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VSOCK(7) - Linux manual page online | Overview, conventions, and miscellany

Linux VSOCK address family.

VSOCK(7) Linux Programmer's Manual VSOCK(7)


vsock - Linux VSOCK address family


#include <sys/socket.h> #include <linux/vm_sockets.h> stream_socket = socket(AF_VSOCK, SOCK_STREAM, 0); datagram_socket = socket(AF_VSOCK, SOCK_DGRAM, 0);


The VSOCK address family facilitates communication between virtual machines and the host they are running on. This address family is used by guest agents and hypervisor services that need a communications channel that is independent of virtual machine network configu‐ ration. Valid socket types are SOCK_STREAM and SOCK_DGRAM. SOCK_STREAM provides connection-ori‐ ented byte streams with guaranteed, in-order delivery. SOCK_DGRAM provides a connection‐ less datagram packet service with best-effort delivery and best-effort ordering. Avail‐ ability of these socket types is dependent on the underlying hypervisor. A new socket is created with socket(AF_VSOCK, socket_type, 0); When a process wants to establish a connection, it calls connect(2) with a given destina‐ tion socket address. The socket is automatically bound to a free port if unbound. A process can listen for incoming connections by first binding to a socket address using bind(2) and then calling listen(2). Data is transmitted using the send(2) or write(2) families of system calls and data is received using the recv(2) or read(2) families of system calls. Address format A socket address is defined as a combination of a 32-bit Context Identifier (CID) and a 32-bit port number. The CID identifies the source or destination, which is either a vir‐ tual machine or the host. The port number differentiates between multiple services run‐ ning on a single machine. struct sockaddr_vm { sa_family_t svm_family; /* Address family: AF_VSOCK */ unsigned short svm_reserved1; unsigned int svm_port; /* Port # in host byte order */ unsigned int svm_cid; /* Address in host byte order */ }; svm_family is always set to AF_VSOCK. svm_reserved1 is always set to 0. svm_port con‐ tains the port number in host byte order. The port numbers below 1024 are called privi‐ leged ports. Only a process with the CAP_NET_BIND_SERVICE capability may bind(2) to these port numbers. There are several special addresses: VMADDR_CID_ANY (-1U) means any address for binding; VMADDR_CID_HYPERVISOR (0) is reserved for services built into the hypervisor; VMADDR_CID_RESERVED (1) must not be used; VMADDR_CID_HOST (2) is the well-known address of the host. The special constant VMADDR_PORT_ANY (-1U) means any port number for binding. Live migration Sockets are affected by live migration of virtual machines. Connected SOCK_STREAM sockets become disconnected when the virtual machine migrates to a new host. Applications must reconnect when this happens. The local CID may change across live migration if the old CID is not available on the new host. Bound sockets are automatically updated to the new CID. Ioctls IOCTL_VM_SOCKETS_GET_LOCAL_CID Get the CID of the local machine. The argument is a pointer to an unsigned int. ioctl(socket, IOCTL_VM_SOCKETS_GET_LOCAL_CID, &cid); Consider using VMADDR_CID_ANY when binding instead of getting the local CID with IOCTL_VM_SOCKETS_GET_LOCAL_CID.


EACCES Unable to bind to a privileged port without the CAP_NET_BIND_SERVICE capability. EADDRINUSE Unable to bind to a port that is already in use. EADDRNOTAVAIL Unable to find a free port for binding or unable to bind to a nonlocal CID. EINVAL Invalid parameters. This includes: attempting to bind a socket that is already bound, providing an invalid struct sockaddr_vm, and other input validation errors. ENOPROTOOPT Invalid socket option in setsockopt(2) or getsockopt(2). ENOTCONN Unable to perform operation on an unconnected socket. EOPNOTSUPP Operation not supported. This includes: the MSG_OOB flag that is not implemented for the send(2) family of syscalls and MSG_PEEK for the recv(2) family of syscalls. EPROTONOSUPPORT Invalid socket protocol number. The protocol should always be 0. ESOCKTNOSUPPORT Unsupported socket type in socket(2). Only SOCK_STREAM and SOCK_DGRAM are valid.


Support for VMware (VMCI) has been available since Linux 3.9. KVM (virtio) is supported since Linux 4.8. Hyper-V is supported since Linux 4.14.


bind(2), connect(2), listen(2), recv(2), send(2), socket(2), capabilities(7)


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
Linux 2017-11-30 VSOCK(7)
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vsock(7) referred by
refer to bind(2) | capabilities(7) | connect(2) | getsockopt(2) | listen(2) | read(2) | recv(2) | send(2) | socket(2) | write(2)
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