Get ip server software (Linux)

From the question it is absolutely not clear what exactly is not working.

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Update after the appearance of the code

Your mistakes here

 servlen = sizeof(tmp_addr); // видим struct sockaddr *tmp_addr и похоже это не тот размер -) if(getsockname(sockfd, &sa, &servlen) == -1){ error("ERROR on getsockname"); } tmp_addr_in = (sockaddr_in*)tmp_addr; // этот указатель 

Looks unknown where.

 inet_ntop(AF_INET, &(tmp_addr_in->sin_addr), // вот тут Вам не повезло, прога НЕ УПАЛА (а то, сами бы в отладчике нашли) bufServerIp, INET_ADDRSTRLEN); 

And they are all associated with tmp_addr_in and tmp_addr .

Looks like you just need to write

 servlen = sizeof(sa); if(getsockname(sockfd, &sa, &servlen) == -1){ error("ERROR on getsockname"); } inet_ntop(AF_INET, &((struct sockaddr_in *)&sa)->sin_addr, // видимо тут-то Вы и запутались bufServerIp, INET_ADDRSTRLEN); 

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I would venture to suggest that the variable clilen not initialized before calling accept() .

B man 2 accept is written:

  The addrlen argument is a value-result argument: the caller must ini‐ tialize it to contain the size (in bytes) of the structure pointed to by addr; on return it will contain the actual size of the peer address. 

Those. write:

 socklen_t clilen = (__typeof__(clilen))sizeof(cli_addr); 

before calling accept() (which can change its value).

In addition, having a "legitimate" socket, it does not matter at the client or server, you can always find out as your own address (IP, port)

 int getsockname(int sockfd, struct sockaddr *addr, socklen_t *addrlen); 

so and address "vis"

 int getpeername(int sockfd, struct sockaddr *addr, socklen_t *addrlen); 

In both cases, the addrlen parameter must be initialized before the call (similar to the accept() example) in the buffer size for the address pointed to by *addr .

Here is an example:

 avp@wubu:hashcode$ cat serv-ips.c #include <stdio.h> #include <stdlib.h> #include <string.h> #include <errno.h> #include <unistd.h> #include <sys/types.h> #include <sys/socket.h> #include <netinet/in.h> #include <netdb.h> #include <arpa/inet.h> #define errExit(msg) do { perror(msg); exit(EXIT_FAILURE); \ } while (0) static int makeSimpleServer (char *cport) // default port = 12345 { int on = 1, asock = socket (AF_INET, SOCK_STREAM, 0); if (setsockopt(asock, SOL_SOCKET, SO_REUSEADDR, (char *)&on, sizeof (on)) < 0) errExit("socket"); short port = cport? atoi(cport): 12345; if (port < 1) port = 12345; struct sockaddr_in addr; int laddr = sizeof(addr); memset (&addr, 0, laddr); addr.sin_family = AF_INET; addr.sin_port = htons(port); addr.sin_addr.s_addr = INADDR_ANY; if (bind(asock, (struct sockaddr *)&addr, laddr)) errExit("bind"); struct linger ling; ling.l_onoff = 1; ling.l_linger = 2; // seconds after shudown sock for deliver data if (setsockopt(asock, SOL_SOCKET, SO_LINGER, (char *)&ling, sizeof(ling))) errExit("linger"); if (listen(asock, 128)) errExit("listen"); return asock; } int main (int ac, char *av[]) { // port av[1] (default 12345) and INADDR_ANY int asock = makeSimpleServer(av[1]); int sock; struct sockaddr inadr; socklen_t slen = sizeof(inadr); while ((sock = accept(asock, &inadr, &slen)) > 0) { printf ("New connection %s:%d\n", inet_ntoa(((struct sockaddr_in *)&inadr)->sin_addr), ntohs(((struct sockaddr_in *)&inadr)->sin_port)); if (getpeername(sock, &inadr, &slen) == -1) perror("getpeername"); else printf("getpeername %s:%d\n", inet_ntoa(((struct sockaddr_in *)&inadr)->sin_addr), ntohs(((struct sockaddr_in *)&inadr)->sin_port)); if (getsockname(sock, &inadr, &slen) == -1) perror("getsockname"); else printf("getsockname %s:%d\n", inet_ntoa(((struct sockaddr_in *)&inadr)->sin_addr), ntohs(((struct sockaddr_in *)&inadr)->sin_port)); close(sock); errno = 0; } perror("server exit"); } avp@wubu:hashcode$ gcc serv-ips.c && ./a.out New connection 10.3.35.78:46980 getpeername 10.3.35.78:46980 getsockname 10.3.35.78:12345 New connection 127.0.0.1:50958 getpeername 127.0.0.1:50958 getsockname 127.0.0.1:12345 ^C avp@wubu:hashcode$ 

in another window, respectively, ran

 avp@wubu:~$ nc 10.3.35.78 12345 avp@wubu:~$ nc localhost 12345 

As you can see, everything works for me.

Update

Considered that you have a problem with calling inet_ntop() ...
According to man inet_ntop

 The resulting string is copied to the buffer pointed to by dst, which must be a non-null pointer. The caller specifies the number of bytes available in this buffer in the argument size. 

....

  AF_INET src points to a struct in_addr (in network byte order) which is converted to an IPv4 network address in the dotted-decimal format, "ddd.ddd.ddd.ddd". The buffer dst must be at least INET_ADDRSTRLEN bytes long. 

In the example code, it should be called like this:

 char buf[64]; inet_ntop(AF_INET, &((struct sockaddr_in *)&inadr)->sin_addr, buf, sizeof(buf) - 1) 

I checked, really the results are the same as when calling inet_ntoa(...)