The mayor shall qualify and take office in the manner herein prescribed. The regular election for mayor shall be held quadrennially thereafter under the same rules and regulations and in the same mode and manner herein provided. The mayor elected at such regular election shall qualify by making oath that he is eligible for said office and will execute the duties of same according to the best of his knowledge and ability. Said oath may be administered by any person authorized to administer an oath under the laws of Alabama. A mayor may succeed himself.