The Secretariat - Appointment of the secretary-general
Since the charter does not specify the qualifications for Secretary-General and the term of office, these decisions had to be made by the first General Assembly, in January 1946. It was agreed that, in making its recommendations to the General Assembly, the Security Council should conduct its discussions in private and vote in secret, for the dignity of the office required avoidance of open debate on the qualifications of the candidate. The General Assembly also decided that the term of office would be five years (the Secretary-General of the League of Nations was elected for 10 years) and that the Secretary-General would be eligible for reappointment.
The permanent members of the Security Council have tacitly agreed that the Secretary-General should not be a national of one of their own countries.