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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 describ‐
       ing 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 destination
       address of the point-to-point interface.

       The ifa_data field points to a  buffer  containing  address-family-spe‐
       cific  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), malloc(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 support
       was added in glibc 2.3.3.  Support of address families other than  IPv4
       is available only on kernels that support netlink.

CONFORMING TO
       Not  in	POSIX.1-2001.	This  function	first  appeared in BSDi and is
       present on the BSD systems, but with slightly different semantics docu‐
       mented—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	   address family: 17 (AF_PACKET)
	   eth0	   address family: 17 (AF_PACKET)
	   lo	   address family: 2 (AF_INET)
		   address: <127.0.0.1>
	   eth0	   address family: 2 (AF_INET)
		   address: <10.1.1.4>
	   lo	   address family: 10 (AF_INET6)
		   address: <::1>
	   eth0	   address family: 10 (AF_INET6)
		   address: <fe80::2d0:59ff:feda:eb51%eth0>

   Program source

       #include <arpa/inet.h>
       #include <sys/socket.h>
       #include <netdb.h>
       #include <ifaddrs.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <unistd.h>

       int
       main(int argc, char *argv[])
       {
	   struct ifaddrs *ifaddr, *ifa;
	   int family, s;
	   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; ifa != NULL; ifa = ifa->ifa_next) {
	       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("%s  address family: %d%s\n",
		       ifa->ifa_name, family,
		       (family == AF_PACKET) ? " (AF_PACKET)" :
		       (family == AF_INET) ?   " (AF_INET)" :
		       (family == AF_INET6) ?  " (AF_INET6)" : "");

	       /* 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\n", gai_strerror(s));
		       exit(EXIT_FAILURE);
		   }
		   printf("\taddress: <%s>\n", host);
	       }
	   }

	   freeifaddrs(ifaddr);
	   exit(EXIT_SUCCESS);
       }

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

COLOPHON
       This  page  is  part of release 3.54 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

GNU				  2012-11-11			 GETIFADDRS(3)
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