Surely if your Mac has more than one operating system installed in the form of dual boot or through Boot Camp, you may want to share your library of iTunes on both systems If your Mac has multiple partitions run different operating systems with one dual boot On OS X, you may decide that you want to share the exact same iTunes library across different operating systems.
With this we manage not to have songs or any other type of duplicate content on the disk since it will not matter what system we are running at that moment since the information will not be duplicated and will therefore occupy more space.
There is a little-known way to force iTunes to rebuild or redo select a library and the truth that works perfectly to share libraries across disk partitions. Let's see the steps to take:
First we will boot the partition that we want to have access to the iTunes library, that is, the partition where the primary iTunes library is not located, for example, »Yosemite HD«. Now we will run iTunes with the ALT key pressed, at that time we will choose the iTunes library. Now as simple as going to the path where we have our library on the primary partition / Macintosh HD / Users / Miguel / Music / iTunes and selecting the iTunes library to complete the process.
Now iTunes will take a little time to select the new iTunes Library location, where it will begin to place and organize all the content, songs, music and files from the other partition and thus we will have the exact library on both partitions. This works especially well for managing large iTunes collections on smaller hard drives that don't have enough space, as the entire media library can be downloaded in one USB drive or external hard drive, and still have all the contents accessible from your Mac or PC with iTunes.