NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | EXAMPLE | SEE ALSO | COLOPHON

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

NAME         top

       getifaddrs, freeifaddrs - get interface addresses

SYNOPSIS         top

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

       int getifaddrs(struct ifaddrs **ifap);

       void freeifaddrs(struct ifaddrs *ifa);

DESCRIPTION         top

       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
       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 VALUE         top

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

ERRORS         top

       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         top

       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         top

       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         top

       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         top

       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)\n",
                      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\n", gai_strerror(s));
                       exit(EXIT_FAILURE);
                   }

                   printf("\t\taddress: <%s>\n", host);

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

                   printf("\t\ttx_packets = %10u; rx_packets = %10u\n"
                          "\t\ttx_bytes   = %10u; rx_bytes   = %10u\n",
                          stats->tx_packets, stats->rx_packets,
                          stats->tx_bytes, stats->rx_bytes);
               }
           }

           freeifaddrs(ifaddr);
           exit(EXIT_SUCCESS);
       }

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 3.75 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
       http://www.kernel.org/doc/man-pages/.

GNU                              2014-02-26                    GETIFADDRS(3)