The clock_getcpuclockid() function shall return the clock ID of the CPU-time clock of the process specified by pid. If the process described by pid exists and the calling process has permission, the clock ID of this clock shall be returned in clock_id. If pid is zero, the clock_getcpuclockid() function shall return the clock ID of the CPU-time clock of the process making the call, in clock_id. clock_getcpuclockid() returns 0 on success. The clock_getcpuclockid() function shall fail and return EPERM if the requesting process does not have permission to access the CPU-time clock for the process. The clock_getcpuclockid() function may fail and return ESRCH if no process can be found corresponding to the process specified by pid.