1GETIFADDRS(3)              Linux Programmer's Manual             GETIFADDRS(3)
2
3
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.)
51
52       The  ifa_netmask  field  points  to  a structure containing the netmask
53       associated with ifa_addr, if applicable for the address family.
54
55       Depending on whether the bit IFF_BROADCAST or IFF_POINTOPOINT is set in
56       ifa_flags  (only  one  can be set at a time), either ifa_broadaddr will
57       contain the broadcast address associated with ifa_addr  (if  applicable
58       for  the  address  family)  or ifa_dstaddr will contain the destination
59       address of the point-to-point interface.
60
61       The ifa_data field points to a  buffer  containing  address-family-spe‐
62       cific  data;  this  field may be NULL if there is no such data for this
63       interface.
64
65       The data returned by getifaddrs() is dynamically allocated  and  should
66       be freed using freeifaddrs() when no longer needed.
67

RETURN VALUES

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

ERRORS

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

VERSIONS

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

CONFORMING TO

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

NOTES

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

EXAMPLE

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

SEE ALSO

174       bind(2), getsockname(2), socket(2), packet(7), ifconfig(8)
175

COLOPHON

177       This page is part of release 3.25 of the Linux  man-pages  project.   A
178       description  of  the project, and information about reporting bugs, can
179       be found at http://www.kernel.org/doc/man-pages/.
180
181
182
183GNU                               2009-01-23                     GETIFADDRS(3)
Impressum