I've just bought a new Macbook Air (running Yosemite) and I am trying to create a partition from my Macintosh HD SSD for dual-booting Ubuntu. However when I try to create a partition in Disk Utilities, I keep getting the error "This Core Storage operation is not allowed on a sparse logical volume group." I have tried restarting the system in Recovery Mode and verifying and repairing the disk, but it did not work. What can I do to partition? (I would prefer to not format the SSD.)
You have to boot from another device or to Internet Recovery Mode and then use the command line to modify the CoreStorage volume.
Backup your data.
Detach any external drive (especially your external Time Machine backup drive).
Restart to Internet Recovery Mode by pressing altcmdR at startup.
The prerequisites are the latest firmware update installed, either ethernet or WLAN (WPA/WPA2) and a router with DHCP activated.
On a 50 Mbps-line it takes about 4 min (presenting a small animated globe) to boot to a recovery netboot image which usually is loaded from an apple/akamai server.
I recommend ethernet because it's more reliable. If you are restricted to WIFI and the boot process fails, just restart your Mac until you succeed booting.
Alternatively you may start from a bootable installer thumb drive (Mavericks or Yosemite) or a thumb drive containing a full system (Mavericks or Yosemite).
Open in the menubar Utilities/Terminal
Enter diskutil cs list
Enter diskutil cs resizeStack LVUUID size with LVUUID: UUID of the logical volume and size: the final size of your Macintosh HD
Example: diskutil cs resizeStack DC2473AF-0833-4DBD-BF8F-D5D60063554A 200g
Enter exit and quit Terminal.
Reboot to your main volume.
Start installing Ubuntu to the now unallocated disk space.