Hey all — So my brother deleted some files in /usr/lib, and now my iMac won't fully boot. No Time Machine backup unfortunately. Running 10.10.5. I can still access my iMac's drive by booting into Target Disk Mode and viewing its contents with my Macbook. All of my files still seem to be intact, so I can save all important docs with no issue. I've tried copying the contents of my Macbook's /usr/lib folder (also running 10.10.5) and I've tried copying the /usr/lib folder's contents from the Yosemite Installer (using Pacifist), but to no avail. I've also tried repairing disk permissions after copying, and still no luck. It seems the best thing to do would be to simply re-install Yosemite, but when I boot into Recovery Mode, I am only given the option to install El Capitan. I cannot do this as several critical apps for my work do not support 10.11. I've been looking into creating a bootable install drive, and it looks like I could simply do this with the Yosemite Installer and a USB key. However, since Recovery Mode only allows for 10.11, the only other option I know of is booting into the Startup Manager to select the install drive. I'm a little worried, though — would doing this erase my data, or would it simply re-install OS X and keep all of my files intact? Thanks!!