Ubuntu 18.04 LTS hangs up every time with AMD GPU
June 14, 2018 Update
Based on this ArchLinux forum thread it appears you need to add:
amdgpu.dc=0
to your /etc/default/grub LINUX line after quiet splash. Then run sudo update-grub.
Being a new install of Ubuntu 18.04 you are one of the lucky ones that can use journalctl to look at the last boot (which locked up). Use:
journalctl -b-1
Then press the End key to jump to EOF (End Of File). In my successful last boot it says:
Jun 10 16:18:51 alien systemd[1]: Unmounting /mnt/d...
Jun 10 16:18:51 alien systemd[1]: Unmounted /run/user/1000.
Jun 10 16:18:51 alien systemd[1]: Unmounted /media/rick/Ubuntu 18.04 LTS amd64.
Jun 10 16:18:51 alien systemd[1]: Unmounted /boot/efi.
Jun 10 16:18:51 alien ntfs-3g[648]: Unmounting /dev/nvme0n1p8 (Shared_WSL+Linux)
Jun 10 16:18:51 alien ntfs-3g[648]: Permissions cache : 21 writes, 4033288 reads, 99.9% hits
Jun 10 16:18:51 alien systemd[1]: Unmounted /media/rick/casper-rw.
Jun 10 16:18:51 alien systemd[1]: Unmounted /mnt/e.
Jun 10 16:18:51 alien ntfs-3g[736]: Unmounting /dev/sda3 (HGST_Win10)
Jun 10 16:18:51 alien ntfs-3g[736]: Permissions cache : 754 writes, 4108560 reads, 99.9% hits
Jun 10 16:18:51 alien ntfs-3g[637]: Unmounting /dev/nvme0n1p4 (NVMe_Win10)
Jun 10 16:18:51 alien ntfs-3g[637]: Permissions cache : 987 writes, 4983239 reads, 99.9% hits
Jun 10 16:18:51 alien systemd[1]: Unmounted /mnt/d.
Jun 10 16:18:51 alien systemd[1]: Unmounted /mnt/c.
Jun 10 16:18:51 alien systemd[1]: Reached target Unmount All Filesystems.
Jun 10 16:18:51 alien systemd[1]: Stopped target Local File Systems (Pre).
Jun 10 16:18:51 alien systemd[1]: Stopped Remount Root and Kernel File Systems.
Jun 10 16:18:51 alien systemd[1]: Stopped Create Static Device Nodes in /dev.
Jun 10 16:18:51 alien systemd[1]: Reached target Shutdown.
Jun 10 16:18:51 alien systemd[1]: Reached target Final Step.
Jun 10 16:18:51 alien systemd[1]: dev-disk-by\x2dpartlabel-Basic\x5cx20data\x5cx20partition.device: Dev dev-
Jun 10 16:18:51 alien systemd[1]: Received SIGRTMIN+20 from PID 18665 (plymouthd).
Jun 10 16:18:51 alien systemd[1]: Started Show Plymouth Reboot Screen.
Jun 10 16:18:51 alien systemd[1]: Starting Reboot...
Jun 10 16:18:51 alien systemd[1]: Shutting down.
Jun 10 16:18:51 alien kernel: systemd-shutdow: 36 output lines suppressed due to ratelimiting
Jun 10 16:18:51 alien systemd-shutdown[1]: Sending SIGTERM to remaining processes...
Jun 10 16:18:51 alien dnsmasq[1393]: exiting on receipt of SIGTERM
Jun 10 16:18:51 alien systemd-journald[288]: Journal stopped
lines 46804-46832/46832 (END)
In yours you need to look for error messages.
You may have to use the Page Up key to see them.
When you have found what you are looking for (or have given up looking) press Q to exit.
If overheating was causing the shutdown you can install Intel Powerclamp: Stop cpu from overheating
Besides lm-sensors you can get temperature readings for all thermal zones directly from the command line using this one-liner:
$ paste <(cat /sys/class/thermal/thermal_zone*/type) <(cat /sys/class/thermal/thermal_zone*/temp) | column -s $'\t' -t | sed 's/\(.\)..$/.\1°C/'
INT3400 Thermal 20.0°C
SEN1 44.0°C
SEN2 52.0°C
SEN3 64.0°C
SEN4 59.0°C
B0D4 73.0°C
pch_skylake 76.5°C
x86_pkg_temp 73.0°C
Reported in Celsius and drop the last three zeros.