The powers and duties of the commission shall be as follows:

  (a) It shall classify all the offices and positions of employment with reference to the examinations herein provided for, excepting as herein otherwise provided;

  (b) Shall from time to time make, in accordance with the provisions hereof, rules adapted to carry out the purposes of this act and not inconsistent with its provisions for the examination and selection of persons to fill the offices and positions in the classified service, which are required to be filled by appointment, and for the selection of persons to be employed in the service of the county;

  (c) Shall supervise the administration of the civil service rules, hold examinations thereunder from time to time, giving notice thereof, prepare and keep an eligible list of persons passing such examinations and certify the names of persons thereon to the appointing officers of the several departments;

  (d) Shall, by itself or otherwise, investigate the enforcement of the provisions of this act, of its own rules and of the action of appointees in the classified service. In the course of such investigation, the commission or its authorized representative, shall have the power to administer oaths, and the commission shall have power by its subpoena, to secure, both the attendance and testimony of witnesses and the production of books and papers relevant to such investigations;

  (e) Shall provide, through the purchasing department of the county, all needed supplies for the use of the commission;

  (f) The classification shall be subdivided into groups and shall be based upon, and graded according to the duties and responsibilities of such positions, and shall be so arranged as to permit the filling of the higher grades through promotion. All salaries shall be uniform for like service in each grade of the classified service as the same shall be classified and standardized by the commission. Such classification and standardization of salaries shall not be final until approved by the board of supervisors, and such salaries shall not be paid except in accordance with such classification and standardization;

  (g) Shall have such other powers and perform such other duties as may be necessary to carry out the provisions hereof.

   It shall prepare and hold open competitive examinations in order to test the relative fitness of all applicants for appointment to the classified service. At least 2 weeks’ notice shall be given of all such examinations.

   It shall cause to be kept in each department and division thereof, records of the service of each employee, known as “service records”. These records shall contain fact statements on all matters relating to the character and quality of the work done and the attitude of the individual to his work.

   It shall keep a roster of the employees of the county, together with a record of service, military or naval experience and such other matters as may have a bearing on promotion, transfer or discharge. All such “service records” and employees’ records shall be confidential and not open for public inspection.

   Anything in this act to the contrary notwithstanding, the commission, upon the recommendation of the appointing authority, may grant regular status in the class of common laborer to any employee who has completed at least 12 months continuous satisfactory employment in the county service as a provisional laborer in accordance with such rules and regulations as shall be established by the commission.