How to remove Linux from my Mac? I have installed Ubuntu on my Mac. But then after a few times, neither can I boot to Ubuntu nor can I find where it actually is. Total a mystery. Now I actually try to erase this part in my computer. But I don't know where to start. Even in Disk Utility I do not see the space it takes. Here is a screenshot:



Please advise me how to erase Ubuntu and release the space. My internal SSD has a total size of 251 GB. But now I can only see 165 GB of it. 

Thank PSN for his advice.But something weird just happened again.. This is what happened in my terminal when I tried to install the rEFInd: 

dhcp-10-176-3-41:~ anthony$ /Users/anthony/Downloads/refind-bin-0.10.0/refind-install 
Not running as root; attempting to elevate privileges via sudo....
ShimSource is none
Installing rEFInd on OS X....
Installing rEFInd to the partition mounted at /Volumes/ESP
Found rEFInd installation in /Volumes/ESP/EFI/refind; upgrading it.

**** ALERT: SIP ENABLED! ****

You are attempting to upgrade an existing installation, but it appears that
System Integrity Protection (SIP) is enabled. If rEFInd is working now, then
this is fine; you can upgrade your existing rEFInd. If rEFInd is not working,
though, re-installing from this boot will not help. To re-enable rEFInd, you
must re-install it from a Recovery system or from another OS. To enter the
Recovery system and re-install rEFInd:


Reboot
Hold down Command+R as the chime sounds
When the OS has booted, select Utilities->Terminal
Change to this directory with the 'cd' command; it will probably be under
 /Volumes/Macintosch/Users/anthony
Re-run this script.


For more on this subject, see http://www.rodsbooks.com/refind/sip.html

Do you want to attempt installation (Y/N)? y
Copied rEFInd binary files

Notice: Backed up existing icons directory as icons-backup.
Existing refind.conf file found; copying sample file as refind.conf-sample
to avoid overwriting your customizations.

Could not set boot device property: 0xe00002bc

WARNING: If you have an Advanced Format disk, DO NOT attempt to check the
bless status with 'bless --info', since this is known to cause disk corruption
on some systems!!

ALERT:
Installation has completed, but problems were detected. Review the output for
error messages and take corrective measures as necessary. You may need to
re-run this script or install manually before rEFInd will work.

Unmounting install dir
Volume EFI on disk0s1 unmounted
I think the easier solution for you is : 

• Do a back of your Macintosh partition : (Use Time Machine is probably a good idea)

• Restart you're computer with alt R (Recovery mode)
 (You may need to be connected to internet with an ethernet connexion)

• From there Do a clean install within your time machine.



And there you should be done !