Comment 28 for bug 1829402

Thanks for testing, Jackneill.

To explain, the "dis_ucode_ldr" option disables loading of microcode updates by Linux. Microcode updates are are binary blobs (no source code is available) which modify operation of a CPU until the next reboot. They are supplied by CPU manufacturers / vendors to mainboard manufacturers / vendors and are now more commonly shared with operating systems, too. Linux supports loading them into the CPU during early boot.

Unfortunately, with the latest microcode update (which was released by the same time as the kernel updates you reported about on 19.04 and 18.04 LTS), your CPU seems to not behave reliably, causing a high percentage of your boots into Ubuntu to fail. This root cause is confirmed by using the dis_ucode_ldr kernel boot parameter, which, as you report, ensures your system boots up fine every time.

I will now mark this bug report as a duplicate of bug #1829620 (I am convinced both Kai-Heng and TJ meant to point to the same bug report) and suggest you keep using "dis_ucode_ldr" temporarily until Intel releases a new microcode update and it becomes available in Ubuntu via https://packages.ubuntu.com/search?keywords=intel-microcode - the status of bug #1829620 should change to "fix released" at that time. Feel free to address me on IRC (#ubuntu) in case of any questions of a support nature, or add to the bug report if you would like to report more details on this issue.