Client connections to Virtuoso servers running on the same Unix or Linux server host can benefit from faster connections utilizing Unix Domain Sockets. This does not apply to Windows platforms.

By default Virtuoso will open a Unix Domain listen socket in addition to the TCP listen socket. The name of the UD socket will be:

/tmp/virt-<tcp-listen-port>

When a client attempts to connect to the Virtuoso server using the specific address localhost it will first try connecting to the UD socket, failing that it will silently revert to the TCP socket.

Unix Domain Socket connections only work if localhost is explicitly specified or the host is unspecified which defaults to a localhost connection. UD socket connections will not work to any other address such as:

virt.mydomain.com:1111
127.0.0.1:1111

regardless of whether that is the localhost or not.

Unix Domain sockets can be disabled using the DisableUnixSocket parameter in the Parameters section of the Virtuoso INI file.

The sys_connected_server_address() function can be used to check the connection type. It will return

/tmp/virt-<tcp-listen-port>

for connections using UD sockets.