1GETIFADDRS(3) Linux Programmer's Manual GETIFADDRS(3)
2
6 getifaddrs, freeifaddrs - get interface addresses
7
9 #include <sys/types.h>
10 #include <ifaddrs.h>
11 int getifaddrs(struct ifaddrs **ifap);
13 void freeifaddrs(struct ifaddrs *ifa);
15
17 The getifaddrs() function creates a linked list of structures describ‐
18 ing the network interfaces of the local system, and stores the address
19 of the first item of the list in *ifap. The list consists of ifaddrs
20 structures, defined as follows:
21 struct ifaddrs {
23 struct ifaddrs *ifa_next; /* Next item in list */
24 char *ifa_name; /* Name of interface */
25 unsigned int ifa_flags; /* Flags from SIOCGIFFLAGS */
26 struct sockaddr *ifa_addr; /* Address of interface */
27 struct sockaddr *ifa_netmask; /* Netmask of interface */
28 union {
29 struct sockaddr *ifu_broadaddr;
30 /* Broadcast address of interface */
31 struct sockaddr *ifu_dstaddr;
32 /* Point-to-point destination address */
33 } ifa_ifu;
34 #define ifa_broadaddr ifa_ifu.ifu_broadaddr
35 #define ifa_dstaddr ifa_ifu.ifu_dstaddr
36 void *ifa_data; /* Address-specific data */
37 };
38 The ifa_next field contains a pointer to the next structure on the
40 list, or NULL if this is the last item of the list.
41 The ifa_name points to the null-terminated interface name.
43 The ifa_flags field contains the interface flags, as returned by the
45 SIOCGIFFLAGS ioctl(2) operation (see netdevice(7) for a list of these
46 flags).
47 The ifa_addr field points to a structure containing the interface ad‐
49 dress. (The sa_family subfield should be consulted to determine the
50 format of the address structure.) This field may contain a null
51 pointer.
52 The ifa_netmask field points to a structure containing the netmask as‐
54 sociated with ifa_addr, if applicable for the address family. This
55 field may contain a null pointer.
56 Depending on whether the bit IFF_BROADCAST or IFF_POINTOPOINT is set in
58 ifa_flags (only one can be set at a time), either ifa_broadaddr will
59 contain the broadcast address associated with ifa_addr (if applicable
60 for the address family) or ifa_dstaddr will contain the destination ad‐
61 dress of the point-to-point interface.
62 The ifa_data field points to a buffer containing address-family-spe‐
64 cific data; this field may be NULL if there is no such data for this
65 interface.
66 The data returned by getifaddrs() is dynamically allocated and should
68 be freed using freeifaddrs() when no longer needed.
69
71 On success, getifaddrs() returns zero; on error, -1 is returned, and
72 errno is set appropriately.
73
75 getifaddrs() may fail and set errno for any of the errors specified for
76 socket(2), bind(2), getsockname(2), recvmsg(2), sendto(2), malloc(3),
77 or realloc(3).
78
80 The getifaddrs() function first appeared in glibc 2.3, but before glibc
81 2.3.3, the implementation supported only IPv4 addresses; IPv6 support
82 was added in glibc 2.3.3. Support of address families other than IPv4
83 is available only on kernels that support netlink.
84
86 For an explanation of the terms used in this section, see at‐
87 tributes(7).
88 ┌────────────────────────────┬───────────────┬─────────┐
90 │Interface │ Attribute │ Value │
91 ├────────────────────────────┼───────────────┼─────────┤
92 │getifaddrs(), freeifaddrs() │ Thread safety │ MT-Safe │
93 └────────────────────────────┴───────────────┴─────────┘
94
96 Not in POSIX.1. This function first appeared in BSDi and is present on
97 the BSD systems, but with slightly different semantics documented—re‐
98 turning one entry per interface, not per address. This means ifa_addr
99 and other fields can actually be NULL if the interface has no address,
100 and no link-level address is returned if the interface has an IP ad‐
101 dress assigned. Also, the way of choosing either ifa_broadaddr or
102 ifa_dstaddr differs on various systems.
103
105 The addresses returned on Linux will usually be the IPv4 and IPv6 ad‐
106 dresses assigned to the interface, but also one AF_PACKET address per
107 interface containing lower-level details about the interface and its
108 physical layer. In this case, the ifa_data field may contain a pointer
109 to a struct rtnl_link_stats, defined in <linux/if_link.h> (in Linux 2.4
110 and earlier, struct net_device_stats, defined in <linux/netdevice.h>),
111 which contains various interface attributes and statistics.
112
114 The program below demonstrates the use of getifaddrs(), freeifaddrs(),
115 and getnameinfo(3). Here is what we see when running this program on
116 one system:
117 $ ./a.out
119 lo AF_PACKET (17)
120 tx_packets = 524; rx_packets = 524
121 tx_bytes = 38788; rx_bytes = 38788
122 wlp3s0 AF_PACKET (17)
123 tx_packets = 108391; rx_packets = 130245
124 tx_bytes = 30420659; rx_bytes = 94230014
125 em1 AF_PACKET (17)
126 tx_packets = 0; rx_packets = 0
127 tx_bytes = 0; rx_bytes = 0
128 lo AF_INET (2)
129 address: <127.0.0.1>
130 wlp3s0 AF_INET (2)
131 address: <192.168.235.137>
132 lo AF_INET6 (10)
133 address: <::1>
134 wlp3s0 AF_INET6 (10)
135 address: <fe80::7ee9:d3ff:fef5:1a91%wlp3s0>
136 Program source
138 #define _GNU_SOURCE /* To get defns of NI_MAXSERV and NI_MAXHOST */
140 #include <arpa/inet.h>
141 #include <sys/socket.h>
142 #include <netdb.h>
143 #include <ifaddrs.h>
144 #include <stdio.h>
145 #include <stdlib.h>
146 #include <unistd.h>
147 #include <linux/if_link.h>
148 int main(int argc, char *argv[])
150 {
151 struct ifaddrs *ifaddr;
152 int family, s;
153 char host[NI_MAXHOST];
154 if (getifaddrs(&ifaddr) == -1) {
156 perror("getifaddrs");
157 exit(EXIT_FAILURE);
158 }
159 /* Walk through linked list, maintaining head pointer so we
161 can free list later */
162 for (struct ifaddrs *ifa = ifaddr; ifa != NULL;
164 ifa = ifa->ifa_next) {
165 if (ifa->ifa_addr == NULL)
166 continue;
167 family = ifa->ifa_addr->sa_family;
169 /* Display interface name and family (including symbolic
171 form of the latter for the common families) */
172 printf("%-8s %s (%d)\n",
174 ifa->ifa_name,
175 (family == AF_PACKET) ? "AF_PACKET" :
176 (family == AF_INET) ? "AF_INET" :
177 (family == AF_INET6) ? "AF_INET6" : "???",
178 family);
179 /* For an AF_INET* interface address, display the address */
181 if (family == AF_INET || family == AF_INET6) {
183 s = getnameinfo(ifa->ifa_addr,
184 (family == AF_INET) ? sizeof(struct sockaddr_in) :
185 sizeof(struct sockaddr_in6),
186 host, NI_MAXHOST,
187 NULL, 0, NI_NUMERICHOST);
188 if (s != 0) {
189 printf("getnameinfo() failed: %s\n", gai_strerror(s));
190 exit(EXIT_FAILURE);
191 }
192 printf("\t\taddress: <%s>\n", host);
194 } else if (family == AF_PACKET && ifa->ifa_data != NULL) {
196 struct rtnl_link_stats *stats = ifa->ifa_data;
197 printf("\t\ttx_packets = %10u; rx_packets = %10u\n"
199 "\t\ttx_bytes = %10u; rx_bytes = %10u\n",
200 stats->tx_packets, stats->rx_packets,
201 stats->tx_bytes, stats->rx_bytes);
202 }
203 }
204 freeifaddrs(ifaddr);
206 exit(EXIT_SUCCESS);
207 }
208
210 bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)
211
213 This page is part of release 5.10 of the Linux man-pages project. A
214 description of the project, information about reporting bugs, and the
215 latest version of this page, can be found at
216 https://www.kernel.org/doc/man-pages/.
217GNU 2020-11-01 GETIFADDRS(3)