Access control

Only use Xming option -ac or 'xhost +' on trusted networks, never on public ones i.e. be careful as they grant access to everyone. The X protocol network traffic is only encrypted if using X-Forwarding with SSH and this is therefore the recommended method for access control, all others method are potentially unsafe (e.g. using xhost or xauth with telnet).

• X-Forwarding

  If you use X-Forwarding then you don't need to directly use 'xhost'/'xauth' or set a $DISPLAY variable. Use PuTTY with SSH and X-Forwarding and enable it in the 'sshd' daemon (sshd_config file) on the remote machine

  X11Forwarding yes
  X11DisplayOffset 10
  X11UseLocalhost yes
  

  My typical PuTTY settings

  
  Use PuTTY to get a remote terminal on your Windows desktop and from that run the X clients you need, or run X clients via 'plink' using a stored session or a 'user@hostname' command. On that remote terminal, $DISPLAY is automatically set to point at display 10 or above when X-forwarding

  $ echo $DISPLAY
  localhost:10.0
  

  Both XLaunch and Xmingrc make starting an X Client via Xming's plink easy.

  Note: If you are connecting to an Ubuntu Server Edition you need package 'xauth' installed for X-Forwarding to work. Also use 'pam_xauth' to automatically forward 'xauth' cookies between users when using 'su'.

• xhost program

  To use the X server access control program, 'xhost' (host-based), from 'Command Prompt' e.g. on Windows machine '192.168.0.2', with remote machine '192.168.0.3', using display-number '0'...

  >set DISPLAY=localhost:0    or 127.0.0.1:0 or 192.168.0.2:0
  >Xming :0 -multiwindow -clipboard
  >xeyes    or whatever locally, will display on the Windows desktop
  >xhost +192.168.0.3
    and then on the remote machine
  $ export DISPLAY=192.168.0.2:0
  $ xeyes   or whatever remotely, will display on the Windows desktop

  Running 'xhost' without any arguments shows the current hosts allowed to access the server. 'xhost' can be used to give (or deny) systems access to the server interactively, overriding the contents of Xn.hosts files.

• Xn.hosts files

  An X server uses a host-based access control list for deciding whether or not to accept connections from clients on a particular machine. This list initially consists of the host on which the X server is running as well as any remote machines listed in the file Xn.hosts, where n is the display-number of the X server. Each line of the file should contain a remote hostname with no leading or trailing spaces and the file should reside in the Xming install directory.

  The Xming installer provides a 'X0.hosts' file containing one line

  localhost

• xauth program

  The Xming magic cookie program, 'xauth' (user-based), uses an 'Xauthority' file (not the traditional '.Xauthority' file) in the %HOME% directory, from 'Command Prompt' e.g. on Windows machine '192.168.0.2' with user 'colin'...

  >set DISPLAY=192.168.0.2:0
  >set HOME=%USERPROFILE%
  >Xming :0 -multiwindow -clipboard
  >xeyes    or whatever locally, will display on the Windows desktop
  >xauth generate :0 .
  xauth:  creating new authority file C:\Documents and Settings\colin/Xauthority
  >xauth list
  192.168.0.2:0  MIT-MAGIC-COOKIE-1  7aa7cd57c47f90cec40e6c534537a075   (Example 32 char hex cookie!)
    restart the Xming X server with the cookie authorization
  >Xming :0 -auth "C:/Documents and Settings/colin/Xauthority" -multiwindow -clipboard
    then copy the newly created 'Xauthority' file to /tmp/ on the remote machine
    and then on the remote machine
  $ xauth merge /tmp/Xauthority
  $ export DISPLAY=192.168.0.2:0
  $ xeyes   or whatever remotely, will display on the Windows desktop

Environment Variables

The following Windows Environment Variables are created or used by the server


Where 'path-to-Xming.exe' is the location of the Xming executable, typically 'C:\Program Files\Xming'.

If you run 'keychain' for key management with SSH you additionally get variables SSH_AUTH_SOCK and SSH_AGENT_PID. If the latter is detected by XLaunch (Run Remote/Use SSH), it runs without an 'Command Prompt' console as an interactive password entry should not be needed.

Files and Locations

The following files and locations are used by Xming, often in a way different from X on Linux/Unix

font-dirs is supplied containing...

# font-dirs
# comma-separated list of directories to add to the default font path
# defaults are built-ins, misc, TTF, Type1, 75dpi, 100dpi
# also allows entries on individual lines
C:\Program Files\Xming\fonts\dejavu,C:\Program Files\Xming\fonts\cyrillic
C:\WINDOWS\Fonts

Xdefaults is supplied containing...

#ifdef COLOR
*customization: -color
#endif

X0.hosts is supplied containing...

localhost

The following files may be in a directory other than the Xming install directory

Keyboards

Xming keyboard data originates from the X Keyboard Configuration Database Project.
The current list of keyboard models, layouts and variants is here.

If the keyboard doesn't work for your locale please email the part of the Xming log that looks something like

(--) winConfigKeyboard - Layout: "00000424" (00000424)
(EE) Keyboardlayout "Slovenian" (00000424) is unknown

so that the entry can be added to the known keyboard layouts.

Also try using 'setxkbmap', when Xming is running, if you have the wrong language variant

>setxkbmap ch -variant fr
equivalent to starting Xming
>Xming :0 -multiwindow -clipboard -xkblayout ch -xkbvariant fr

Zone Alarm can cause Xming to freeze right after startup, fix by removing it.

NumLock

Some Unix flavours cannot have NumLock enabled when running Xming. Disable NumLock with remote AIX, SUN Solaris and HPUX, if keys or mouse buttons are not working, using numlockoff. The numlockoff zip file (MD5 signature 902155aa2599917dfa37fa9378f31568) contains the code and executable to check the state of the NumLock key and synthesize a keydown/keyup sequence of the NumLock key if it's down.

AIX

The X Keyboard Extension doesn't work with AIX. The X Keyboard Extension is enabled by default, so you must disable it with the -kb parameter.

For recent AIX systems this tip has been superseded by...
AIX logs in using '/usr/dt/config/Xsetup' (used only if using 'dtlogin' as the XDMCP client) and '/usr/dt/bin/Xsession' (used when logging in to CDE). These contain a call to 'xmodmap' (for IBM keyboards) which makes the Xming keyboard go wrong whether you're using XKB or not. Commenting out these two calls allows you to use Xming with XKB enabled on AIX.
Note that the AIX X server has the XKB extension, but it is disabled by default in favour of 'xmodmap' methods.

Mouse

If you use the Logitech Mouse Drivers uncheck the option 'Disable Acceleration In Games' or your mouse will be slow in Xming.
Logitech web-cam drivers can also cause 'Can't open display' problems.

Multiplemonitors

Screens cannot be positioned on anything other than the first monitor with FullScreen Shadow DirectDraw (-engine 2), but are OK in Shadow GDI (-engine 1)...

Xming -screen 0 @2 -fullscreen -multiplemonitors            renders incorrectly on the first monitor
Xming -screen 0 @2 -multiplemonitors                        renders correctly on the second monitor
Xming -screen 0 @2 -fullscreen -multiplemonitors -engine 1  renders correctly on the second monitor

Following on from the original patch for multiple monitors it appears that FullScreen DirectDraw can only draw on the 'Windows Primary Display' irrespective of the use of SM_CXVIRTUALSCREEN etc in the code.

Network

Failure reports

• winClipboardIOErrorHandler!
• winClipboardProc - setjmp returned: X exiting
• winClipboardProc - setjmp returned for IO Error Handler.
• winMultiWindowXMsgProcIOErrorHandler!
• winInitMultiWindowXMsgProc - setjmp returned: X. Exiting.
• winInitMultiWindowXMsgProc - Caught IO Error. Exiting.
• winMultiWindowWMIOErrorHandler!
• winInitMultiWindowWM - setjmp returned: X. Exiting.
• winInitMultiWindowWM - Caught IO Error. Exiting.

any of these indicate network failure with the X protocol. Maybe due to the presence of firewalls, or high latency.

Performance

SSH compression may be of some help on slower networks, but will slow things down on fast networks.

The encoding of network traffic used by the X protocol is optimised for LANs, where the time spent encoding and decoding the data is more important than minimizing the amount of data transmitted. While this is fine for an Ethernet, it becomes a problem for very slow networks like serial lines. X.Org have abandoned LBX, their own built-in compression system, in favour of using SSH compression on slow networks.

Operation via a personal firewall, VPN or any software that modifies the TCP/IP stack, will increase latency. Especially Webwasher, Symantec Antivirus and Zone Alarm. Disabling these products isn't sufficient, uninstall them to restore network performance with the X protocol.

OpenGL

If OpenGL doesn't work with a program then you can switch on various diagnostic output. Start Xming with special environment variables set


For example

>set GLWIN_ENABLE_DEBUG=1
>set GLWIN_DUMP_PFD=1
>Xming :0 -multiwindow -clipboard

or try the alternative Mesa renderer instead. Also a difficult client will usually work if a version of Mesa is installed on the remote Linux/Unix machine to pre-empt server-side rendering.

Windows versions

Xming code, installers and binaries are tested, by me, only on 32-bit Windows XP, 2003 Server and Vista. I've had positive reports of Xming in WoW64 on 64-bit Windows.

Windows 2000 is no longer supported, these were the last compatible installers...

Last Windows 2000 Release	Version	State	Released	MD5 signature	Size MB
Xming Xming-mesa	6.9.0.18	Obsolete	09 Oct 2006	d0b655030e400aee5242d8db6b624047 8b016b6ee4ea6c4f2565097bcd85d6bb	2.06 2.47
Xming-fonts	6.9.0.6	Obsolete	25 Jun 2006	e0cd413af96345e95da1b9d524c63763	30.0

Windows performance

If you insist on running the whole of KDE or Gnome in -multiwindow or -fullscreen mode then don't expect blistering performance. Use coLinux or XDMCP mode if you want a full Linux/Unix graphical environment on the Windows desktop.

Some people find running Xming with +bs -wm (the backing store) improves the performance of image updates, e.g. with Firefox, but I haven't tested this.

Extensions, pseudocolor and bell

Xming doesn't support the MIT-SHM, XFree86-Bigfont or XVideo extensions. MIT-SHM only applies to local X clients anyway so adding it would not improve network performance. However some technologies, like VirtualGL, could benefit by Xming having MIT-SHM (watch this space).

Xinerama is depreciated and not available in Xming. Future work will favour XRandR.

Xming also does not yet have a working -pseudocolor mode, for 8-bit colour use -fullscreen -depth 8 in one window mode which enables DirectDraw (-engine 2).

The bell (feep) is not controllable by -f or 'xset b' options. Xming just uses the Windows 'MessageBeep()' function for the bell.

XDMCP

First read the notes in XLaunch for XDMCP remote settings.

• If you have a multiple interfaced (i.e. multihomed) Windows machine you may need to use the -from option to set the correct source address (in IP address dotted format). This should not be necessary in recent versions.
• For security, Xming XDMCP mode is constrained to work only on local networks and it is not recommended to attempt to use it through routers or firewalls. You can use Xnest running XDMCP through X-Forwarding to get a secure connection to the Xming server. e.g. from a X-Forwarding PuTTY terminal...

  $ Xnest :1 -query localhost -geometry 1024x768+50+25 -fp tcp/localhost:7100

  but don't expect Xnest to be as fast as a 'direct' XDMCP session.
• Some distributions default X Display Manager config files start X with the -nolisten tcp option, or similar, which prevents remote connections.
• If you connect via XDMCP to a system that uses gdm, and have a problem with the clipboard, you should add (or modify) this section in the gdm.conf file (or /etc/gdm/custom.conf)

  [daemon]
  KillInitClients=false

  and then restart gdm with gdm-restart. Also some X Display Managers do not work well anyway with the Xming clipboard. So just try using standard 'xdm' as an alternative.
• If you get 100% CPU use with Xming.exe, the chances are XDMCP can't establish a socket connection with the remote machine.

Table of Contents

1. Access control
   1. X-Forwarding
   2. xhost program
   3. Xn.hosts files
   4. xauth program
2. Environment Variables
3. Files and Locations
4. Keyboards
   1. NumLock
   2. AIX
5. Mouse
6. Multiplemonitors
7. Network
   1. Failure reports
   2. Performance
8. OpenGL
9. Windows versions
10. Windows performance
11. Extensions, pseudocolor and bell
12. XDMCP

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Creative Commons Attribution-NonCommercial-ShareAlike 2.0 UK: England & Wales License.
Copyright © 2005-2008 Colin Harrison Some rights reserved