Hello Ion and other Interprocess users, we are currently working with fixed_managed_shared_memory segments and we have a strange behavior while opening existing segments. Sometimes (we did not found the exact scenario yet...), when we try to open a fixed_managed_shared_memory in open_only mode with the code below, we get an interprocess_exception with the an error_code_t = 9 ( already_exists_error ). try{ managedSharedMemorySegment = new fixed_managed_shared_memory(boost::interprocess::open_only, memorySegmentName, memorySegmentMappingAdress); }catch (boost::interprocess::interprocess_exception e){ return e.get_error_code(); } A first sight this error_code seems very strange, because in open_only mode the segment is intended to already exists so that should not be an error. Walking the code I found in the mapped_region constructor the following code which trigger the exception : 522: //Check for fixed mapping error if(address && (old_base != address)){ error_info err = system_error_code(); this->priv_close(); throw interprocess_exception(err); } It seems that the mmap function returns an address different that the given one, which is considered an error. So I have two questions : 1) Do you have an idea why the mmap function maps the segment at a different address from the provided one, knowing that this address is the one returned from code below on another process (so should be valid) ? try{ managedSharedMemorySegment = new fixed_managed_shared_memory(boost::interprocess::create_only, memorySegmentName, memorySegmentSize); memorySegmentMappingAdress = managedSharedMemorySegment->get_address(); }catch (boost::interprocess::interprocess_exception e){ return e.get_error_code(); } 2) In the mapped_region constructor, when a non null address value is given as a parameter, could we use the MAP_FIXED flag to force the mmap function to map the segment at the provided address ? Thank you for reading and for your help. Gaëtan