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"What are phased updates, and why does Ubuntu use them?" states that sudo apt upgrade will often display "The following packages have been kept back" when an update to a stable release is made available to only a fraction of users at first. Ubuntu does this to limit the impact of unforeseen defects in updated software. "StableReleaseUpdates section Phasing" on Ubuntu Wiki states that most packages are phased in at a rate of 10 percent of the user base per 6 hours, or the entire user base within 3 days. (The wiki page cites an article by Brian Murray via a link that has since become broken. Fortunately, Murray's article "Phasing of Stable Release Updates" is archived.)

However, a few packages appear to phase in much more slowly than that. On both of the Xubuntu 22.10 machines I run, updates to grub-efi-amd64-bin, grub-efi-amd64-signed, and shim-signed have been kept back for 20 days according to the automatically generated report "Phasing Ubuntu Stable Release Updates". This long phasing time for GRUB has led to confusion among other users, such as a question by raddevus and a question by Syn Romana.

Are the rationale and rate for slower phasing of GRUB and shim documented publicly?

Damian Yerrick
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  • It's likely not a difference of policy or rationale. Those engineers, like all us, have multiple projects, many tasks to accomplish each day, different emergencies to address, and some priorities are set by others. For example, Debian 12's Hard Freeze is later this week. If you REALLY want to know the story behind the delay, drop by https://discourse.ubuntu.com and ask. They might-or-might-not be able to disclose much, since some error report(s) might be private for several good reasons. – user535733 Mar 10 '23 at 03:03

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The source code for phased-updater lists grub2, shim, and secureboot-db in a set called SLOW_PACKAGES. These packages are phased in at 1 percent per 6-hour run rather than 10 percent. The feature was added in commit bd8ae78d47 with only secureboot-db, and grub2 and shim were added in commit e2fbf46b54, both with what appear to be one-line commit messages.

This solves the "how" of the question, leaving the "why": how packages are chosen for SLOW_PACKAGES and why the rate is as slow as the better part of a month.

Damian Yerrick
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