Whenever the office of the President falls vacant either due to death or resignation or impeachment, the Vice-President officiates for a period not more than six months.
The Constitution has made it obligatory that in such cases (of vacancy in the office of President) election for a new President must be held within six months.
The newly elected President then holds office for his full term of five years.
Thus, when President Fakhruddin Ali Ahmad died in 1977, Vice-President B. D. Jatti officiated and the new President (Sanjeeva Reddy) was elected within six months.
In case the President’s office falls vacant and the Vice-President is not available (or Vice- President acting as President dies or resigns in less than six months), the Chief Justice (or if his office is also vacant, the senior-most judge of the Supreme Court available) of India is required to officiate till the new President is elected.
This provision was made in 1969 by the Parliament to enable Chief Justice Hidayatullah to officiate when President Zakir Hussain had died, and Vice-President V. V. Giri resigned.
If a President is temporarily unable to discharge his duties, due to illness or otherwise, the Vice-President may discharge the functions of the President without officiating as the President.
When any person, i.e., Vice-President, chief justice of India, or the senior-most judge of the Supreme Court is acting as the President or discharging the functions of the President, he/she enjoys all the powers and immunities of the President and is entitled to such emoluments, allowances and privileges as are determined by the Parliament.