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.
在2023年下半年，systemd将会放弃对于split-usr/unmerged-usr系统的支持[1]。所有使用systemd的Gentoo系统需要切换到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.
切换到merged-usr会把所有/bin、/sbin和/lib目录下的文件移动到/usr/bin和/usr/lib下。这些/里的目录会被符号链接代替。

To facilitate this, a new set of sub-profiles has been created, and a script is available to perform the actual migration.
我们为此创建了一套新的子profiles和一个用于执行真正迁移任务的脚本。

To migrate a system to merged-usr, follow this procedure:
请通过以下步骤将系统迁移成merged-usr。

1. Ensure your system backups are up to date.
1. 确保你的系统备份了。

2. Install sys-apps/merge-usr.
2. 下载sys-apps/merge-usr。

3. Run the merge-usr script. The --dryrun option may be used to check for error conditions before running the script for real.
3. 运行脚本merge-usr。--dryrun选项可以用来在实际执行前检查可能的错误情况。

4. Switch to a merged-usr profile.
4. 切换到merged-usr profile。

     eg. eselect profile set default/linux/amd64/17.1/systemd/merged-usr
     比如，运行命令：eselect profile set default/linux/amd64/17.1/systemd/merged-usr

5. Run emerge with the --newuse or --changed-use option to rebuild any packages that have a "split-usr" USE flag.
5. 使用--newuse或--changed-use选项运行emerge，以重建所有具有"split-usr"这个USE标记的软件包。

     eg. emerge -uDN @world
     比如，运行命令：emerge -uDN @world

For new installs, new "mergedusr" stage3 tarballs are being produced for commonly used profiles.
对于新的下载，已为常用的profiles提供了新的stage3压缩包"mergedusr"。

[1] https://lists.freedesktop.org/archives/ … 48352.html