Linux named sockets howto
A Unix/Linux socket file is basically a two-way FIFO.
Since sockets were originally created
as a way to manage network communications,
it is possible to manipulate them
using the send()
and recv()
system calls.
However, in the Unix spirit of “everything is a file”,
you can also use write()
and read()
.
You need to use socketpair()
or socket()
to create named sockets.
A tutorial for using sockets in C can be found here:
Beej's Guide to Unix IPC: Unix Sockets.
The socat
command line utility is useful when you want to play around with sockets without writing a "real" program. It is similar to netcat
and acts as an adapter between different networking and file interfaces.
Links:
socat
project home- An introduction to
socat
- Interesting article about Unix sockets and
socat
Create a socket quickly in python:
~]# python -c "import socket as s; sock = s.socket(s.AF_UNIX); sock.bind('/tmp/somesocket')"
~]# ll /tmp/somesocket
srwxr-xr-x. 1 root root 0 Mar 3 19:30 /tmp/somesocket
Or with a tiny C program, e.g., save the following to create-a-socket.c
:
#include <fcntl.h>
#include <sys/un.h>
#include <sys/socket.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <unistd.h>
int main(int argc, char **argv)
{
// The following line expects the socket path to be first argument
char * mysocketpath = argv[1];
// Alternatively, you could comment that and set it statically:
//char * mysocketpath = "/tmp/mysock";
struct sockaddr_un namesock;
int fd;
namesock.sun_family = AF_UNIX;
strncpy(namesock.sun_path, (char *)mysocketpath, sizeof(namesock.sun_path));
fd = socket(AF_UNIX, SOCK_DGRAM, 0);
bind(fd, (struct sockaddr *) &namesock, sizeof(struct sockaddr_un));
close(fd);
return 0;
}
Then install gcc, compile it, and ta-da:
~]# gcc -o create-a-socket create-a-socket.c
~]# ./create-a-socket mysock
~]# ll mysock
srwxr-xr-x. 1 root root 0 Mar 3 17:45 mysock