1GETIFADDRS(3)              Linux Programmer's Manual             GETIFADDRS(3)
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4

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
14       void freeifaddrs(struct ifaddrs *ifa);
15

DESCRIPTION

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
22           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
39       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
42       The ifa_name points to the null-terminated interface name.
43
44       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
48       The  ifa_addr  field  points  to  a  structure containing the interface
49       address.  (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
53       The ifa_netmask field points to  a  structure  containing  the  netmask
54       associated  with  ifa_addr, if applicable for the address family.  This
55       field may contain a NULL pointer.
56
57       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
61       address of the point-to-point interface.
62
63       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
67       The data returned by getifaddrs() is dynamically allocated  and  should
68       be freed using freeifaddrs() when no longer needed.
69

RETURN VALUE

71       On  success,  getifaddrs()  returns zero; on error, -1 is returned, and
72       errno is set appropriately.
73

ERRORS

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

VERSIONS

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

CONFORMING TO

86       Not  in  POSIX.1-2001.   This  function  first  appeared in BSDi and is
87       present on the BSD systems, but with slightly different semantics docu‐
88       mented—returning  one entry per interface, not per address.  This means
89       ifa_addr and other fields can actually be NULL if the interface has  no
90       address,  and no link-level address is returned if the interface has an
91       IP address assigned.  Also, the way of choosing either ifa_broadaddr or
92       ifa_dstaddr differs on various systems.
93

NOTES

95       The  addresses  returned  on  Linux  will  usually be the IPv4 and IPv6
96       addresses assigned to the interface, but also one AF_PACKET address per
97       interface  containing  lower-level  details about the interface and its
98       physical layer.  In this case, the ifa_data field may contain a pointer
99       to a struct rtnl_link_stats, defined in <linux/if_link.h> (in Linux 2.4
100       and earlier, struct net_device_stats, defined in  <linux/netdevice.h>),
101       which contains various interface attributes and statistics.
102

EXAMPLE

104       The  program below demonstrates the use of getifaddrs(), freeifaddrs(),
105       and getnameinfo(3).  Here is what we see when running this  program  on
106       one system:
107
108           $ ./a.out
109           lo      address family: 17 (AF_PACKET)
110           eth0    address family: 17 (AF_PACKET)
111           lo      address family: 2 (AF_INET)
112                   address: <127.0.0.1>
113           eth0    address family: 2 (AF_INET)
114                   address: <10.1.1.4>
115           lo      address family: 10 (AF_INET6)
116                   address: <::1>
117           eth0    address family: 10 (AF_INET6)
118                   address: <fe80::2d0:59ff:feda:eb51%eth0>
119
120   Program source
121
122       #include <arpa/inet.h>
123       #include <sys/socket.h>
124       #include <netdb.h>
125       #include <ifaddrs.h>
126       #include <stdio.h>
127       #include <stdlib.h>
128       #include <unistd.h>
129
130       int
131       main(int argc, char *argv[])
132       {
133           struct ifaddrs *ifaddr, *ifa;
134           int family, s;
135           char host[NI_MAXHOST];
136
137           if (getifaddrs(&ifaddr) == -1) {
138               perror("getifaddrs");
139               exit(EXIT_FAILURE);
140           }
141
142           /* Walk through linked list, maintaining head pointer so we
143              can free list later */
144
145           for (ifa = ifaddr; ifa != NULL; ifa = ifa->ifa_next) {
146               if (ifa->ifa_addr == NULL)
147                   continue;
148
149               family = ifa->ifa_addr->sa_family;
150
151               /* Display interface name and family (including symbolic
152                  form of the latter for the common families) */
153
154               printf("%s  address family: %d%s\n",
155                       ifa->ifa_name, family,
156                       (family == AF_PACKET) ? " (AF_PACKET)" :
157                       (family == AF_INET) ?   " (AF_INET)" :
158                       (family == AF_INET6) ?  " (AF_INET6)" : "");
159
160               /* For an AF_INET* interface address, display the address */
161
162               if (family == AF_INET || family == AF_INET6) {
163                   s = getnameinfo(ifa->ifa_addr,
164                           (family == AF_INET) ? sizeof(struct sockaddr_in) :
165                                                 sizeof(struct sockaddr_in6),
166                           host, NI_MAXHOST, NULL, 0, NI_NUMERICHOST);
167                   if (s != 0) {
168                       printf("getnameinfo() failed: %s\n", gai_strerror(s));
169                       exit(EXIT_FAILURE);
170                   }
171                   printf("\taddress: <%s>\n", host);
172               }
173           }
174
175           freeifaddrs(ifaddr);
176           exit(EXIT_SUCCESS);
177       }
178

SEE ALSO

180       bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)
181

COLOPHON

183       This  page  is  part of release 3.53 of the Linux man-pages project.  A
184       description of the project, and information about reporting  bugs,  can
185       be found at http://www.kernel.org/doc/man-pages/.
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189GNU                               2012-11-11                     GETIFADDRS(3)
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