It has locked up again overnight but I can still SSH in. One possible thought is - could it be systemd-timesync which is the problem and not actually xorg?
The Xorg.0.log shows nothing unusual but syslog and kern.log are full of entries about CPU lockup, and "top" as always shows systemd-timesync as the process hogging the CPU (xorg sometimes shows up hogging 100% of CPU time in the "top" list, but systems-timesync ALWAYS does when I experience a freeze: top - 07:41:20 up 13:26, 2 users, load average: 10.00, 10.01, 9.98 Tasks: 262 total, 7 running, 252 sleeping, 0 stopped, 3 zombie %Cpu(s): 0.0 us, 14.3 sy, 0.0 ni, 85.7 id, 0.0 wa, 0.0 hi, 0.0 si, 0.0 st KiB Mem : 64276444 total, 46083912 free, 1240520 used, 16952012 buff/cache KiB Swap: 65379324 total, 65379324 free, 0 used. 62810940 avail Mem PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND 521 systemd+ 20 0 102384 2588 2352 R 100.0 0.0 727:17.66 systemd-timesyn 1 root 20 0 119860 6044 4008 D 0.0 0.0 0:01.07 systemd 2 root 20 0 0 0 0 S 0.0 0.0 0:00.00 kthreadd 3 root 20 0 0 0 0 S 0.0 0.0 0:00.01 ksoftirqd/0 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1587730 Title: graphic system freezes after a while, can still ssh into machine To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/xorg/+bug/1587730/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs