Rugg, C.J.
This is a petition for a writ of certiorari to quash the proceedings of the respondent taken by him upon a petition against William Johnson, mayor of the city of North Adams, whereby there -was sought review of the action by the said mayor in removing the petitioner as a police officer of the city of North Adams, and his reinstatement as such police officer. The return of the respondent sets out a copy of that petition for review as amended,- and all proceedings thereon. The return must be taken to set out an accurate record of the proceedings and to be true and conclusive as to all matters of fact within the jurisdiction of the respondent. It is not open to contradiction. Westport v. County Commissioners, 246 Mass. 556, 562. It thus appears that charges had been preferred to the mayor against the petitioner by his superior officer, and that on October 9, 1928, the mayor notified the peti*458tioner in writing that he contemplated removing him from office as one of the police officers of the city of North Adams on Saturday, October 13, 1928, at two o’clock in the afternoon, specifying at the same time in detail twenty-two charges made against him. This notification bearing the heading “City of North Adams Massachusetts Office of the Mayor” was served by a deputy sheriff and with copy of the sheriff’s return was filed with the city clerk. The petitioner did not appear either personally or by counsel before the mayor on October 13, 1928, or at any other time. The mayor later on that day removed him from office and sent to the petitioner written notice that the charges stated in the letter of October 9 had been found to be sustained and that for those reasons he had been removed. The mayor also caused to be filed with the city clerk a signed statement to the same effect. Seasonably thereafter the petitioner brought his petition for review in the District Court for Northern Berkshire. After hearing upon such petition for review the respondent filed a decision in which, after a considerable recital of facts found, he stated his final decision in these words: “The evidence shows there was information furnished the Mayor from sources which he considered reliable, which amply justified his finding the charges sustained to such an extent as to warrant the removal of the petitioner, and the petitioner’s failure to appear in his own defense warrants inferences unfavorable to his interests. I therefore find that the action of removal complained of was justified and is hereby affirmed.”
It is provided by § 42B, added to G. L. c. 31 by St. 1923, c. 242, § 1, that upon such petition for review the “decision of the court shall be final and conclusive upon the parties.” Nevertheless it was not the legislative intent thereby to deprive parties of the beneficent remedy afforded by the extraordinary writ of certiorari if there are substantial errors of law apparent on the record adversely affecting their material rights. McLaughlin v. Mayor of Cambridge, 253 Mass. 193, 199, 200, and cases there cited.
The function of a writ of certiorari is to annul proceed*459ings of a judicial or quasi judicial tribunal not otherwise reviewable which show on their face a defect as matter of law so substantial in nature as to make it manifest that justice requires the writ to issue in order to prevent a material wrong. It does not issue on account of formal or technical errors or those which have not resulted in manifest injustice to the petitioner or which have not adversely affected the real interests of the general public. Swan v. Justices of the Superior Court, 222 Mass. 542, 546. Mayor of Medford v. Judge of the District Court, 249 Mass. 465, 468. Roman Catholic Archbishop of Boston v. Board of Appeal of Boston, 268 Mass. 416, 419. The writ does not issue as matter of right but rests in sound judicial discretion. It will not be granted unless the petitioner demonstrates that substantial justice requires it even though defects of some comparatively inconsequential nature may appear on the record. Sears v. Mayor & Aldermen of Worcester, 180 Mass. 288, and cases cited. Corcoran v. Aldermen of Cambridge, 199 Mass. 5, 14.
It is apparent from the decision filed by the respondent that he undertook scrupulously to follow the principles of law laid down in Selectmen of Wakefield v. Judge of the District Court, 262 Mass. 477,481,482,483. Those principles need not be restated. On that petition it was the duty of the respondent under said § 42B to examine the action of the mayor, hear any or all of the witnesses, and determine whether upon the evidence presented to him the action of the mayor in removing the petitioner was justified.
The first contention of the petitioner is that the proceedings should be quashed for the reason that the respondent ought to have ruled that there was no compliance by the mayor with the statutory requirement that the petitioner as police officer could not be removed “except after a full hearing of which he shall have at least seventy-two hours’ written notice.” § 42A added to said c. 31 by St. 1923, c. 242, § 1, and amended by St. 1925, c. 220, § 2. He complains especially of the ruling of the respondent that although the notice given to the petitioner by the mayor was informal and “clearly should have stated that a hearing upon *460the charges filed would be held at a definite time and place,” yet because that notice contained charges accusing him of twenty-two distinct and grave derelictions of duty, he must have realized the seriousness of the matter and that it was reasonable to infer that he knew from this notice that the mayor contemplated consideration of action upon these charges at his office at the city hall at the hour named in the notice. So far as this was a finding of fact, of course it is not open to review. We cannot say that it contains any .erroneous ruling of law. Under the statute as at present phrased the petitioner could not be removed except after hearing preceded by a notice with statement of reasons. The notice in question indubitably was served a sufficient length of time before the time stated therein. Any attempt by the mayor to remove the petitioner from his office without a hearing and without notice would have been futile under the statute. Stiles v. Municipal Council of Lowell, 233 Mass. 174, 180, 181. The removal of a police officer is a quite different thing from a temporary suspension without notice, when necessary as matter of police discipline, for just cause and for reasons to be given in writing within twenty-four hours after such suspension, also permissible under said § 42A. The two cannot well be confused on reading that section. In these circumstances the inference is permissible that the petitioner had just cause to believe that at the time and place mentioned in the notice the mayor intended to do whatever was necessary as a prerequisite to his removal, provided a finding was made after hearing that the charges specified in the notice were sustained. The charges against the petitioner were of flagitious personal and official misconduct. They would naturally be resented by an honest man who would avail himself of every reasonable opportunity to prove their falsity. Attorney General v. Pelletier, 240 Mass. 264, 316, 323. In view of all the attendant conditions the finding was warranted that the petitioner, after the notice was served upon him, as a reasonable man ought to have inferred that the purpose of the notice was to give him an opportunity to be heard upon the charges stated therein at the time designated and at the office of the mayor in the *461city hall. The whole purpose of the statutory requirement for a preliminary notice with statement of reasons and a hearing is to give to a person of the class to which the petitioner belonged an opportunity to defend himself against the proposed charges and to have a fair hearing. If the mayor as an executive officer was thought to be partisan, it was still the duty of the petitioner to appear before that officer and present his evidence. Thus the foundation would be laid for a review by the disinterested judicial tribunal designated in the statute. The design of the civil service law is to free competent and upright public servants from arbitrary removal but not by the requirement of insubstantial formalities to shield the inefficient or unworthy from being separated from the public service. McCarthy v. Commonwealth, 204 Mass. 482, 486. O’Brien v. Cadogan, 220 Mass. 578. There is nothing inconsistent with this conclusion in cases like Ransom v. Boston, 196 Mass. 248.
The petitioner further contends that it is apparent from the finding of the respondent that no legal evidence was presented to the mayor on October 13 to support the charges made and to warrant his removal. The petitioner did not appear at that time. Thereby he waived the right himself to hear the testimony of witnesses and to cross-examine them. The mayor had interviewed many of the witnesses, and had received their direct statements in substantiation of the charges. The chief of police was ready to produce at the hearing before the mayor witnesses to support the charges. He had personal knowledge as to many facts of that nature which he had communicated to the mayor. It is not essential that the hearing before the mayor be according to strict evidentiary procedure provided substantial justice is done. Swan v. Justices of the Superior Court, 222 Mass. 542, 548. At the time appointed the mayor, chief of police and city solicitor were present at the office of the mayor. When it became obvious that the petitioner had not appeared, the city solicitor advised that the mayor and the chief of police go over the charges in a formal way. The latter recounted *462the fact that he had gone over the charges several times with the mayor and was ready to call witnesses. At the hearing before the respondent the mayor and the chief of police testified. At that hearing all the information in the possession of the mayor at the time of removal was presented by testimony. The respondent, under a ruling that by said § 42B he was bound to review the entire action of the mayor in removing the petitioner from office, received testimony as to what knowledge the mayor acquired touching the charges before they were filed with him and before the time appointed for a hearing by him. In view of all unreported evidence thus received the respondent made the finding hereinbefore quoted. It is not necessary to examine with nicety the questions of law thus raised as to testimony received and as to procedure. The underlying factors are these: the petitioner was removed from office upon charges showing serious misconduct; he did not appear before the mayor at the time and place afforded for refutation of those charges; that of itself warrants inferences unfavorable to him; at the hearing before the respondent upon the petition for review he merely objected to various steps; the respondent as an impartial judicial magistrate has found that the action of the mayor in removing the petitioner was justified; the petitioner now seeks to have these proceedings quashed. In substance and effect the mayor as an executive officer and the respondent as a- judge, in separate proceedings and acting independently, in finding the charges sustained or justified have declared that the' petitioner was unfit to be and to remain a police officer. In these circumstances the judicial discretion of the single justice was rightly exercised in refusing to put forth the extraordinary power of the court in favor of the petitioner. It is manifest that the petitioner has no genuine right to remain or to be reinstated as a police officer. Even though meticulous examination of every part of the proceedings might reveal some deviations from strict regularity or technical accuracy, the overwhelming consideration of want of genuine harm or sub*463stantial injustice to the petitioner does not require the quashing of the proceedings of the respondent. In a case like the present the interest of the public welfare also is entitled to be weighed in the balance to determine whether sound judicial discretion ought to be exercised in favor of the petitioner. Hancock v. Boston, 1 Met. 122, 123. Stone v. Boston, 2 Met. 220, 228. Pickford v. Mayor & Aldermen of Lynn, 98 Mass. 491, 496. Farmington River Water Power Co. v. County Commissioners, 112 Mass. 206, 212. Pigeon’s Case, 216 Mass. 51, 55. Byfield v. Newton, 247 Mass. 46, 58.
Exceptions overruled.