When invoked with port/proto instead of a file, fuser.c calls access() to check for the file /proc/net/<proto>. It checks for a non-zero return from access().  But if the file is accessible, the return is zero, not non-zero!


int fuser_main(int argc UNUSED_PARAM, char **argv)
{
    .....

    if (access(path, R_OK) != 0) { /* PORT/PROTO */
        scan_proc_net(path, port);
    } else { /* FILE */
 file:
        xstat(*pp, &st);
        add_inode(&st);
    }
    .....
}