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[Edit] Complete restatement of the problem:

My system freezes when I plug a memory device into a USB port. I have just upgraded from 18.04 LTS to 20.04 LTS. All of this hardware has worked without issue for months before the upgrade.

Symptoms of the freeze: Mouse cursor will move, cannot pick anything, no scrolling or right click. Keyboard doesn't respond. Alt-F2 will not bring up a terminal, cntrl-alt-T will not bring up a terminal. sysreq-alt-R-E-I-S-U-B will reboot. control-alt-F1 will log the user out. During a freeze, $top stops displaying new information. The clock freezes at the current time.

The freeze can be reliably initiated by:
plugging any of several thumbdrives into any USB port
plugging a particular microSD memory card into a USB memory card reader

The freeze does not initiate when

A Logitech Unifying reciever plugged into USB seems to have no problems.
Plugging one of several different thumb drives into the USB ports. plugging a different microSD card into a memory card reader.

I have two users set up. One of them is on "Desktop: Gnome" and "Session: Gnome-XORG", and has the freeze problem.

The other is on "Desktop: XDG_CURRENT_DESKTOP" and "Session: Ubuntu". This user does not experience the freeze problem.

I'm into stuff I don't really understand here so I don't know what the impact of that means.

I have: Uninstalled Nautilus, confirmed the problem happens when Nautilus isn't installed. Re-installed after sudo apt update and sudo apt upgrade

Removed Radeon video card and installed an Nvidia card, problem still occurs

Removed the memory sticks, tried installing them one at a time, problem still occurs

Done a BIOS memory and hardware test with no problems found.

[EDIT] I have Universe, Multiverse, and Restricted repositories enabled. So far all hardware tests and memory tests have checked out OK.

Here is some more information that may or may not be relevant:

sudo dmidecode -s bios-version A12

~$ free -h

              total        used        free      shared  buff/cache   available

Mem:           31Gi       3.1Gi        11Gi        73Mi        16Gi        27Gi

Swap: 2.0Gi 0B 2.0Gi

~$ ls -al /usr/share/gnome-shell/extensions total 20

drwxr-xr-x 5 root root 4096 Sep 29 12:56 .

drwxr-xr-x 7 root root 4096 Sep 29 12:59 ..


drwxr-xr-x 2 root root 4096 Sep 29 12:56 desktop-icons@csoriano


drwxr-xr-x 3 root root 4096 Sep 29 11:51 ubuntu-appindicators@ubuntu.com


drwxr-xr-x 3 root root 4096 Sep 29 11:51 ubuntu-dock@ubuntu.com

~$ lspci | grep VGA Thrice 03:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] R600 [Radeon HD 2900 PRO/XT]

Invention1
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  • Well, I have been using some of the techniques there to try to reboot, but it has not shed any light on how to troubleshoot. Thanks. – Invention1 Sep 30 '20 at 03:09
  • That will kill the monitor, will it not? I'm not understanding how I will see the monitor with the graphics card is not plugged in - am I missing something? Are you indicating I should plug in a VGA cable to the motherboard? – Invention1 Sep 30 '20 at 03:29
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    Well it turns out that's a serial port on the MB,[D'oh] but I found an old Nvidia Gforce card, which should use completely different drivers. Puilled out the Radeon video card entirely. Will try to stimulate the issue again, report back in a minute. – Invention1 Sep 30 '20 at 03:55
  • If that doesn't work the next step to troubleshoot is to try jiggling the RAM sticks or take them out one at a time and test if it freezes without the removed RAM stick. – karel Sep 30 '20 at 04:01
  • Verified I can cause the problem with an Nvidia Geforce graphics card as well as the original Radeon graphics card. It happens every time I plug in a thumb drive. Nautilus is acting slow and odd, I'm suspecting it is some problem with Nautilus. I have uninstalled and reinstalled Nautilus to no avail. – Invention1 Sep 30 '20 at 04:02
  • Ok will start fiddling with RAM and see if that gets anywhere. Thanks for staying with this. – Invention1 Sep 30 '20 at 04:04
  • I verified that the problem persists with any one of the four RAM modules installed and the others unplugged. I've now put all the RAM back in and reinserted the original Radeon graphics card. – Invention1 Sep 30 '20 at 05:05
  • I ran memtester with no indication of errors, but it doesn't test everything. I will run memtest86 from the grub menu next. – Invention1 Sep 30 '20 at 05:15
  • Ran a Bios hardware test, which does memory tests, no errors detected. I don't think there's a hardware problem here. – Invention1 Sep 30 '20 at 11:39
  • Neither do I. . – karel Sep 30 '20 at 11:55

1 Answers1

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The problem seemed to be related to Gnome somehow. A user who was on Ubuntu:Gnome Desktop and Session Ubuntu did not experience the problem. A user who was on Desktop: Gnome and Session Gnome-Xorg did have the problem. The problem occurred on several USB memory devices but not all. It seemed the memory device was busy doing something (I never figured out what) that bogged down the system altogether.

Switching the user with the problem to Desktop: ubuntu:Gnome and Session: ubuntu seemed to make the problem dissappear. Here; 's the fix:

    printf 'Desktop: %s\nSession: %s\n' "$XDG_CURRENT_DESKTOP" "$GDMSESSION"
    Desktop: Gnome
    Session: Gnome-Xorg

The user above had the problem. On boot, at login there is a small gear icon at the bottom right corner of the screen (this icon dissappears later) that allows one to switch the user to a different Gnome. Picking "Ubuntu" changed the users Gnome session to:

printf 'Desktop: %s\nSession: %s\n' "$XDG_CURRENT_DESKTOP" "$GDMSESSION"
Desktop: ubuntu:GNOME
Session: ubuntu

After that this user did not experience the freezing problem.

I have no idea how any of this works, but I did notice, after I made a second user, that the second user was on a different gnome session and they did not experience the problem.

Invention1
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