Backup /Users/ directory (with tar) and make a list of useful installed /Applications/.
Download El Capitan from App Store.
Format at least 8 GB usb drive to OS X Extended file system and create install media:
cd "/Applications/Install OS X El Capitan.app/Contents/Resources" ./createinstallmedia --volume /Volumes/new --applicationpath "/Applications/Install OS X El Capitan.app"
Optionally create a slim DMG from that install media:
cd "/Volumes/Install OS X El Capitan" rm -R .Trashes/ hdiutil create -nospotlight -srcfolder "/Volumes/Install OS X El Capitan" -format UDBZ /Users/swegen/Desktop/ElCapitan.dmg
Download latest Ubuntu ISO and dd it to another at least 2 GB usb drive.
Boot to Ubuntu with option key pressed at boot. Put device to sleep by closing the lid and wake it up to unfreeze the SSD.
Open terminal and gain root rights with:
sudo passwd su
Restore SSD memory cells to factory condition with ATA secure erase command (takes about six seconds):
hdparm -I /dev/sda hdparm --user-master u --security-set-pass Eins /dev/sda time hdparm --user-master u --security-erase-enhanced Eins /dev/sda
Optionally clear SMC and NVRAM to start install afresh.
Boot with El Capitan usb install media and start terminal to create 1MB aligned OS partition while preserving default EFI partition starting location and size to allow for future firmware updates (sizes are calculated for 250 GB SSD):
gpt create /dev/disk0 gpt add -b40 -s409600 -tefi /dev/disk0 gpt label -i1 -l "EFI System Partition" /dev/disk0 gpt add -b411648 -s488552448 -thfs /dev/disk0 gpt label -i2 -lSSD /dev/disk0 newfs_hfs -s -J -v SSD /dev/disk0s2 diskutil mount /dev/disk0s2 cd /Volumes/SSD rm -R .Trashes/
Exit terminal and install El Capitan.
Installer replaces basic OS partition with unnecessary Core Storage volume manager. After installation is complete Remove Core Storage layer from GPT:
diskutil cs list diskutil cs revert %lvuid%
Reboot and check again with above list command that it worked. Then restore your backups. Final partition layout (efi, hfs and recovery) is:
# gpt show /dev/disk0 start size index contents 0 1 PMBR 1 1 Pri GPT header 2 32 Pri GPT table 34 6 40 409600 1 GPT part - C12A7328-F81F-11D2-BA4B-00A0C93EC93B 409640 2008 411648 488552448 2 GPT part - 48465300-0000-11AA-AA11-00306543ECAC 488964096 1269536 3 GPT part - 426F6F74-0000-11AA-AA11-00306543ECAC 490233632 1087 490234719 32 Sec GPT table 490234751 1 Sec GPT header
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