After patching a regression that caused boot failures on some AMD machines in Ubuntu 14.04 LTS, and then releasing a Linux kernel security update for Ubuntu 18.04 LTS users (which addressed a total of six security vulnerabilities, one of which was also causing boot failures due to regression on both AMD and Intel machines), Canonical has now released another kernel fix that should altogether fix regressions causing boot failures on 64-bit machines, as well as for OEM processors, systems running Amazon Web Services, Microsoft Azure, Google Cloud Platform, and other cloud environments.
The security advisory put out by Canonical sums it up:
“USN-3695-1 fixed vulnerabilities in the Linux kernel for Ubuntu 18.04 LTS. Unfortunately, the fix for CVE-2018-1108 introduced a regression where insufficient early entropy prevented services from starting, leading in some situations to a failure to boot, this update addresses the issue. We apologize for the inconvenience.”
The patch is also available for users on Ubuntu 16.04.4 LTS with the HWE kernel. Canonical allows users of previous Ubuntu LTS (Long Term Support) versions to use the newer Linux kernel of later Ubuntu LTS versions. So if you’re on Ubuntu 16.04.4 LTS with the HWE kernel from Ubuntu 18.04 LTS, this patch applies to you as well.
It is highly recommended that Ubuntu 18.04 LTS and Ubuntu 16.04 LTS users update their installations to the latest Linux kernel versions available from the main software repos. Ubuntu 18.04 LTS users should update to linux-image 4.15.0-29.31, while Ubuntu 16.04.4 LTS users should update to linux-image 4.15.0-29.31~16.04.1.