Ubuntu 18.04 crashes on resuming from suspend
I have experienced the same issue with an HP Pavilion 11 x360.
The kern.log suggests that it thinks it has gone into suspend - PM: suspend entry (deep) - but the system seizes up at that point and there are then no further entries until you shutdown and reboot.
A 'successful suspend' would have futher entries PM: Syncing filesystems ... done., Freezing user space processes... etc
The screen goes blank but the power LED stays on (as does the fan if it is already running) and a hard reset (holding down the power button) is required to be able use the machine again.
Even using an 18.04 live USB results in the same suspend problem, which suggests it isn't because of any additonal programs I have installed.
Three other different laptops (friend's and my own) have no issues with suspend on 18.04, leading me to wonder what specific hardware combination causes this to occur.
All the laptops (including the 'problem child') have intel graphics.
The 'problem laptop' suspends fine with Ubuntu 17.10, Kubuntu 17.10, Devuan Jessie, Devuan ASCII and Windows 10 but fails to suspend with Ubuntu 18.04 and Kubuntu 18.04.
(Initially the suspend problem also occured when trying to use kernels 4.15, 4.16 and 4.17, but the more recent 4.17 and 4.18 kernels have an update that has allowed suspend to work again on this machine)
Using UKUU to install the most recent 4.14 kernel (4.14.47) on 18.04 fixed the problem. (The accepted answer by Matalak) - would now recommend trying a recent 4.17 or 4.18 kernel.
Edit - Please take a look at the steps here to see if any other fixes might resolve your issue first: Ubuntu 18.04 - Dell XPS13 9370 no longer suspends on lid close
I had trouble finding a bug report about suspend causing a completely unresponsive system on 18.04, which suggested that it was not affecting a large proportion of users.
Although it's good that it wasn't affecting a vast number of users, it can make it more difficult to find out where the issue lies if only a handful of people are experiencing problems with their specific hardware setup.
Edit - A bug report has been opened, the likely culprit appears to have been identified and a patched version of the 4.15 kernel was put together to resolve the suspend issue - the patch is now in the more recent 4.17 and 4.18 kernels https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1774950
Further Edit - As of 11th September 2018 the standard system update kernel (4.15.0-34) now has the patch, which has been backported by those kindly developers and suspend works again as it should on the problem laptop with the Intel N3540. Much praise to their work!
Just to be clear though, it's an issue with trying to suspend your machine on 18.04 where the screen goes blank (but it clearly hasn't gone into 'suspend') and then doesn't react to anything else except holding down the power button to shut it down.
I solved the problem by installing UKUU and downgrading to kernel 4.14.41. Perhaps there is an incompatibility with the hardware in later kernel versions.
I believe it is the buggy nouveau driver. Try adding:
nouveau.modeset=0
to GRUB_CMDLINE_LINUX in the /etc/default/grub file, after that run:
sudo update-grub
sudo reboot
And voila no more hangs on resume from suspend.