/usr merge for systemd users

Title: /usr merge for systemd users
Author: Mike Gilbert <floppym@gentoo.org>
Posted: 2022-12-01
Revision: 3
News-Item-Format: 2.0
Display-If-Installed: sys-apps/systemd

In the latter half of 2023, systemd will drop support for
split-usr/unmerged-usr systems [1]. All Gentoo systems running systemd
will need to be migrated to merged-usr.

Migrating to merged-usr will move all data from /bin, /sbin, and /lib
into the /usr/bin and /usr/lib directories. The directories in / are
replaced with symlinks.

To facilitate this, a new set of sub-profiles has been created, and a
script is available to perform the actual migration.

To migrate a system to merged-usr, follow this procedure:

1. Ensure your system backups are up to date.

2. Install sys-apps/merge-usr.

3. Run "merge-usr --dryrun" as root to check for conflicts. These will
   appear with the word ERROR at the start of the line.

4. Resolve any conflicts. This may involve deleting duplicate files. If
   in doubt, seek support in a Gentoo support channel.

5. Run the merge-usr script from a root shell. Avoid running it via sudo
   directly to avoid locking yourself out if an unexpected error occurs.

6. Switch to a merged-usr profile.
     eg. eselect profile set default/linux/amd64/17.1/systemd/merged-usr

7. Run emerge with the --newuse or --changed-use option to rebuild
   any packages that have a "split-usr" USE flag.
     eg. emerge -uDN @world

For new installs, new "mergedusr" stage3 tarballs are being produced for
commonly used profiles.

[1] https://lists.freedesktop.org/archives/systemd-devel/2022-September/048352.html