"/usr merge" is the process of making /bin, /sbin, and /lib to be symlinks
to corresponding directories in /usr. It is done in Fedora and several
other distros now, and also in Solaris 15 years ago.
Benefits from /usr merge are described here:
http://www.freedesktop.org/wiki/Software/systemd/TheCaseForTheUsrMerge/
Technical details are here:
http://aababilov.wordpress.com/2013/07/17/usr-merge-in-gentoo/

In few words, the script is run once to merge /usr on a running system.
Also, the script is installed in post_src_install hook to perform /usr
merge during package updates or installations.

2013/8/13 ¶«·½ÙãÀ× <dongfangxunlei@gmail.com>

> more information?
>
>
> 2013/8/13 Alessio Ababilov <ilovegnulinux@gmail.com>
>
>> Hi!
>>
>> I wrote a script that allows /usr merge in Gentoo without changes to
>> ebuilds.
>>
>> I described it in an article
>> http://aababilov.wordpress.com/2013/07/17/usr-merge-in-gentoo/
>>
>> Are there any volunteers to test it? I use it on my computers for two
>> months.
>>
>> Alessio Ababilov
>> Senior Software Engineer
>> Grid Dynamics
>>
>
>