user7922: I have a problem with my Arduino Uno board. It's not mounting in my Linux machine, but its power is on and the LED light is glowing. It was working before. After I tested buttons with an 12 V external supply, I am facing this scenario.
I tried lsusb and I checked /dev/ ports. Also, I couldn't find `ttyACM. I tried with another Arduino board and it's working. I think the board is gone, and I need help to fix this problem.
I thought it was a bootloader problem, and I got a new ATmega328P chip board. It is getting power on and the LED is blinking, but the port is not mounted. I tried with lsusb and also ls /dev/ttyACM* with no result.

user4531: You could try to flash the firmware of the USB controller.
General steps for Arduino R3 are:

Put the Arduino in DFU mode (the R3 does not require soldering for that)
Flash the firmware using:
dfu-programmer atmega16u2 erase
dfu-programmer atmega16u2 flash Arduino-usbserial-atmega16u2-Uno-Rev3.hex
dfu-programmer atmega16u2 reset

The package "dfu-programmer" is most likely available for your distribution.

If you have to build it from source, because your DFU programmer does not know the ATmega16U2 yet, you will need to install libusb-dev (on Debian-based systems).
Useful links for that:

Resetting your Uno R3's default firmware
Updating the Atmega8U2 and 16U2 on an Uno or Mega2560 using DFU

A useful search term for that is Arduino R3 DFU-programmer.

7922: <p>I have a problem with my Arduino Uno board. It's not mounting in my Linux machine, but its power is <em>on</em> and the LED light is glowing. It was working before. After I tested buttons with an 12&nbsp;V external supply, I am facing this scenario.</p>

<p>I tried <code>lsusb</code> and I checked <code>/dev/ ports</code>. Also, I couldn't find `ttyACM. I tried with another Arduino board and it's working. I think the board is gone, and I need help to fix this problem.</p>

<p>I thought it was a bootloader problem, and I got a <em>new ATmega328P chip board</em>. It is getting power on and the LED is blinking, but the port is not mounted. I tried with <code>lsusb</code> and also <code>ls /dev/ttyACM*</code> with no result.</p>
 4531: <p>You could try to flash the firmware of the USB controller.</p>

<p>General steps for Arduino R3 are:</p>

<ol>
<li><p>Put the Arduino in DFU mode (the R3 does <em>not</em> require soldering for that)</p></li>
<li><p>Flash the firmware using:</p>

<pre><code>dfu-programmer atmega16u2 erase
dfu-programmer atmega16u2 flash Arduino-usbserial-atmega16u2-Uno-Rev3.hex
dfu-programmer atmega16u2 reset
</code></pre>

<p>The package "dfu-programmer" is most likely available for your distribution.</p></li>
</ol>

<p>If you have to build it from source, because your DFU programmer does not know the ATmega16U2 yet, you will need to install libusb-dev (on Debian-based systems).</p>

<p>Useful links for that:</p>

<ul>
<li><em><a href="https://github.com/leocadiotine/Dvorany/wiki/Resetting-your-Uno-R3%27s-default-firmware" rel="nofollow noreferrer">Resetting your Uno R3's default firmware</a></em></li>
<li><em><a href="http://arduino.cc/en/Hacking/DFUProgramming8U2" rel="nofollow noreferrer">Updating the Atmega8U2 and 16U2 on an Uno or Mega2560 using DFU</a></em></li>
</ul>

<p>A useful search term for that is <code>Arduino R3 DFU-programmer</code>.</p>
