Ala. Code § 45-58-231.32: Vacancies.

Whenever a vacancy exists in any position, it shall be filled by appointment of one of the appropriate eligible registrants of the board, or by transfer within the service from another position of the same class. However, any eligible person of the same class who has been laid off, as provided in Section 45–58–231.30, shall receive preference in hiring in every instance. Whenever it is impossible for the board to certify eligible persons to a vacancy, the board may authorize the appointing authority to fill the vacancy temporarily pending the establishment of an eligible registrant. No temporary appointment shall be effective longer than four months, and no such employee shall have protected status under this subpart. All appointments other than temporary appointments shall be probationary for 12 months from the date of appointment. A probationary subordinate employee may be discharged by his or her appointing authority for unsatisfactory service at any time before the expiration of that period. A probationary department head employed may be discharged or demoted similarly by his or her appointing authority upon approval by the board. After the expiration of the probationary period, an appointment shall become permanent, subject to discharge thereafter only for cause.