X server

That section contains SOME useful information about X servers.

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What does :0.0 mean?

The :0.0 part of the DISPLAY variable denote the display and the screen of an X server.

The display is the first number and equals to a running instance of an X server. If it is using TCP/IP for communication it listens on port 6000 + display-number for connections. With local (UNIX domain sockets) it uses the socket /tmp/.X11-unix/Xdisplay-number

The screen denotes different output devices of the X server. You could start XWin.exe with two -screen options and would end up with two X11 windows. Each of them is a different screen. Other X servers open different screens for different monitors connected to the computer.

Cygwin/X supports different formats of the DISPLAY variable

:0.0 or unix:0.0
This names a local X server and the communication uses the UNIX domain sockets.

hostname:0.0
This names a remote X server and the communication uses the TCP/IP network.

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Xlib: connection to "local_host_name_or_ip_address:0.0" refused by server Xlib: Maximum number of clients reached

Cygwin/X queries getdtablesize () for the maximum number of client connections allowed; by default Cygwin returns 32 from getdtablesize (). Cygwin/X Server Test Series release Test44, released on 2001-08-15, changes the maximum number of clients from 32 to 1024 by passing the square of getdtablesize () to setdtablesize ().