If you violate probation with 6 months left out of 5 yrs... do you have to serve the 5 yrs. Or just what is left... thanks

You will find out this answer at your probation violation hearing. At that time the Judge will decide what sentence you will get for your violation. It could be the entire 5 years in jail or it could be some time in jail and more probation or it could be more probation. It's all up to the Judge to decide. And no, you don't just "do" the remaining 6 months that are left.