Create El Capitan install partition I went through a lot of articles on how to create bootable os x install partition but eventually I ended up with a need of making resize of my system partition - unfortunately DiskUtility shows this option greyed out. Any ideas why? I don't want to loose my existing system installation.



Properties say that it is a physical volume and it's not using CoreStorage.
This is the output of diskutil list command:



And it seems like I managed to resize this disk0s2 partition with:

diskutil resizeVolume disk0s2 480GB


command. Still don't get why this option is absent in DiskUtility. It used to be there. And unfortunately this is not what I was looking for. After I resized this volume DiskUtility didn't allow me to create a new partition. Therefore I think the problem is in that I didn't partition drive properly from the very beginning. diskutil splitPartition doesn't work at all - it says that it cannot unmount disk. Any ideas other than to wipe HDD contents out and install from scratch? I don't want to install Snow Leopard first and update it to El Capitan.
Try to return everything back:

diskutil resizevolume disk0s2 R


and then:

diskutil resizeVolume disk0s2 480G jhfsx InstallOSX 10G



  Resizing a volume that is currently set as the computer’s startup disk
  will invalidate that setting; use the Startup Disk System
  Preferences panel or bless (8) to reset the resized volume as the
  startup disk.