What is the eligibility criteria to appear for IAS exam?

CBI recruits candidates through direct recruitment, deputation, promotion by seniority or through Limited Departmental Competitive Examination. All direct recruitment of Group C posts for sub-inspectors, constables and lower division clerk are made through Staff Selection Commission (SSC). Procedure

The eligibility criteria, syllabus and other details for IAS exam is clearly described in this link. You can refer it: https://www.iassolution.com/ias-exam-pattern-eligibility-syllabus/