getifaddrs(3) — Linux manual page


getifaddrs(3)           Library Functions Manual           getifaddrs(3)

NAME         top

       getifaddrs, freeifaddrs - get interface addresses

LIBRARY         top

       Standard C library (libc, -lc)

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

       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 to indicate the error.

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).

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ Interface                           Attribute     Value   │
       │ getifaddrs(), freeifaddrs()         │ Thread safety │ MT-Safe │

STANDARDS         top


HISTORY         top

       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.

       getifaddrs() 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.

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.

EXAMPLES         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: <>
           wlp3s0   AF_INET (2)
                           address: <>
           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;
           int family, s;
           char host[NI_MAXHOST];

           if (getifaddrs(&ifaddr) == -1) {

           /* Walk through linked list, maintaining head pointer so we
              can free list later. */

           for (struct ifaddrs *ifa = ifaddr; ifa != NULL;
                    ifa = ifa->ifa_next) {
               if (ifa->ifa_addr == NULL)

               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",
                      (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));

                   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);


SEE ALSO         top

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

COLOPHON         top

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Linux man-pages 6.9.1          2024-06-15                  getifaddrs(3)

Pages that refer to this page: bind(2)getsockname(2)if_nameindex(3)if_nametoindex(3)