Can an IP address and port number together identify a process identifier?

Question

Can an IP address and port number together identify a process identifier?

I am looking for a way to get the appropriate process identifier given the IP address and port number, but I'm not sure if such ip / port pairs can uniquely identify one pid.

Answer 1

Not necessary. If the socket is opened or received in the process and then plugged, the child process also has an open socket, so the IP address and port number are used by two processes.

Answer 2

As Jonathan noted, the attitude is not necessarily unique. For example, there are server implementations (apache / prefork) that use child processes to process requests simultaneously.

But you can get a list of processes using a specific port / address in any case (although there may be several entries for one port / address pair), perhaps in your particular case this is a viable solution:

On Windows, for example, you can use the GetExtendedTcpTable function by setting the TableClass parameter to one of the TCP_TABLE_OWNER_MODULE_* values. This returns a table containing the local and remote address / port and process identifier for all current TCP endpoints.

There are similar ways on Linux (although I don’t know by heart how to do this ...), since that’s exactly what netstat -p does.

Answer 3

At that time, only one process can bind to a given port, therefore, given the port, we can listen to no more than one process. Yes, several processes can send and receive through the same port, but only one process is bound to a port.

eg. in the following code appears "server: bind: Address An error is already being used . Then, if we run lsof -i: 2100, we will only get one process identifier listening on port 2100.

 #define SERVERPORT "2100" #define BUF_MAX 1024 #define BACKLOG 10 int data_connection(char* portno) { struct addrinfo hints,*res,*clientinfo; int rv,datafd,yes=1,new_fd; char buf[BUF_MAX]; struct sockaddr_storage their_addr; socklen_t addr_size; memset(&hints,0,sizeof(hints)); hints.ai_family=AF_UNSPEC; hints.ai_socktype=SOCK_STREAM;//connnection oriented. hints.ai_flags=AI_PASSIVE; if ((rv = getaddrinfo(NULL, portno, &hints, &res)) != 0) { fprintf(stderr, "getaddrinfo: %s\n", gai_strerror(rv)); return 1; } for(clientinfo=res;clientinfo!=NULL;clientinfo=clientinfo->ai_next) { if((datafd=socket(clientinfo->ai_family,clientinfo->ai_socktype,clientinfo->ai_protocol))==-1) { perror("server:datasocket"); continue; } break; } if(setsockopt(datafd,SOL_SOCKET,SO_REUSEADDR,&yes,sizeof(int))==-1) { perror("setsockopt"); exit(1); } if(bind(datafd,clientinfo->ai_addr,clientinfo->ai_addrlen)<0) { perror("server:bind"); exit(1); } if(listen(datafd,BACKLOG)<0) { perror("server:listen"); exit(1); } addr_size=sizeof(their_addr); if((new_fd=accept(datafd,(struct sockaddr*)&their_addr,&addr_size))<0) { perror("server:accept"); exit(1); } close(datafd); datafd=new_fd; return datafd; } int main() { int datafd; fork(); datafd=data_connection(SERVERPORT); } 

Answer 4

On a Windows machine, you can get the process ID for the listening application. See this question .