nxproxy - Man Page

NX Proxy Tool


nxproxy [<options>] <host>:<port>


nxproxy is a tool that allows one to tunnel X sessions through the NX compression library. nxproxy is a backend application utilized by various client application (Remmina, X2Go Client, PyHoca-Gui, Arctica Client, TheQVD Client, etc.).

Command Line Options


Specify that nxproxy has to run on the 'X client' side, listening for connections and impersonating an X server.


Specify that nxproxy has to run in 'X server' mode, thus forwarding the connections to daemons running on the client.


Print this message.


Print version information.

-d <int>

Set log level (0 for FATAL, 1 for ERROR, 2 for WARNING, 3 for INFO, 4 for DEBUG). The default is 0.

-o <string>

Name of the log file. Default is stderr.

-f <string>

Specify log format. The characters in <string> define how the loglines are formatted. The following characters are supported, default is '0':


only the plain text without any additions. This is the default.


include time


include loglevel


include thread ids


include the location of the log call in the source code


Put at the end, specifies the host and port of the listening proxy.

Nx/Nx Display Options

Multiple nx/nx options can be specified in the DISPLAY environment or on the command line, by using the nx/nx,option=value notation.


An indication of the link speed that is going to be used between the proxies. Usually the compression and the other link parameters depend on this setting. The value can be either 'modem', 'isdn', 'adsl', 'wan', 'lan', 'local' or a bandwidth specification, like for example '56k', '1m', '100m', etc.


Type of session, for example 'windows', 'unix-kde'. 'unix-application', etc.


Specify the real display where X connections have to be forwarded by the proxy running on the client.


Local port used for accepting the proxy connection.


Bind to the loopback device only.


Name or IP of host that can connect to the proxy.


Name or IP of host that the proxy will connect to.


Remote port used for the connection.


Number of connection attempts.


The root directory for the session. Usually is the C-* or S-* in the .nx directory in the user's home, with '*' being the virtual display.


Name of the session file. The default is the name 'session' in the session directory.


Name of the log file used by the proxy. The default is the name 'errors' in the session directory.


Name of the file where are written the proxy statistics. The default is a file 'stats' in the session directory. The proxy replaces the data in the file whenever it receives a SIGUSR1 or SIGUSR2 signal:

SIGUSR1: Gives total statistics, i.e. statistics collected since the beginning of the session.

SIGUSR2: Gives partial statistics, i.e. statistics collected since the last time this signal was received.


Use the provided cookie for authenticating to the remote proxy. The same cookie is used as the fake value used for the X authorization. The fake cookie is replaced on the X server side with the real cookie to be used for the display, so that the real cookie doesn't have to travel over the net. When not using a proxy cookie, any host will be able to connect to the proxy. See also the 'accept' parameter.


A boolean indicating if TCP_NODELAY has to be set on the proxy link. Old Linux kernels had problems with handling TCP_NODELAY on PPP links.


Let or not the agent decide when it is the best time to flush the proxy link. If set to 0, the proxy will flush any encoded data immediately. The option has only effect on the X client side proxy.


Enable or disable use of the RENDER extension.


Try to suppress trivial sources of X roundtrips by generating the reply on the X client side.


Enable X differential compression.


Enable or disable the ZLIB data compression. It is possible to specify a value between 0 and 9. Usually the value is chosen automatically based on the requested link setting.


Enable or disable the ZLIB stream compression. The value, between 0 and 9, is usually determined according to the requested link setting. Not fully implemented in nx-X11 Agent, yet.


Specify a bitrate limit allowed for this session.


Trigger memory optimizations used to keep small the size of X buffers. This is useful on embedded plat- forms, or where memory is scarce.


Size of the in-memory X message cache. Setting the value to 0 will disable the memory cache as well as the NX differential compression.


Size of the persistent image cache.


Enable the use of the MIT-SHM extension between the nxproxy and the real X server. A value greater than 1 is assumed to be the size of requested shared memory segment. By default, the size of the segment is determined based on the size of the in-memory cache.


Enable loading a persistent X message cache at the proxy startup.


Enable saving a persistent X message cache at the end of session.


Enable or disable forwarding of CUPS connections, by listening on the optional port 'n'.


Enable or disable forwarding of the auxiliary X channel used for controlling the keyboard. The 'keybd=<int>' form is accepted for backward compatibility.


Enable or disable forwarding of SMB connections. The 'samba=<int>' form is accepted for backward compatibility.


Enable forwarding of audio connections.


Enable forwarding of HTTP connections.


Enable forwarding of reversed connections to a font server running on the NX server.


Enable forwarding of file transfer connections.


Determine the distribution of channel ids between the proxies. By default, channels whose ids are multiple of 8 (starting from 0) are reserved for the NX client side. All the other channels can be allocated by the nx-X11 Agent side.


Specify the keep-alive timeout used by proxies to determine if there is a network problem preventing communication with the remote peer. A value of 0 disables the check.


Specify the number of seconds the proxy has to wait at session shutdown before closing all channels. The feature is used by the NX server to ensure that services are disconnected before shutting down the link.


Determine the method used to compress images.


The product id of the client or server. The value is ignored by the proxy, but the client or server can provide it to facilitate the support.


Enable production of core dumps when aborting the proxy connection.


Specify an additional file containing options that has to be merged with option read from the command line or the environment.


Add the given process to the list of daemons that must be terminated at session shutdown. Multiple 'kill=<int>' options can be specified. The proxy will send them a SIGTERM signal just before exiting.


Optimize for responsiveness, rather than for the best use of all the available bandwidth.


Should be set to 1 if the proxy is running as part of a program providing encryption of the point to point communication.

The following options are interpreted by the nx-NX Agent. They are ignored by the proxy:


NX Environment Variables

The nxproxy application (and also nxagent when using nxcomp support) can be influenced by the following environment variables:


The root NX directory is the place where the session directory and the cache files are created. This is usually overridden by passing the 'root=' option. By default, the root NX directory is assumed to be the directory '.nx' in the user's home.


The directory where NX programs and libraries reside. If not set, the value is assumed to be '/usr/NX'. Programs, libraries and data files are respectedly searched in the 'bin', 'lib' and 'share' subdirectories.


The NX user's home directory. If NX_ROOT is not set or invalid, the user's NX directory is created here.


The directory where all temporary files are to be created.


The full path to the <nxclient> executable. If the variable is not set, the <nxclient> executable will be run assuming that the program is in the system path. This can be useful on platforms like Windows and the MacOS X where <nxclient> is located in a different directory compared to the other programs, to make easier for the user to execute the program from the shell.


The full path to the slave channel handler. When the slave channel is enabled, the agent will listen on a port and forward the connection to the NX_SLAVE_CMD program. This can be used to implement agent/proxy communication for applications such as serial port and USB forwarding.

Shell Environment Variables


The variable is checked in the case NX_HOME is not set, null or invalid.


The variable is checked whenever the NX_TEMP directory is not set, null or invalid.


The path where all executables are searched, except <nxclient>. If NX_CLIENT is not set, also the client executable is searched in the system path.


System-wide library search order. This should be set by the program invoking the proxy.


On the X server side, the DISPLAY variable indicates the location of the X11 server. When nxcomp is used as a transport library, the DISPLAY may represent a NX transport specification and options can passed in the form nx/nx,option=value...


This is the file containing the X11 authorization cookie. If not set, the file is assumed to be in the user's home (either NX_HOME or HOME).


The nxproxy application has originally been derived from a software project called DXCP. The company NoMachine turned DXCP into nxcomp with nxproxy as executable around nxcomp.

The current maintenance of nxproxy (major version 3) is coordinated between various projects, mainly by The Arctica Project, TheQVD (Qindel Group) and the X2Go Project.

This manual has been written by Mike Gabriel <mike.gabriel@das-netzwerkteam.de> for the X2Go project (http://www.x2go.org) and later on improved for the Arctica Project (https://arctica-project.org).


Jun 2023 Version NX Proxy