vsock(7) — Linux manual page


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

NAME         top

       vsock - Linux VSOCK address family

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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

       Valid socket types are SOCK_STREAM and SOCK_DGRAM.  SOCK_STREAM
       provides connection-oriented byte streams with guaranteed, in-order
       delivery.  SOCK_DGRAM provides a connectionless datagram packet
       service with best-effort delivery and best-effort ordering.
       Availability of these socket types is dependent on the underlying

       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 destination 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 virtual machine or the host.
       The port number differentiates between multiple services running 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 */
               unsigned char  svm_zero[sizeof(struct sockaddr) -
                                       sizeof(sa_family_t) -
                                       sizeof(unsigned short) -
                                       sizeof(unsigned int) -
                                       sizeof(unsigned int)];

       svm_family is always set to AF_VSOCK.  svm_reserved1 is always set to
       0.  svm_port contains the port number in host byte order.  The port
       numbers below 1024 are called privileged ports.  Only a process with
       the CAP_NET_BIND_SERVICE capability may bind(2) to these port num‐
       bers.  svm_zero must be zero-filled.

       There are several special addresses: VMADDR_CID_ANY (-1U) means any
       address for binding; VMADDR_CID_HYPERVISOR (0) is reserved for ser‐
       vices built into the hypervisor; VMADDR_CID_LOCAL (1) is the well-
       known address for local communication (loopback); VMADDR_CID_HOST (2)
       is the well-known address of the host.

       The special constant VMADDR_PORT_ANY (-1U) means any port number for

   Live migration
       Sockets are affected by live migration of virtual machines.  Con‐
       nected SOCK_STREAM sockets become disconnected when the virtual ma‐
       chine migrates to a new host.  Applications must reconnect when this

       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.

              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.

   Local communication
       VMADDR_CID_LOCAL (1) directs packets to the same host that generated
       them.  This is useful for testing applications on a single host and
       for debugging.

       The local CID obtained with IOCTL_VM_SOCKETS_GET_LOCAL_CID can be
       used for the same purpose, but it is preferable to use VMADDR_CID_LO‐
       CAL .

ERRORS         top

       EACCES Unable to bind to a privileged port without the
              CAP_NET_BIND_SERVICE capability.

              Unable to bind to a port that is already in use.

              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.

              Invalid socket option in setsockopt(2) or getsockopt(2).

              Unable to perform operation on an unconnected socket.

              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.

              Invalid socket protocol number.  The protocol should always be

              Unsupported socket type in socket(2).  Only SOCK_STREAM and
              SOCK_DGRAM are valid.

VERSIONS         top

       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.

       VMADDR_CID_LOCAL is supported since Linux 5.6.  Local communication
       in the guest and on the host is available since Linux 5.6.  Previous
       versions supported only local communication within a guest (not on
       the host), and with only some transports (VMCI and virtio).

SEE ALSO         top

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

COLOPHON         top

       This page is part of release 5.09 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                            2020-02-09                         VSOCK(7)

Pages that refer to this page: socket(2)address_families(7)