|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|
|
NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | ATTRIBUTES | STANDARDS | HISTORY | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
|
|
|
getifaddrs(3) Library Functions Manual getifaddrs(3)
getifaddrs, freeifaddrs - get interface addresses
Standard C library (libc, -lc)
#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 to indicate the error.
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).
For an explanation of the terms used in this section, see
attributes(7).
┌─────────────────────────────────────┬───────────────┬─────────┐
│ Interface │ Attribute │ Value │
├─────────────────────────────────────┼───────────────┼─────────┤
│ getifaddrs(), freeifaddrs() │ Thread safety │ MT-Safe │
└─────────────────────────────────────┴───────────────┴─────────┘
None.
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.
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.
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;
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);
}
bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
[email protected]
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)
|
HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|