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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.)

       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  supported  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/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 3.35 of the Linux man-pages project.  A description of the
       project, and information about reporting bugs, can be found at  http://man7.org/linux/man-
       pages/.