user8534: I have an Arduino Uno which communicated with the computer (Ubunutu 14.04) fine till 6 days ago (I assume some software update is to blame).
Now when trying to upload I get
processing.app.SerialNotFoundException: Serial port '/dev/ttyACM0' not found. Did you select the right one from the Tools > Serial Port menu?   at processing.app.Serial.(Serial.java:191)    at processing.app.Serial.(Serial.java:77)     at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:77)    at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:175)   at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:67)     at processing.app.Sketch.upload(Sketch.java:1671)   at processing.app.Sketch.exportApplet(Sketch.java:1627)     at processing.app.Sketch.exportApplet(Sketch.java:1599)     at processing.app.Editor$DefaultExportHandler.run(Editor.java:2380)     at java.lang.Thread.run(Thread.java:745)
When I sudo ls /dev/ttyA*
I get
ls: cannot access /dev/ttyA*: No such file or directory

So it does not look like a permission issue.
when I lsusb
I get
Bus 001 Device 002: ID 8087:8000 Intel Corp. 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 002 Device 003: ID 04f2:b39a Chicony Electronics Co., Ltd 
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

So it does not even see the device (which is connected and pulling current).
when I dmesg before and after connecting the Arduino, I don't see anything new.
I tried switching USB cables, and switching USB ports on the machine (both ports work with a mouse), but in vain.
What went wrong and how do I fix it ?
Thanks,
David.

user4143: Ok, it sounds like there is an issue with the ATMega(8/16)U2 chip or its surroundings.  It might just need its firmware refreshing (which can be done with another Arduino as a programmer) or it might be plain dead.
Another possibility is the USB socket itself.  I have two UNOs, one which is perfectly fine, and one where I need to hold the cable at just the right angle for it to connect properly.  You can try using a fine needle to try and raise the four metal strips in the USB connector a fraction to make better contact.

8534: <p>I have an Arduino Uno which communicated with the computer (Ubunutu 14.04) fine till 6 days ago (I assume some software update is to blame).</p>

<p>Now when trying to upload I get</p>

<p>processing.app.SerialNotFoundException: Serial port '/dev/ttyACM0' not found. Did you select the right one from the Tools > Serial Port menu?   at processing.app.Serial.(Serial.java:191)    at processing.app.Serial.(Serial.java:77)     at processing.app.debug.Uploader.flushSerialBuffer(Uploader.java:77)    at processing.app.debug.AvrdudeUploader.uploadViaBootloader(AvrdudeUploader.java:175)   at processing.app.debug.AvrdudeUploader.uploadUsingPreferences(AvrdudeUploader.java:67)     at processing.app.Sketch.upload(Sketch.java:1671)   at processing.app.Sketch.exportApplet(Sketch.java:1627)     at processing.app.Sketch.exportApplet(Sketch.java:1599)     at processing.app.Editor$DefaultExportHandler.run(Editor.java:2380)     at java.lang.Thread.run(Thread.java:745)</p>

<p>When I sudo ls /dev/ttyA*</p>

<p>I get</p>

<pre><code>ls: cannot access /dev/ttyA*: No such file or directory
</code></pre>

<p>So it does not look like a permission issue.</p>

<p>when I lsusb</p>

<p>I get</p>

<pre><code>Bus 001 Device 002: ID 8087:8000 Intel Corp. 
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 003 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 002 Device 003: ID 04f2:b39a Chicony Electronics Co., Ltd 
Bus 002 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
</code></pre>

<p>So it does not even see the device (which is connected and pulling current).</p>

<p>when I dmesg before and after connecting the Arduino, I don't see anything new.</p>

<p>I tried switching USB cables, and switching USB ports on the machine (both ports work with a mouse), but in vain.</p>

<p>What went wrong and how do I fix it ?</p>

<p>Thanks,
David.</p>
 4143: <p>Ok, it sounds like there is an issue with the ATMega(8/16)U2 chip or its surroundings.  It might just need its firmware refreshing (which can be done with another Arduino as a programmer) or it might be plain dead.</p>

<p>Another possibility is the USB socket itself.  I have two UNOs, one which is perfectly fine, and one where I need to hold the cable at just the right angle for it to connect properly.  You can try using a fine needle to try and raise the four metal strips in the USB connector a fraction to make better contact.</p>
