1GETIFADDRS(3)              Linux Programmer's Manual             GETIFADDRS(3)
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NAME

6       getifaddrs, freeifaddrs - get interface addresses
7

SYNOPSIS

9       #include <sys/types.h>
10       #include <ifaddrs.h>
11
12       int getifaddrs(struct ifaddrs **ifap);
13       void freeifaddrs(struct ifaddrs *ifa);
14

DESCRIPTION

16       The  getifaddrs() function creates a linked list of structures describ‐
17       ing the network interfaces of the local system, and stores the  address
18       of  the  first item of the list in *ifap.  The list consists of ifaddrs
19       structures, defined as follows:
20
21           struct ifaddrs {
22               struct ifaddrs  *ifa_next;    /* Next item in list */
23               char            *ifa_name;    /* Name of interface */
24               unsigned int     ifa_flags;   /* Flags from SIOCGIFFLAGS */
25               struct sockaddr *ifa_addr;    /* Address of interface */
26               struct sockaddr *ifa_netmask; /* Netmask of interface */
27               union {
28                   struct sockaddr *ifu_broadaddr;
29                                    /* Broadcast address of interface */
30                   struct sockaddr *ifu_dstaddr;
31                                    /* Point-to-point destination address */
32               } ifa_ifu;
33           #define              ifa_broadaddr ifa_ifu.ifu_broadaddr
34           #define              ifa_dstaddr   ifa_ifu.ifu_dstaddr
35               void            *ifa_data;    /* Address-specific data */
36           };
37
38       The ifa_next field contains a pointer to  the  next  structure  on  the
39       list, or NULL if this is the last item of the list.
40
41       The ifa_name points to the null-terminated interface name.
42
43       The  ifa_flags  field  contains the interface flags, as returned by the
44       SIOCGIFFLAGS ioctl(2) operation (see netdevice(7) for a list  of  these
45       flags).
46
47       The  ifa_addr  field points to a structure containing the interface ad‐
48       dress.  (The sa_family subfield should be consulted  to  determine  the
49       format  of  the  address  structure.)   This  field  may contain a null
50       pointer.
51
52       The ifa_netmask field points to a structure containing the netmask  as‐
53       sociated  with  ifa_addr,  if  applicable for the address family.  This
54       field may contain a null pointer.
55
56       Depending on whether the bit IFF_BROADCAST or IFF_POINTOPOINT is set in
57       ifa_flags  (only  one  can be set at a time), either ifa_broadaddr will
58       contain the broadcast address associated with ifa_addr  (if  applicable
59       for the address family) or ifa_dstaddr will contain the destination ad‐
60       dress of the point-to-point interface.
61
62       The ifa_data field points to a  buffer  containing  address-family-spe‐
63       cific  data;  this  field may be NULL if there is no such data for this
64       interface.
65
66       The data returned by getifaddrs() is dynamically allocated  and  should
67       be freed using freeifaddrs() when no longer needed.
68

RETURN VALUE

70       On  success,  getifaddrs()  returns zero; on error, -1 is returned, and
71       errno is set to indicate the error.
72

ERRORS

74       getifaddrs() may fail and set errno for any of the errors specified for
75       socket(2),  bind(2),  getsockname(2), recvmsg(2), sendto(2), malloc(3),
76       or realloc(3).
77

VERSIONS

79       The getifaddrs() function first appeared in glibc 2.3, but before glibc
80       2.3.3,  the  implementation supported only IPv4 addresses; IPv6 support
81       was added in glibc 2.3.3.  Support of address families other than  IPv4
82       is available only on kernels that support netlink.
83

ATTRIBUTES

85       For  an  explanation  of  the  terms  used  in  this  section,  see at‐
86       tributes(7).
87
88       ┌────────────────────────────────────────────┬───────────────┬─────────┐
89Interface                                   Attribute     Value   
90       ├────────────────────────────────────────────┼───────────────┼─────────┤
91getifaddrs(), freeifaddrs()                 │ Thread safety │ MT-Safe │
92       └────────────────────────────────────────────┴───────────────┴─────────┘
93

CONFORMING TO

95       Not in POSIX.1.  This function first appeared in BSDi and is present on
96       the  BSD  systems, but with slightly different semantics documented—re‐
97       turning one entry per interface, not per address.  This means  ifa_addr
98       and  other fields can actually be NULL if the interface has no address,
99       and no link-level address is returned if the interface has  an  IP  ad‐
100       dress  assigned.   Also,  the  way  of choosing either ifa_broadaddr or
101       ifa_dstaddr differs on various systems.
102

NOTES

104       The addresses returned on Linux will usually be the IPv4 and  IPv6  ad‐
105       dresses  assigned  to the interface, but also one AF_PACKET address per
106       interface containing lower-level details about the  interface  and  its
107       physical layer.  In this case, the ifa_data field may contain a pointer
108       to a struct rtnl_link_stats, defined in <linux/if_link.h> (in Linux 2.4
109       and  earlier, struct net_device_stats, defined in <linux/netdevice.h>),
110       which contains various interface attributes and statistics.
111

EXAMPLES

113       The program below demonstrates the use of getifaddrs(),  freeifaddrs(),
114       and  getnameinfo(3).   Here is what we see when running this program on
115       one system:
116
117           $ ./a.out
118           lo       AF_PACKET (17)
119                           tx_packets =        524; rx_packets =        524
120                           tx_bytes   =      38788; rx_bytes   =      38788
121           wlp3s0   AF_PACKET (17)
122                           tx_packets =     108391; rx_packets =     130245
123                           tx_bytes   =   30420659; rx_bytes   =   94230014
124           em1      AF_PACKET (17)
125                           tx_packets =          0; rx_packets =          0
126                           tx_bytes   =          0; rx_bytes   =          0
127           lo       AF_INET (2)
128                           address: <127.0.0.1>
129           wlp3s0   AF_INET (2)
130                           address: <192.168.235.137>
131           lo       AF_INET6 (10)
132                           address: <::1>
133           wlp3s0   AF_INET6 (10)
134                           address: <fe80::7ee9:d3ff:fef5:1a91%wlp3s0>
135
136   Program source
137
138       #define _GNU_SOURCE     /* To get defns of NI_MAXSERV and NI_MAXHOST */
139       #include <arpa/inet.h>
140       #include <sys/socket.h>
141       #include <netdb.h>
142       #include <ifaddrs.h>
143       #include <stdio.h>
144       #include <stdlib.h>
145       #include <unistd.h>
146       #include <linux/if_link.h>
147
148       int main(int argc, char *argv[])
149       {
150           struct ifaddrs *ifaddr;
151           int family, s;
152           char host[NI_MAXHOST];
153
154           if (getifaddrs(&ifaddr) == -1) {
155               perror("getifaddrs");
156               exit(EXIT_FAILURE);
157           }
158
159           /* Walk through linked list, maintaining head pointer so we
160              can free list later. */
161
162           for (struct ifaddrs *ifa = ifaddr; ifa != NULL;
163                    ifa = ifa->ifa_next) {
164               if (ifa->ifa_addr == NULL)
165                   continue;
166
167               family = ifa->ifa_addr->sa_family;
168
169               /* Display interface name and family (including symbolic
170                  form of the latter for the common families). */
171
172               printf("%-8s %s (%d)\n",
173                      ifa->ifa_name,
174                      (family == AF_PACKET) ? "AF_PACKET" :
175                      (family == AF_INET) ? "AF_INET" :
176                      (family == AF_INET6) ? "AF_INET6" : "???",
177                      family);
178
179               /* For an AF_INET* interface address, display the address. */
180
181               if (family == AF_INET || family == AF_INET6) {
182                   s = getnameinfo(ifa->ifa_addr,
183                           (family == AF_INET) ? sizeof(struct sockaddr_in) :
184                                                 sizeof(struct sockaddr_in6),
185                           host, NI_MAXHOST,
186                           NULL, 0, NI_NUMERICHOST);
187                   if (s != 0) {
188                       printf("getnameinfo() failed: %s\n", gai_strerror(s));
189                       exit(EXIT_FAILURE);
190                   }
191
192                   printf("\t\taddress: <%s>\n", host);
193
194               } else if (family == AF_PACKET && ifa->ifa_data != NULL) {
195                   struct rtnl_link_stats *stats = ifa->ifa_data;
196
197                   printf("\t\ttx_packets = %10u; rx_packets = %10u\n"
198                          "\t\ttx_bytes   = %10u; rx_bytes   = %10u\n",
199                          stats->tx_packets, stats->rx_packets,
200                          stats->tx_bytes, stats->rx_bytes);
201               }
202           }
203
204           freeifaddrs(ifaddr);
205           exit(EXIT_SUCCESS);
206       }
207

SEE ALSO

209       bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)
210

COLOPHON

212       This page is part of release 5.13 of the Linux  man-pages  project.   A
213       description  of  the project, information about reporting bugs, and the
214       latest    version    of    this    page,    can     be     found     at
215       https://www.kernel.org/doc/man-pages/.
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219GNU                               2021-03-22                     GETIFADDRS(3)
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