user28565: I'm trying to make my Arduino's LED blink for the first time, but when I try to upload the code I get the following error in the Serial Monitor:

Error opening serial port '/dev/ttyACM0'.
  Try consulting the documentation at http://playground.arduino.cc/Linux/All#Permission

BTW, I have serial.debug_rate=9600, so I don't think that's the problem. Can anyone help me with this please? 

user56630: That issue is due to your username not being in the dialout group.
Try: sudo usermod -a -G dialout yourusername and rebooting to load the changes, then check again if the problem still persists...
I wrote an article about that here: Solving Arduino IDE upload problem, and serial monitor error on Ubuntu.

user28084: It seems your serial does not have the right permissions to be opened in user mode. Try adjusting that by typing
sudo chmod a+rw /dev/ttyACM0

on the console (open it by CTRLALTT).

28565: <p>I'm trying to make my Arduino's LED blink for the first time, but when I try to upload the code I get the following error in the Serial Monitor:</p>

<blockquote>
  <p>Error opening serial port '/dev/ttyACM0'.<br>
  Try consulting the documentation at <a href="http://playground.arduino.cc/Linux/All#Permission" rel="nofollow noreferrer">http://playground.arduino.cc/Linux/All#Permission</a></p>
</blockquote>

<p>BTW, I have <code>serial.debug_rate=9600</code>, so I don't think that's the problem. Can anyone help me with this please? </p>
 56630: <p>That issue is due to your username not being in the dialout group.
Try: <code>sudo usermod -a -G dialout yourusername</code> and rebooting to load the changes, then check again if the problem still persists...</p>

<p>I wrote an article about that here: <a href="http://osrc.rip/Articles/SolvingArduinoUploadProblemOnLinux.html" rel="nofollow noreferrer">Solving Arduino IDE upload problem, and serial monitor error on Ubuntu</a>.</p>
 28084: <p>It seems your serial does not have the right permissions to be opened in <em>user mode</em>. Try adjusting that by typing</p>

<pre><code>sudo chmod a+rw /dev/ttyACM0
</code></pre>

<p>on the console (open it by <kbd>CTRL</kbd><kbd>ALT</kbd><kbd>T</kbd>).</p>
