Ubuntu 18.04.2 boot stuck on purple screen after updates

Summary of Issue

Last Friday, I installed updates to Ubuntu 18.04 with sudo apt-get update && sudo apt-get upgrade. Some of these updates required a restart. Upon restart, after GRUB, boot got stuck on a purple screen before the Ubuntu logo/login. I can't access the terminal at this step through Ctrl + Alt + F7/T/F1/F2 methods. Recovery mode does not work, and gets stuck at Loading initial ramdisk...

Attempts to Resolve

As stated above, recovery mode did not work.

Attempted to use Boot Repair, this ran successfully but did not resolve the problem. Output from this attempt here.
Next, I backed up some files then attempted a fresh install of 18.04.2. This worked, but as soon as I grabbed the ~400 MB of updates for this clean install, I encountered the same problem as before. I tried using both the Software Updater, and terminal. I've got no idea what update is breaking, here's a full log of updates run.
Saw what may be a related issue here: Ubuntu freeze on boot purple screen. Seeing that this user seemed to have an issue with kernel updates, I excluded kernel updates from running and tried again, still the same result as before.

So at this point, I'm at a loss as to how to proceed. I'm hoping I can get some help on this thread. Otherwise, I may need to downgrade to 16.04 or upgrade to 19.04.

EDIT 1

Looks like this bug's already been reported to Canonical. Appears that it could be related to recent Intel microcode updates or an acpi issue.

This report cites this thread as verification multiple users are experiencing this issue, so keep chiming in if you're affected by it!
ACPI cited as a possible cause in this report
Intel microcode updates causing boot problems from some ASUS users

EDIT 2

Intel microcode updates on ASUS causing kernel to get stuck has been identified as the crux of the issue. Confirmed temporary workaround to get machines bootable is in the accepted answer below.

A video from YouTube regarding this problem and the documented workaround.

EDIT 3

As of 09/03/2019, I've installed the most recent BIOS update from ASUS (from within Windows 10) and can confirm that this enables me to boot normally into Ubuntu without the need for the dis_ucode_ldr option in GRUB. I would recommend this as a more sustainable, definitive fix for the problem than using the workaround at this point.

Solution 1:

Well I also have a Asus ZenBook UX433FA doing this issue, I was running 18.10 and did apt-get upgrade last night and broke the system.

I've since used this method livecd recovery to upgrade to 19.04 still no luck with booting. Have multiple kernels installed none of which will get past the "loading initial ramdisk". While using the above i installed kernel v5.1 with ukuu no luck either and threw errors about dkms for nvidia driver incompatible with kernel version.

Edit DMESG log

Managed to get the dmesg from a partial boot here

boot-repair log info here occasionally it will boot with errors, unsure of what info or how to gather info on these occasions though to help with debug.

Just a side note windows hadn't been loaded for about a month prior to this. I know this should probably be a comment but I don't have enough credit.

Edit 2

For anyone having a similar problem, try booting with microcode updates off: add dis_ucode_ldr to the kernel command line (from GRUB if you cannot boot) can confirm this allows for boot.

Solution 2:

I had the same issue on a brand new Asus Vivobook s15 S530FA (intel i5-8265U). After installing the first updates in ubuntu 18.04.2 LTS the boot screen got stuck in "loading initial ramdisk".

As mentioned in the above comments a workaround to this is disabling the microcode in the grub options adding: dis_ucode_ldr. This solution works for debugging this issue but it's not recommended for regular use.

The best solution so far I think is to downgrade the intel-microcode package to the previous version:

sudo apt-get install intel-microcode=3.20180312.0~ubuntu18.04.1

Then freeze the package to avoid accidental upgrade:

sudo su 
echo "intel-microcode" hold | dpkg --set-selections

For now I'll avoid installing intel-microcode=3.20190514.0ubuntu0.18.04.3

Solution 3:

I found a durable solution in the bug tracker, see WORKAROUND 3: upgrade BIOS.

ASUS released a BIOS update for the UX433FN the 2019.06.17 (please check your exact model: sudo dmidecode -t system, sudo dmidecode -t bios for BIOS version).

WARNING: Updating BIOS is a risked operation and can not be reverted !!

Overview: You basically have to download a zip, extract the file it a USB key, go into BIOS and start Flash Utility, select the file and that's it (you can do it from Ubuntu).

Here are the detailed steps:

Go to asus drivers download page (for me was this)
Download BIOS file (UX433FNAS306.zip)
Extract the file from zip archive to your USB key -> UX433FNAS.306 (my advice: remove the zip file for ensure you will not confund the files after)
Reboot and go to setup (BIOS), navigate to Advanced > Start Easy Flash
In the scary blue program navigate to select the file UX433FNAS.306 (NOT the zip !!!)
Press enter and confirm (it could freeze for 1 minute but it works)
(If you edited your grub now you can set it back to normal)

Solution 4:

Having exactly the same issue on a brand new Asus ZenBook UX433FA. Installed Ubuntu 18.04.02 with dual boot, started up without problem, but after installing the first batch of upgrades and rebooting I got the same purple screen.

I found a temporary fix by disabling Secure Boot (booting with nomodeset, then command line sudo mokutil --disable-validation). Works fine after that, so I suspect it has something to do with with some driver(s) included among the updates. Any suggestion how to fix this more permanently?