how to proceed legally if common man beaten by public servant without reason or orders?

he can file FIR

Another option is to file a private complaint in the court of the judicial first class magistrate having jurisdiction.

There's no question of sanction because beating is not a duty.

But judiciary is a strong wall with holes through which public servants and bribers escape with utmost ease.

I expected commendation.    At least condemnation hasn't issued.

It's a surprise why members are uninterested.    Perhaps because they're not disinterested.

Section 197(1) of the Criminal Procedure Code reads, ....while acting or purporting to act in discharge of his official duty... 

Beating is not his official duty.

Hence sanction is unwarranted.

TEHNICALLY, I agree with Expert "TGK REDDI":

1. You can file a Police NC, requesting investigation and charge-sheet, for offences like intimidation, breach of trust etc.... against the person, supported with all relevant supporting documents /witnesses.  Alongwith above MUST file written notice to Police Commissioner /SP, against the nefarious Police person, and request to take departmental action.

2.  IF the Police does not take action on the NC & Notice, THEN you can file private criminal case u/s 156(3) Cr.P.C., in the local Magistrates court, seeking directions to the Police to investigate and file charge sheet. IF at all "any" permission is required, the Police dept., will do so, without any reference to the complainant /aggrived person.

Keep Smiling .... Hemant Agarwal
VISIT: www.chshelpforum.com

The contention is whether sanction is necessry.

I maintain it is not, it is not, it is not.