Проблема прав доступа к семафору

смотри man. там про это есть немного.

Что-то я в man ничего полезного не вижу, подскажи пожалуйста подробнее

написано четко и ясно - 

Upon creation, the low‐order 9 bits of the argument semflg
       define  the  access permissions (for owner, group and oth­
       ers) for the semaphore set.  These bits have the same for­
       mat,  and  the  same  meaning, as the mode argument in the
       open(2) or creat(2) system calls (though the execute  per­
       missions are not meaningful for semaphores, and write per­
       missions mean permission to alter semaphore values).

       When creating a new semaphore set, semget initializes  the
       semaphore set’s associated data structure semid_ds as fol­
       lows:

              sem_perm.cuid  and  sem_perm.uid  are  set  to  the
              effective user−ID of the calling process.

              sem_perm.cgid  and  sem_perm.gid  are  set  to  the
              effective group−ID of the calling process.

              The low‐order 9 bits of sem_perm.mode  are  set  to
              the low‐order 9 bits of semflg.

              sem_nsems is set to the value of nsems.

              sem_otime is set to 0.

              sem_ctime is set to the current time.

       The  argument  nsems  can  be  0  (a  don’t  care)  when a
       semaphore set is not being created.  Otherwise nsems  must
       be  greater  than  0 and less than or equal to the maximum
       number of semaphores per semaphore set (SEMMSL).

       If the semaphore set already exists,  the  access  permis­
       sions are verified.