HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. |  |
NAME |LIBRARY |SYNOPSIS |DESCRIPTION |RETURN VALUE |ERRORS |ATTRIBUTES |STANDARDS |HISTORY |NOTES |EXAMPLES |SEE ALSO |COLOPHON | |
getifaddrs(3) Library Functions Manualgetifaddrs(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);
Thegetifaddrs() 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 ofifaddrs 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 */ }; Theifa_next field contains a pointer to the next structure on the list, or NULL if this is the last item of the list. Theifa_name points to the null-terminated interface name. Theifa_flags field contains the interface flags, as returned by theSIOCGIFFLAGS ioctl(2) operation (seenetdevice(7) for a list of these flags). Theifa_addr field points to a structure containing the interface address. (Thesa_family subfield should be consulted to determine the format of the address structure.) This field may contain a null pointer. Theifa_netmask field points to a structure containing the netmask associated withifa_addr, if applicable for the address family. This field may contain a null pointer. Depending on whether the bitIFF_BROADCASTorIFF_POINTOPOINTis set inifa_flags (only one can be set at a time), eitherifa_broadaddr will contain the broadcast address associated withifa_addr (if applicable for the address family) orifa_dstaddr will contain the destination address of the point-to-point interface. Theifa_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 bygetifaddrs() is dynamically allocated and should be freed usingfreeifaddrs() when no longer needed.On success,getifaddrs() returns zero; on error, -1 is returned, anderrno is set to indicate the error.
getifaddrs() may fail and seterrno for any of the errors specified forsocket(2),bind(2),getsockname(2),recvmsg(2),sendto(2),malloc(3), orrealloc(3).
For an explanation of the terms used in this section, seeattributes(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 meansifa_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 eitherifa_broadaddr orifa_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 oneAF_PACKET address per interface containing lower-level details about the interface and its physical layer. In this case, theifa_data field may contain a pointer to astruct rtnl_link_stats, defined in<linux/if_link.h> (in Linux 2.4 and earlier,structnet_device_stats, defined in<linux/netdevice.h>), which contains various interface attributes and statistics.
The program below demonstrates the use ofgetifaddrs(),freeifaddrs(), andgetnameinfo(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 theman-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-6.15.tar.gz fetched from ⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on 2025-08-11. 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 isnot part of the original manual page), send a mail to man-pages@man7.orgLinux man-pages 6.15 2025-05-17getifaddrs(3)Pages that refer to this page:bind(2), getsockname(2), if_nameindex(3), if_nametoindex(3)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |