amd64 17.1 profiles are now stable
A new set of 17.1 amd64 profiles has been added to the Gentoo repository in Dec 2017. These profiles switch to a more standard 'no SYMLINK_LIB' multilib layout, and require explicit migration as described below. They are considered stable at the moment, and we would like to request all users to upgrade their systems. The old profiles will be deprecated in the near future.
In the new profiles, the lib->lib64 compatibility symlink is removed. 64-bit libraries need to be installed directly to lib64. /lib and /usr/lib become real directories, that are used for cross-arch and native non-library packages (gcc, clang) and 32-bit libraries on the multilib profile (which improves compatibility with prebuilt x86 packages).
Migration from both 13.0 and 17.0 profiles is supported. In case of the former, reading the news item for 17.0 upgrade  is recommended.
The migration is performed using app-portage/unsymlink-lib tool. The following steps can be used to upgrade your system:
1. Sync and upgrade your system to the newest package versions to reduce the risk of issues.
2. If you are still running a 13.0 profile, select gcc 6.4.0 or later as the system compiler, source /etc/profile and reinstall libtool:
# gcc-config -l  x86_64-pc-linux-gnu-5.5.0 *  x86_64-pc-linux-gnu-8.3.0 # gcc-config 2 # . /etc/profile # emerge -1v libtool
3. Install the tool:
# emerge -1v app-portage/unsymlink-lib
4. Run 'unsymlink-lib --analyze' and check the output for obvious mistakes. If you need to perform any changes to the system, remember to run 'unsymlink-lib --analyze' again afterwards.
[past this point do not call emerge or modify /usr manually]
5. This is a very good time to make a backup.
6. Run 'unsymlink-lib --migrate'. You can add '--pretend' first to see what is going to happen.
7. Reboot your system. Check if important programs work. In particular, verify that e.g. 'emerge --info' works (but do not install anything). If you hit any serious problems, you can use 'unsymlink-lib --rollback' to revert the changes and return to step 4.
8. Run 'unsymlink-lib --finish'. You can add '--pretend' first to see what is going to happen but note that you're going to see a very long list of files to remove.
9. Switch the profile, e.g.:
# eselect profile set default/linux/amd64/17.1/desktop
[at this point you can start using emerge again]
10. Rebuild the toolchain:
# emerge -1v sys-devel/gcc:8.3.0 [ repeat for other slots you will be using ] [ if you are upgrading from 13.0 profile, also: ] # emerge -1v sys-devel/binutils # emerge -1v sys-libs/glibc
11. If you are using a multilib profile, rebuild all 32-bit packages. This can be done using:
# emerge -1v --deep /lib32 /usr/lib32 /usr/lib/llvm/*/lib32
Alternatively, if you are switching from one of the 13.0 profiles you can rebuild all packages as detailed in the 17.0 news item:
# emerge -ev @world
12. Once the last 32-bit package is rebuilt, your package manager should remove the orphaned /lib32 and /usr/lib32 symlinks. If that does not happen, remove them manually:
# rm /lib32 /usr/lib32
For known issues, please see bug #506276 . If you have any problems with the new profiles or the migration procedure, please report a bug and make it block the tracker.
For more information on the layout, please see the wiki article on AMD64 multilib layouts .