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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 ad-
       dress.  (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  as-
       sociated  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 ad-
       dress 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.

ATTRIBUTES
       For  an  explanation  of  the  terms  used  in  this  section,  see at-
       tributes(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--re-
       turning 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  ad-
       dress  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  ad-
       dresses  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)\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
       bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)

COLOPHON
       This page is part of release 5.05 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                               2019-03-06                     GETIFADDRS(3)

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

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