Ubuntu – Mostly unable to boot when [ ***] A start job is running for… FOREVER!


A mostly clean install of Ubuntu 20.04 occasionally boots quickly and flawlessly, but almost always hangs during boot. Sometimes it will boot 1 out of 3 times, other times I reboot 10+ times, spending 30 minutes or more just watching the boot hang, then eventually holding down the power button to force shutdown and try to boot again. 

The issues usually (but not always) start just after the line [OK] started load/save RF kill switch status . That line is followed by a series of [ ***] A start job is running for... followed by all kinds of things, including installed software or /dev/disk/by-uuid pointing to both the EFI partition and the /home partition. 

These run for awhile, sometimes changing to [FAILED], [DEPEND], or [TIME] and some [OK]s afterwards as well. Then there are blocks that end in rcu_sched self-detected stall on CPU... lines. 
Basically, once I see those red [  *** ] A start job... things happening, it doesn't ever finish booting after that. I've sometimes let it try for 15 minutes or more. 

Boot messages

Similar sounding issues and things I've tried:  

People often pointed to nomodeset or nouveau.modeset=0 in GRUB. Mine is currently set with: nosplash nomodeset nouveau.modeset=0 and it boots sometimes, but mostly not. When I added noacpi noapic irqpoll as suggested, it would also sometimes boot, but with no touchpad or pen touch support, only the touchscreen (with a finger). Removing those options doesn't seem to have hurt anything and made my touchpad and pen work again — at least, when it boots.

The solutions to posts like these usually point to the swap uuid being misidentified in fstab, but my blkid and fstab entries all match. Following other forum advice about swap on SSDs, I've also set noswap, commented out the swap partition in fstab, and then deleted the swap partition entirely since I have an SSD and 16 GB RAM — though I'm open to advice if this isn't a good choice!

My Hardware:
I've installed Ubuntu in UEFI mode in a dual-boot with Windows 10 on a Samsung Notebook 9 Pro np940x5n:

  • Processor: 8th Generation Intel Quad-Core i7-8550U
  • Memory: 16GB, 2133MHz DDR4
  • Hard drive size: 256 GB SSD
  • Video: AMD Radeon 540 graphics driven by 2GB GDDR5 dedicated video memory

I'm not sure how to provide any relevant logs of the failed boots, but I hope someone can help. This is my everyday & work computer and I'm really stuck without being able to rely on it. Many thanks in advance if you have any ideas!

Best Answer

The problem relates to EFI.

Here is an incomplete solution, but enough that I can debug further. I can get it to boot by blacklist EFI modules and disabling ACPI. That is, I need this:

module_blacklist=efi_rts_wq,efi_call_rts acpi=off

I found these hints at CPU soft lockup on Samsung Notebook 9 Pro | Reddit.

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