Separate /usr now requires an initramfs - 05/01/2024 00:00 GMT

Systems which have /usr and / on separate filesystems have always required a
dedicated initramfs to bring up both partitions. Systems where both /usr and /
are on the same filesystem may use an initramfs if they wish, or choose not
to.

Historically, Gentoo has tried to make the separate filesystems use case work
anyway. Despite all our efforts, it is broken and continues to get more broken
under various configurations. The only workable solution is to support
separate /usr but only when an initramfs is present. For more details on why
this is broken, see:

- https://bugs.gentoo.org/868306#c10
- https://bugs.gentoo.org/902829
- http://freedesktop.org/wiki/Software/systemd/separate-usr-is-broken
- https://bugs.gentoo.org/915379
- https://github.com/trofi/nix-guix-gentoo/commit/43d84cc00af530ef912d9c98448b64d6b5282907
- https://github.com/trofi/nix-guix-gentoo/commit/8f194519982fbfabb6b3ca84c0806b1a379b5d06
- https://bugs.gentoo.org/825078

In 2013, Gentoo policy determined that separate /usr without an initramfs was
officially no longer supported:

- https://projects.gentoo.org/qa/policy-guide/filesystem.html#pg0202
- https://gitweb.gentoo.org/data/gentoo-news.git/tree/2013/2013-09-27-initramfs-required/2013-09-27-initramfs-required.en.txt?id=a79dd69b0cca439bc0c483c9193c79e0554819d0

11 years later, the support is being withdrawn. On 2024-02-05, we plan to
begin work on decommissioning existing workarounds and will not accept any
more.

User Action Required
====================

If you have separate /usr and are not currently using an initramfs, you have
until 2024-02-05 to set up an initramfs. If you do not, then at some point on
or after this date, routine system upgrades will leave your system unbootable.

For details on setting up an initramfs, see:

https://wiki.gentoo.org/wiki/Initramfs/Guide