Ubuntu – Change shutdown confirmation timer

Editing /etc/default/grub:

GRUB_CMDLINE_LINUX_DEFAULT="quiet splash acpi=off"

and executing:

sudo update-grub

is known to eliminate these ACPI warnings in many cases. See https://unix.stackexchange.com/questions/97974/how-do-i-remove-acpi-warning-on-boot

However the ACPI Warnings are usually considered harmless. These might not be the cause of your hung shutdown.

BIOS reset:

Warning: resetting your motherboard configuration is an option of last resort - it may solve your problem, it may leave your system un-bootable! If your motherboard supports making a backup of your configuration, by all means do it before proceeding.

There are two methods of resetting the motherboard config and, in my experience, they can leave the motherboard with two different configurations

Built-in Factory Reset/Default: This will load into non-volatile memory a configuration the manufacturer figures will run, without modification, in the majority of circumstances. However, it does not necessarily zero out NVM which might leave you with bad data somewhere in CMOS.

CMOS zeroing: This method involves removing power from the motherboards non-volatile memory (historically CMOS) to zero it out. It will leave a default configuration but not necessarily the same one achieved above.

Procedure:

1. Remove power from your system. (pull the plug!)
2. Ground yourself to chassis to prevent static discharge damage.
3. Open chassis
4. Remove battery (CR2032 typically)
5. Short out the battery contacts with a paper clip for 5 seconds.
6. Replace battery (with new if there is any doubt...)
7. Close chassis
8. Apply power

IMPORTANT: CMOS memory can run on very little current. You must short out the battery contacts to discharge any residual charge or you will not zero CMOS memory effectively!

Typically, I will (testing between each attempt) Factory Reset, Zero CMOS, Factory Reset one last time. If the problem still exists, I look elsewhere.