A maximum of 6 attempts is permitted to every candidate and 9 to those belonging to Other Backward Classes. There is no restriction on the number of attempts in the case of SC/ST candidates. All this, provided you are still under the age limit.
A physically handicapped person will get as many attempts as any other non-handicapped candidate of his/her community, but if they are from the general category they will get 9 attempts.
It is wiser to be mentally ready for several attempts as cracking the Civil Services Exams is a tough nut to crack the first time around; and if you do qualify you may want to attempt again to improve your ranking and therefore your service allotment.
A candidate who is appointed to the Indian Administrative Service or the Indian Foreign Service on the results of an earlier examination and continues to be a member of that service will not be eligible to compete at this examination.
In case such a candidate is appointed to the IAS/IFS after the Preliminary Examination of Civil Services Examination, 2015 is over and he/she continues to be a member of that service, he/she shall not be eligible to appear in the Civil Services (Main) Examination, 2015 notwithstanding his/her having qualified in the Preliminary Examination, 2015.
Also provided that if such a candidate is appointed to IAS/IFS after the commencement of the Civil Services (Main) Examination, 2015 but before the result thereof and continues to be a member of that service, he/she shall not be considered for appointment to any service/post on the basis of the result of this examination viz. Civil Services Examination, 2015.