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Linux kernel and C library user-space interface documentation


Manual pages about using a GNU/Linux system


address_families - socket address families (domains)


#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
int socket(int domain, int type, int protocol);


The domain argument of the socket(2) specifies a communication domain; this selects the protocol family which will be used for communication. These families are defined in <sys/socket.h>. The formats currently understood by the Linux kernel include:
Local communication For further information, see unix(7).
IPv4 Internet protocols. For further information, see ip(7).
Amateur radio AX.25 protocol. For further information, see ax25(4).
AF_IPX IPX - Novell protocols.
AppleTalk For further information, see ddp(7).
AX.25 packet layer protocol. For further information, see netrom(4), The Packet Radio Protocols and Linux and the AX.25, NET/ROM, and ROSE network programming chapters of the Linux Amateur Radio AX.25 HOWTO
Can’t be used for creating sockets; mostly used for bridge links in rtnetlink(7) protocol commands.
Access to raw ATM Permanent Virtual Circuits (PVCs). For further information, see the ATM on Linux HOWTO
AF_X25 ITU-T X.25 / ISO-8208 protocol. For further information, see x25(7).
IPv6 Internet protocols. For further information, see ipv6(7).
RATS (Radio Amateur Telecommunications Society) Open Systems environment (ROSE) AX.25 packet layer protocol. For further information, see the resources listed for AF_NETROM.
DECet protocol sockets. See Documentation/networking/decnet.txt in the Linux kernel source tree for details.
Reserved for "802.2LLC project"; never used.
This was a short-lived (between Linux 2.1.30 and 2.1.99pre2) protocol family for firewall upcalls.
AF_KEY Key management protocol, originally developed for usage with IPsec (since Linux 2.1.38). This has no relation to keyctl(2) and the in-kernel key storage facility. See RFC 2367 PF_KEY Key Management API, Version 2 for details.
Kernel user interface device For further information, see netlink(7).
Low-level packet interface. For further information, see packet(7).
Acorn Econet protocol (removed in Linux 3.5). See the Econet documentation for details.
Access to ATM Switched Virtual Circuits (SVCs) See the ATM on Linux HOWTO for details.
AF_RDS Reliable Datagram Sockets (RDS) protocol (since Linux 2.6.30). RDS over RDMA has no relation to AF_SMC or AF_XDP. For further information see rds(7), rds-rdma(7), and Documentation/networking/rds.txt in the Linux kernel source tree.
Socket interface over IrDA (moved to staging in Linux 4.14, removed in Linux 4.17). For further information see irda(7).
Generic PPP transport layer, for setting up L2 tunnels (L2TP and PPPoE). See Documentation/networking/l2tp.txt in the Linux kernel source tree for details.
Legacy protocol for wide area network (WAN) connectivity that was used by Sangoma WAN cards (called "WANPIPE"); removed in Linux 2.6.21.
AF_LLC Logical link control (IEEE 802.2 LLC) protocol, upper part of data link layer of ISO/OSI networking protocol stack (since Linux 2.4); has no relation to AF_PACKET. See chapter 13.5.3. Logical Link Control in Understanding Linux Kernel Internals (O’Reilly Media, 2006) and IEEE Standards for Local Area Networks: Logical Link Control (The Institute of Electronics and Electronics Engineers, Inc., New York, New York, 1985) for details. See also some historical notes regarding its development.
AF_IB InfiniBand native addressing (since Linux 3.11).
Multiprotocol Label Switching (since Linux 4.1); mostly used for configuring MPLS routing via netlink(7), as it doesn’t expose ability to create sockets to user space.
AF_CAN Controller Area Network automotive bus protocol (since Linux 2.6.25). See Documentation/networking/can.rst in the Linux kernel source tree for details.
TIPC, "cluster domain sockets" protocol (since Linux 2.6.16). See TIPC Programmer’s Guide and the protocol description for details.
Bluetooth low-level socket protocol (since Linux 3.11). See Bluetooth Management API overview and An Introduction to Bluetooth Programming by Albert Huang for details.
IUCV (inter-user communication vehicle) z/VM protocol for hypervisor-guest interaction (since Linux 2.6.21); has no relation to AF_VSOCK and/or AF_SMC See IUCV protocol overview for details.
Rx, Andrew File System remote procedure call protocol (since Linux 2.6.22). See Documentation/networking/rxrpc.txt in the Linux kernel source tree for details.
New "modular ISDN" driver interface protocol (since Linux 2.6.27). See the mISDN wiki for details.
Nokia cellular modem IPC/RPC interface (since Linux 2.6.31). See Documentation/networking/phonet.txt in the Linux kernel source tree for details.
IEEE 802.15.4 WPAN (wireless personal area network) raw packet protocol (since Linux 2.6.31). See Documentation/networking/ieee802154.txt in the Linux kernel source tree for details.
Ericsson’s Communication CPU to Application CPU interface (CAIF) protocol (since Linux 2.6.36). See Documentation/networking/caif/Linux-CAIF.txt in the Linux kernel source tree for details.
AF_ALG Interface to kernel crypto API (since Linux 2.6.38). See Documentation/crypto/userspace-if.rst in the Linux kernel source tree for details.
VMWare VSockets protocol for hypervisor-guest interaction (since Linux 3.9); has no relation to AF_IUCV and AF_SMC. For further information, see vsock(7).
AF_KCM KCM (kernel connection multiplexor) interface (since Linux 4.6). See Documentation/networking/kcm.txt in the Linux kernel source tree for details.
Qualcomm IPC router interface protocol (since Linux 4.7).
AF_SMC SMC-R (shared memory communications over RDMA) protocol (since Linux 4.11), and SMC-D (shared memory communications, direct memory access) protocol for intra-node z/VM quest interaction (since Linux 4.19); has no relation to AF_RDS, AF_IUCV or AF_VSOCK. See RFC 7609 IBM’s Shared Memory Communications over RDMA (SMC-R) Protocol for details regarding SMC-R. See SMC-D Reference Information for details regarding SMC-D.
AF_XDP XDP (express data path) interface (since Linux 4.18). See Documentation/networking/af_xdp.rst in the Linux kernel source tree for details.


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