if_nametoindex man page

if_nametoindex, if_indextoname — mappings between network interface names and indexes


#include <net/if.h>

unsigned int if_nametoindex(const char *ifname);

char *if_indextoname(unsigned int ifindex, char *ifname);


The if_nametoindex() function returns the index of the network interface corresponding to the name ifname.

The if_indextoname() function returns the name of the network interface corresponding to the interface index ifindex. The name is placed in the buffer pointed to by ifname. The buffer must allow for the storage of at least IF_NAMESIZE bytes.

Return Value

On success, if_nametoindex() returns the index number of the network interface; on error, 0 is returned and errno is set appropriately.

On success, if_indextoname() returns ifname; on error, NULL is returned and errno is set appropriately.


if_nametoindex() may fail and set errno if:


No interface found with given name.

if_indextoname() may fail and set errno if:


No interface found for the index.

if_nametoindex() and if_indextoname() may also fail for any of the errors specified for socket(2) or ioctl(2).


For an explanation of the terms used in this section, see attributes(7).

Interface Attribute Value
if_nametoindex(), if_indextoname() Thread safety MT-Safe

Conforming to

POSIX.1-2001, POSIX.1-2008, RFC 3493.

This function first appeared in BSDi.

See Also

getifaddrs(3), if_nameindex(3), ifconfig(8)


This page is part of release 4.15 of the Linux man-pages project. A description of the project, information about reporting bugs, and the latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Referenced By

dhcpcd(8), dhcpcd.conf(5), if_nameindex(3).

The man page if_indextoname(3) is an alias of if_nametoindex(3).

2017-09-15 GNU Linux Programmer's Manual