdude
unoyun.bootloader.low_fuses=0xff
unoyun.bootloader.high_fuses=0xde
unoyun.bootloader.extended_fuses=0x05
unoyun.bootloader.file=optiboot/optiboot_atmega328.hex
unoyun.bootloader.unlock_bits=0x3F
unoyun.bootloader.lock_bits=0x0F

unoyun.build.mcu=atmega328p
unoyun.build.f_cpu=16000000L
unoyun.build.board=AVR_YUN
unoyun.build.core=arduino
unoyun.build.variant=standard
</code></pre>

<p>More info about it here: <a href="https://www.arduino.cc/en/Guide/ArduinoYunShield" rel="nofollow">https://www.arduino.cc/en/Guide/ArduinoYunShield</a> or similar product <a href="http://wiki.dragino.com/index.php?title=Yun_Shield" rel="nofollow">http://wiki.dragino.com/index.php?title=Yun_Shield</a></p>
 29657: <p>Make sure the board selected in the <em>Yun Shield</em> is the correct one (in this case <em>Arduino UNO</em>).</p>

<h2>Steps for selecting the board on the Yun Shield</h2>

<ol>
<li>In your web browser load the <em>Yun Shield</em> page and log in (how to do this is described in the <a href="http://www.dragino.com/downloads/downloads/YunShield/YUN_SHIELD_QUICK_START_GUIDE_v1.0.pdf" rel="nofollow noreferrer">Quick Start Guide</a>).</li>
<li>Click on the SENSORS menu button.</li>
<li>Under <em>Arduino Board Type</em> select the correct one.</li>
<li>Click on the <em>CONFIGURE &amp; RESTART MCU</em> button to apply settings.</li>
<li>Maybe manual restart of the board would be needed (power unplug).</li>
</ol>

<p><a href="https://i.stack.imgur.com/vutkA.gif" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/vutkA.gif" alt="enter image description here"></a></p>
