For the past couple of months my office desktop occasionally freezes. Occasionally.
On the computer I am using Slackware 64-bit 14.2 with the latest supported kernel 4.4.190. The hardware includes an Asus Z170 main board with the latest BIOS, a quad-core Intel Core Sylake i5-6400, Intel integrated graphics using the i915 module, 16 GB RAM, and two spinning hard drives.
This is not a system freeze. I can toggle to alternate consoles and SSH into the system. Methodically trying to stop processes has proven futile. The desktop is just plain frozen. Typically I resort to the wonderful
Initially I thought the problem might be the MATE desktop. I switched to Xfce. After the switch all was calm for about 10 days. Then I discovered I was unable to VNC into the desktop from my laptop. Walking to the office I found the desktop frozen.
While the recent freeze is only one Xfce data point, I am willing to concede that MATE probably was not the cause of the previous freezes.
The freeze always occurs when I am away from the desktop. This seems to imply screen savers, but MATE and Xfce use different screen savers. When I was using MATE I had disabled the screen saver. I now have done likewise with Xfce, which uses xscreensaver.
Firefox, Thunderbird, X11VNC, and VirtualBox are always running. One possible clue is with the two most recent freezes, Thunderbird was in the middle of sending alerts. For the alerts I was using the Mailbox Alert addon. On a hunch I disabled the addon. Only time will tell if that was the trigger.
Debugging intermittent issues is always a challenge. Hopefully I resolve this irritant.