pcap_findalldevs(3PCAP) man page

Updated: 9 August 2024 • View in plain text • Return to Main Contents

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pcap_findalldevs, pcap_freealldevs - get a list of capture devices, and free that list

#include <pcap/pcap.h>

char errbuf[PCAP_ERRBUF_SIZE];

int pcap_findalldevs(pcap_if_t **alldevsp, char *errbuf);
void pcap_freealldevs(pcap_if_t *alldevs);

pcap_findalldevs() constructs a list of network devices that can be opened with pcap_create(3PCAP) and pcap_activate(3PCAP) or with pcap_open_live(3PCAP). (Note that there may be network devices that cannot be opened by the process calling pcap_findalldevs(), because, for example, that process does not have sufficient privileges to open them for capturing; if so, those devices will not appear on the list.) alldevsp is a pointer to a pcap_if_t *; errbuf is a buffer large enough to hold at least PCAP_ERRBUF_SIZE chars.

If pcap_findalldevs() succeeds, the pointer pointed to by alldevsp is set to point to the first element of the list, or to NULL if no devices were found (this is considered success). Each element of the list is of type pcap_if_t, and has the following members:

next

if not NULL, a pointer to the next element in the list; NULL for the last element of the list

name

a pointer to a string giving a name for the device to pass to pcap_open_live()

description

if not NULL, a pointer to a string giving a human-readable description of the device

addresses

a pointer to the first element of a list of network addresses for the device, or NULL if the device has no addresses

flags

device flags:

PCAP_IF_LOOPBACK

set if the device is a loopback interface

PCAP_IF_UP

set if the device is up

PCAP_IF_RUNNING

set if the device is running

PCAP_IF_WIRELESS

set if the device is a wireless interface; this includes IrDA as well as radio-based networks such as IEEE 802.15.4 and IEEE 802.11, so it doesn't just mean Wi-Fi

PCAP_IF_CONNECTION_STATUS

a bitmask for an indication of whether the adapter is connected or not; for wireless interfaces, "connected" means "associated with a network"

The possible values for the connection status bits are:

PCAP_IF_CONNECTION_STATUS_UNKNOWN

it's unknown whether the adapter is connected or not

PCAP_IF_CONNECTION_STATUS_CONNECTED

the adapter is connected

PCAP_IF_CONNECTION_STATUS_DISCONNECTED

the adapter is disconnected

PCAP_IF_CONNECTION_STATUS_NOT_APPLICABLE

the notion of "connected" and "disconnected" don't apply to this interface; for example, it doesn't apply to a loopback device

Each element of the list of addresses is of type pcap_addr_t, and has the following members:

next

if not NULL, a pointer to the next element in the list; NULL for the last element of the list

addr

a pointer to a struct sockaddr containing an address

netmask

if not NULL, a pointer to a struct sockaddr that contains the netmask corresponding to the address pointed to by addr

broadaddr

if not NULL, a pointer to a struct sockaddr that contains the broadcast address corresponding to the address pointed to by addr; may be NULL if the device doesn't support broadcasts

dstaddr

if not NULL, a pointer to a struct sockaddr that contains the destination address corresponding to the address pointed to by addr; may be NULL if the device isn't a point-to-point interface

Note that the addresses in the list of addresses might be IPv4 addresses, IPv6 addresses, or some other type of addresses, so you must check the sa_family member of the struct sockaddr before interpreting the contents of the address; do not assume that the addresses are all IPv4 addresses, or even all IPv4 or IPv6 addresses. IPv4 addresses have the value AF_INET, IPv6 addresses have the value AF_INET6 (which older operating systems that don't support IPv6 might not define), and other addresses have other values. Whether other addresses are returned, and what types they might have is platform-dependent. Namely, link-layer addresses, such as Ethernet MAC addresses, have the value AF_PACKET (on Linux) or AF_LINK (on AIX, FreeBSD, Haiku, illumos, macOS, NetBSD and OpenBSD) or are not returned at all (on GNU/Hurd and Solaris).

For IPv4 addresses, the struct sockaddr pointer can be interpreted as if it pointed to a struct sockaddr_in; for IPv6 addresses, it can be interpreted as if it pointed to a struct sockaddr_in6. For link-layer addresses, it can be interpreted as if it pointed to a struct sockaddr_ll (for AF_PACKET) or a struct sockaddr_dl (for AF_LINK).

The list of devices must be freed with pcap_freealldevs(3PCAP), which frees the list pointed to by alldevs.

pcap_findalldevs() returns 0 on success and PCAP_ERROR on failure; as indicated, finding no devices is considered success, rather than failure, so 0 will be returned in that case. If PCAP_ERROR is returned, errbuf is filled in with an appropriate error message, and the pointer pointed to by alldevsp is set to NULL.

The PCAP_IF_UP and PCAP_IF_RUNNING constants became available in libpcap release 1.6.1. The PCAP_IF_WIRELESS, PCAP_IF_CONNECTION_STATUS, PCAP_IF_CONNECTION_STATUS_UNKNOWN, PCAP_IF_CONNECTION_STATUS_CONNECTED, PCAP_IF_CONNECTION_STATUS_DISCONNECTED, and PCAP_IF_CONNECTION_STATUS_NOT_APPLICABLE constants became available in libpcap release 1.9.0.

pcap(3PCAP)

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