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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 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  struc-
       tures, 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  net-
       device(7) for a list of these flags).

       The  ifa_addr field points to a structure containing the interface address.  (The sa_family sub-field should be
       consulted to determine the format of the address structure.)

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

       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-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 VALUES
       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  only  sup-
       ported  IPv4  addresses; IPv6 support was added in glibc 2.3.3.  Support of address families other than IPv4 is
       only available 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  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 net_device_stats, defined  in  <linux/netde-
       vice.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 3.22 of the Linux man-pages project.  A description of the project,  and  informa-
       tion about reporting bugs, can be found at http://www.kernel.org/doc/man-pages/.



GNU                               2009-01-23                     GETIFADDRS(3)