getifaddrs, freeifaddrs - get interface addresses
#include <sys/types.h>
#include <ifaddrs.h>
int getifaddrs(struct ifaddrs **ifap);
void freeifaddrs(struct ifaddrs *ifa);
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.
On success, getifaddrs() returns zero; on error, -1
is returned, and errno
is set appropriately.
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>
#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) {
perror("getifaddrs");
exit(EXIT_FAILURE);
}
/* 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)
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);
}
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).
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.
For an explanation of the terms used in this section, see attributes(7).
Interface | Attribute | Value |
getifaddrs(), freeifaddrs() | Thread safety | MT-Safe |
Not in POSIX.1. 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.
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.
bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)
This page is part of release 5.10 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/.