How to get IP Address of machine? Post: 41691

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Top Forums Programming How to get IP Address of machine? Post 41691 by Perderabo on Sunday 12th of October 2003 12:37:27 AM

10-12-2003

Administrator Emeritus

Re: bump

Quote:

Originally posted by DreamWarrior
Hey, could you all be a bit more specific on this one. I read the man page for gethostbyname and it seems to be returning a generic internal address format. That needs to be converted into a dot notation IP address, and I don't know how to do it.

The best solution to stuff like this is to browse some source code. There is a ton of source code on the internet. And there are several programs that format ip addresses. But I'm trapped at the office waiting for a tech, and I don't have anything better to do, so...

Code:

#ifdef __STDC__
#define PROTOTYPICAL
#endif
#ifdef __cplusplus
#define PROTOTYPICAL
#endif

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <netdb.h>
#include <arpa/inet.h>


#ifdef PROTOTYPICAL
int main(int argc, char *argv[])
#else
main(argc,argv)
char *argv[];
#endif
{
	char *mess;
	struct hostent *hp;
	int dumpall;

	dumpall=0;
	while(*++argv) {
		if(!strcmp(*argv,(char *)"-d")) {
			dumpall=!dumpall;
			continue;
		}
		/*
		 *  Call gethostbyname for current argument
		 */
		if(! (hp = gethostbyname(*argv))) {
			switch(h_errno){
					case HOST_NOT_FOUND:  
						mess=(char *)"Not Found";
						break;
					case TRY_AGAIN:  
						mess=(char *)"Time Out";
						break;
					case NO_RECOVERY:  
						mess=(char *)"No Recovery";
						break;
					case NO_ADDRESS:  
						mess=(char *)"No Address";
						break;
					default: 
						mess=(char *)"unknown error";
						break;
			}
			printf("%s  %s\n", *argv, mess);

		} else {
			printf("%s  %s  %s \n", *argv, hp->h_name,
				inet_ntoa(*(struct in_addr *)(hp->h_addr)));
			if(dumpall) {
				printf("  addresses:\n");
				while(*(hp->h_addr_list)){
					printf("      %s \n", 
						inet_ntoa(*(struct in_addr *)*(hp->h_addr_list)++));
				}
				printf("  aliases:\n");
				while(*(hp->h_aliases)){
					printf("      %s \n",*(hp->h_aliases)++);
				} 
			}
		}
	}
	exit(0);
}

This should work with any c or c++ compiler. But I only tested on HP-UX.

Quote:

Originally posted by DreamWarrior

Also, to extend this a bit, is it possible to obtain the information starting from a file descriptor that is a socket. I.E. if the only piece of information I have about the connection is the file descriptor, can I get the sockaddr_in structure from that to pass to gethostbyname to then convert into an IP?

Thanks!

Yow!! We have 4 hour response time.

You cannot do that portably and it usually requires root power. Look at the source code for lsof. It does stuff like that.

But all sockets structures store ip address not domain names

Perderabo

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LEARN ABOUT DEBIAN

systemd-machine-id-commit.service

SYSTEMD-MACHINE-ID-COMMIT.SERVICE(8)			 systemd-machine-id-commit.service		      SYSTEMD-MACHINE-ID-COMMIT.SERVICE(8)

NAME

       systemd-machine-id-commit.service - Commit a transient machine ID to disk

SYNOPSIS

       systemd-machine-id-commit.service

DESCRIPTION

       systemd-machine-id-commit.service is an early boot service responsible for committing transient /etc/machine-id files to a writable disk
       file system. See machine-id(5) for more information about machine IDs.

       This service is started after local-fs.target in case /etc/machine-id is a mount point of its own (usually from a memory file system such
       as "tmpfs") and /etc is writable. The service will invoke systemd-machine-id-setup --commit, which writes the current transient machine ID
       to disk and unmount the /etc/machine-id file in a race-free manner to ensure that file is always valid and accessible for other processes.
       See systemd-machine-id-setup(1) for details.

       The main use case of this service are systems where /etc/machine-id is read-only and initially not initialized. In this case, the system
       manager will generate a transient machine ID file on a memory file system, and mount it over /etc/machine-id, during the early boot phase.
       This service is then invoked in a later boot phase, as soon as /etc has been remounted writable and the ID may thus be committed to disk to
       make it permanent.

SEE ALSO

       systemd(1), systemd-machine-id-setup(1), machine-id(5), systemd-firstboot(1)

systemd 237												      SYSTEMD-MACHINE-ID-COMMIT.SERVICE(8)

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