GETIFADDRS(3)						     Linux Programmer's Manual						     GETIFADDRS(3)

NAME

       getifaddrs, freeifaddrs - get interface addresses

SYNOPSIS

       #include <sys/types.h>
       #include <ifaddrs.h>

       int getifaddrs(struct ifaddrs **ifap);

       void freeifaddrs(struct ifaddrs *ifa);

DESCRIPTION

       The getifaddrs() function creates a linked list of structures describing the network interfaces of the local system, and stores the address
       of the first item of the list in *ifap.	The list consists of ifaddrs structures, defined as follows:

	   struct ifaddrs {
	       struct ifaddrs  *ifa_next;    /* Next item in list */
	       char	       *ifa_name;    /* Name of interface */
	       unsigned int	ifa_flags;   /* Flags from SIOCGIFFLAGS */
	       struct sockaddr *ifa_addr;    /* Address of interface */
	       struct sockaddr *ifa_netmask; /* Netmask of interface */
	       union {
		   struct sockaddr *ifu_broadaddr;
				    /* Broadcast address of interface */
		   struct sockaddr *ifu_dstaddr;
				    /* Point-to-point destination address */
	       } ifa_ifu;
	   #define		ifa_broadaddr ifa_ifu.ifu_broadaddr
	   #define		ifa_dstaddr   ifa_ifu.ifu_dstaddr
	       void	       *ifa_data;    /* Address-specific data */
	   };

       The ifa_next field contains a pointer to the next structure on the list, or NULL if this is the last item of the list.

       The ifa_name points to the null-terminated interface name.

       The ifa_flags field contains the interface flags, as returned by the SIOCGIFFLAGS ioctl(2) operation (see netdevice(7) for a list of  these
       flags).

       The  ifa_addr  field  points to a structure containing the interface address.  (The sa_family subfield should be consulted to determine the
       format of the address structure.)  This field may contain a null pointer.

       The ifa_netmask field points to a structure containing the netmask associated with ifa_addr, if applicable for the  address  family.   This
       field may contain a null pointer.

       Depending  on  whether  the  bit IFF_BROADCAST or IFF_POINTOPOINT is set in ifa_flags (only one can be set at a time), either ifa_broadaddr
       will contain the broadcast address associated with ifa_addr (if applicable for the address family) or ifa_dstaddr will contain the destina-
       tion address of the point-to-point interface.

       The  ifa_data  field  points  to a buffer containing address-family-specific data; this field may be NULL if there is no such data for this
       interface.

       The data returned by getifaddrs() is dynamically allocated and should be freed using freeifaddrs() when no longer needed.

RETURN VALUE

       On success, getifaddrs() returns zero; on error, -1 is returned, and errno is set appropriately.

ERRORS

       getifaddrs() may fail and set errno for any of the errors specified for socket(2), bind(2),  getsockname(2),  recvmsg(2),  sendto(2),  mal-
       loc(3), or realloc(3).

VERSIONS

       The  getifaddrs() function first appeared in glibc 2.3, but before glibc 2.3.3, the implementation supported only IPv4 addresses; IPv6 sup-
       port was added in glibc 2.3.3.  Support of address families other than IPv4 is available only on kernels that support netlink.

ATTRIBUTES

       For an explanation of the terms used in this section, see attributes(7).

       +----------------------------+---------------+---------+
       |Interface		    | Attribute     | Value   |
       +----------------------------+---------------+---------+
       |getifaddrs(), freeifaddrs() | Thread safety | MT-Safe |
       +----------------------------+---------------+---------+

CONFORMING TO

       Not in POSIX.1.	This function first appeared in BSDi and is present on the BSD systems, but with slightly different semantics documented--
       returning  one  entry  per  interface,  not per address.  This means ifa_addr and other fields can actually be NULL if the interface has no
       address, and no link-level address is returned if the interface has an IP address assigned.  Also, the way of choosing either ifa_broadaddr
       or ifa_dstaddr differs on various systems.

NOTES

       The  addresses  returned on Linux will usually be the IPv4 and IPv6 addresses assigned to the interface, but also one AF_PACKET address per
       interface containing lower-level details about the interface and its physical layer.  In this  case,  the  ifa_data  field  may	contain  a
       pointer	to  a  struct  rtnl_link_stats,  defined  in  <linux/if_link.h>  (in  Linux  2.4  and earlier, struct net_device_stats, defined in
       <linux/netdevice.h>), which contains various interface attributes and statistics.

EXAMPLE

       The program below demonstrates the use of getifaddrs(), freeifaddrs(), and getnameinfo(3).  Here is what we see when running  this  program
       on one system:

	   $ ./a.out
	   lo	    AF_PACKET (17)
			   tx_packets =        524; rx_packets =	524
			   tx_bytes   =      38788; rx_bytes   =      38788
	   wlp3s0   AF_PACKET (17)
			   tx_packets =     108391; rx_packets =     130245
			   tx_bytes   =   30420659; rx_bytes   =   94230014
	   em1	    AF_PACKET (17)
			   tx_packets = 	 0; rx_packets =	  0
			   tx_bytes   = 	 0; rx_bytes   =	  0
	   lo	    AF_INET (2)
			   address: <127.0.0.1>
	   wlp3s0   AF_INET (2)
			   address: <192.168.235.137>
	   lo	    AF_INET6 (10)
			   address: <::1>
	   wlp3s0   AF_INET6 (10)
			   address: <fe80::7ee9:d3ff:fef5:1a91%wlp3s0>

   Program source

       #define _GNU_SOURCE     /* To get defns of NI_MAXSERV and NI_MAXHOST */
       #include <arpa/inet.h>
       #include <sys/socket.h>
       #include <netdb.h>
       #include <ifaddrs.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>
       #include <linux/if_link.h>

       int main(int argc, char *argv[])
       {
	   struct ifaddrs *ifaddr, *ifa;
	   int family, s, n;
	   char host[NI_MAXHOST];

	   if (getifaddrs(&ifaddr) == -1) {
	       perror("getifaddrs");
	       exit(EXIT_FAILURE);
	   }

	   /* Walk through linked list, maintaining head pointer so we
	      can free list later */

	   for (ifa = ifaddr, n = 0; ifa != NULL; ifa = ifa->ifa_next, n++) {
	       if (ifa->ifa_addr == NULL)
		   continue;

	       family = ifa->ifa_addr->sa_family;

	       /* Display interface name and family (including symbolic
		  form of the latter for the common families) */

	       printf("%-8s %s (%d)
",
		      ifa->ifa_name,
		      (family == AF_PACKET) ? "AF_PACKET" :
		      (family == AF_INET) ? "AF_INET" :
		      (family == AF_INET6) ? "AF_INET6" : "???",
		      family);

	       /* For an AF_INET* interface address, display the address */

	       if (family == AF_INET || family == AF_INET6) {
		   s = getnameinfo(ifa->ifa_addr,
			   (family == AF_INET) ? sizeof(struct sockaddr_in) :
						 sizeof(struct sockaddr_in6),
			   host, NI_MAXHOST,
			   NULL, 0, NI_NUMERICHOST);
		   if (s != 0) {
		       printf("getnameinfo() failed: %s
", gai_strerror(s));
		       exit(EXIT_FAILURE);
		   }

		   printf("		address: <%s>
", host);

	       } else if (family == AF_PACKET && ifa->ifa_data != NULL) {
		   struct rtnl_link_stats *stats = ifa->ifa_data;

		   printf("		tx_packets = %10u; rx_packets = %10u
"
			  "		tx_bytes   = %10u; rx_bytes   = %10u
",
			  stats->tx_packets, stats->rx_packets,
			  stats->tx_bytes, stats->rx_bytes);
	       }
	   }

	   freeifaddrs(ifaddr);
	   exit(EXIT_SUCCESS);
       }

SEE ALSO

       bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)

COLOPHON

       This  page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

GNU
								    2017-09-15							     GETIFADDRS(3)