Cygwin/X User's Guide
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# Remote sessions via XDMCP

Cygwin/X can be used login to one or several remote sessions using XDMCP (X Display Manager Control Protocol).

Start Cygwin/X with a command similar to the following to login to a single remote session using XDMCP:

`X -query `remote_hostname_or_ip_address``

You may login to several remote sessions with a single or multiple hosts using XDMCP. Each session will need a separate display number, specified by the `:display_number` parameter, such as `:0`. A display number is not the same as a screen number, as a single display can have multiple screens associated with it. Each display listens on a different network port number, so each display can connect to multiple machines. Start Cygwin/X with command lines similar to the following to login to several remote sessions using XDMCP:

`X :0 -query `remote_hostname_or_ip_address_0``

`X :1 -query `remote_hostname_or_ip_address_1``

Note that the `:display_number` parameter is a general X Server parameter, not specific to Cygwin/X. Further documentation of the `:display_number` parameter can be found in the X Server manual page. XDMCP is a complex system that is not specific to Cygwin/X; further discussion of XDMCP is beyond the scope of this document. You may wish to read the Linux XDMCP HOWTO or the X Server XDMCP Options for more information.

> Note: For security reasons, XDMCP is not enabled by default on most modern UNIX distributions. You will have to enable remote logins to your X Display Manager (xdm, kdm, gdm, etc.). See the configuration documentation for your X Display Manager and/or UNIX distribution. The Cygwin/X FAQ section on XDMCP may also be helpful.

> Note: XDMCP suffers from some of the same security problems noted in the previous section, but unfortunately cannot be tunnelled over ssh due to it's use of UDP. A similar effect can be achieved with a command like `ssh -Y `remote_hostname_or_ip_address` Xnest :1 -query localhost`

> Note: In some cases, e.g. if you have multiple network interfaces, it may be necessary to use the `-from `local_ip`` parameter to specify the local IP address to be used.

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