Cygwin/X Frequently Asked
Questions2023-02-18 18:22
Questions and Answers
1. General Information
1.1. What is Cygwin/X?
Cygwin/X is a port of the X Window System to Cygwin. Cygwin provides a UNIX-like API on the
Win32 platform.
1.2. What is Cygwin?
Cygwin tools are, in the words of the Cygwin FAQ (http://cygwin.com/faq.html#faq.what), “ portsof the popular GNU development tools and utilities for Microsoft Windows. They run thanks to the
Cygwin library which provides the POSIX system calls and environment these programs expect. ”
Cygwin provides the compiler (gcc), libraries, headers, and other utilities which build and support
the operation of Cygwin/X.
1.3. What is the X Window System?
[ScheiflerGettys92]
The X Window System, or X, is a network-transparent window system. With X, multiple
applications can run simultaneously in windows, generating text and graphics in monochrome orcolor on a bitmap display. Network transparency means that application programs can run onmachines scattered through the network.
1.4. What is an X Server?
An X Server is a program that provides display and user input services to other programs. In
comparison, a file server provides other programs with access to file storage devices. File servers
are typically located in a remote location and you use the services of a file server from the machinethat you are located at. In contrast, an X Server is typically running on the machine that you arelocated at; display and user input services may be requested by programs running on yourmachine, as well as by programs running on remote machines.
1.5. What is an X client?
An X client is a program that utilizes the display and user input services provided by an X Server.
X clients may run on the same or disparate machine as the X Server that is providing display anduser input services.

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Cygwin/X Frequently Asked Questions
1.6. What does DISPLAY=:0.0 mean?
The DISPLAY environment variable instructs an X client which X server it is to connect to bydefault. Typically this can be overriden by running the client with a -display or -d commandline option.
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 should equal the display number given to a running instance ofan X server. By default the X server uses display number 0. If the X server is using TCP/IP for
communication it listens on port 6000 + display-number for X client connections. For 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 X 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.
See the DISPLAY NAMES section of man X for more information.

1.7. Why port the X Window System to Microsoft Windows?
Porting X Window System to Microsoft Windows benefits many people and projects in many ways:•

Prior to Cygwin/X only commercial, closed source X Servers were available for Microsoft
Windows.

•

An X Server on Windows may be used to display the output of programs running on remote
UNIX machines.

•

Cygwin/X, in conjunction with Cygwin, provides a complete compatibility layer for compilingand running UNIX applications on Microsoft Windows.

1.8. Is there a Cygwin/X newsgroup?
No, Cygwin/X does not have a newsgroup; however, we do have a mailing list. See Q: 1.9.
You can read and post to the mailing list using your newsreader using the GMANE(http://gmane.org/find.php?list=os.cygwin) mail-to-news gateway.

1.9. Is there a Cygwin/X mailing list?
Yes, Cygwin/X is on-topic for the cygwin@cygwin.com mailing list. Non-subscribers may post to
this list. Visit the Cygwin Mailing Lists (https://cygwin.com/lists.html) page to subscribe to
cygwin@cygwin.com as well as to read and search an online archive of the mailing list traffic.

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Cygwin/X Frequently Asked Questions
2. Installation
2.1. What versions of Windows does Cygwin/X run on?
Cygwin/X aims to support all versions of Windows supported by Cygwin.
However, Cygwin/X is not tested on older versions of Windows (i.e. Windows NT4, Windows
2000) and may be broken. Problem reports are welcomed.
Cygwin/X requires Cygwin to compile and run. Cygwin is not, as of writing, available on
Microsoft Windows CE, therefore Cygwin/X is not currently available on Microsoft Windows CE.

2.2. How is Cygwin/X installed?
The Cygwin/X User’s Guide (http://x.cygwin.com/docs/ug/cygwin-x-ug.html) thoroughly
documents the installation process. Installation is performed through Cygwin’s setup program.
2.3. Fatal server error: Can’t read lock file /tmp/.X0-lockThis question should be obsolete.
A1: /tmp resides on a FAT filesystem
Start the server with the -nolock option. See Q: 4.2.
You should really consider updating the filesystem to NTFS using Microsoft’s convert.exe tool.

A2: /tmp resides on a NTFS filesystem.
This can be caused by a stale lock file being left behind after the X server is run by a user with
Adminstrator rights, which cannot be overwritten when the X server is next run by a user without
Adminstrator rights.
Failure to clean up the lock file properly is a bug in the X server, but until that is fixed thefollowing workarounds may be neccessary.
1. Try removing the stale lock file using rm -f /tmp/.Xn-lock where n is the display number. If
this fails due to insufficent permissions, you must either get the owner or a user with
Adminstrator rights to remove the stale lock file.
2. Try starting the server with the -nolock option. (See Q: 4.2.)
Technical details: The X server attempts to create a lock file in /tmp by creating the file under atemporary name, then renaming it to the proper name (by hard linking it under the correct name,then unlinking it from the temporary name). If this rename fails it attempts to read the existing lock
file to determine the pid of an already running server. The FAT filesystem does not support
hardlinks so this operation cannot succeed. On NFTS filesystems, the failure case appears to bethat lock file was created successfully, but the rename failed due to a stale lock file created by auser with Adminstrator rights.

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Cygwin/X Frequently Asked Questions
2.4. Nothing appears to happen when I try to start the X server using the "XWin Server" startmenu shortcut.
A1:
This answer should be obsolete.
Task manager shows the startxwin.exe process starting, spawning XWin.exe and xterm.exe, but
no windows are shown. Running startxwin.exe from a bash shell works correctly. This is causedby having tty in the CYGWIN environment variable set through the Windows control panel.
Removing tty resolves this issue.
If you really need CYGWIN=tty for working with cmd.exe windows, you’ll have to arrange to setthat by some other means before invoking cygwin.bat.

A2:
Try running startxwin from a bash shell in the mintty terminal emulator, it should output someerror message which should indicate why it’s not able to start.
Note: For technical reasons, the output of XWin doesn’t appear in cmd.exe windows unlessthe CYGWIN environment variable set through the Windows control panel contains tty , so toensure the output can be seen, use mintty.

3. Upgrade3.1. What happened to my X server? Where did /usr/X11R6/ go?
The upgrade from X.Org R6.8 to modular X.Org R7.4 made a lot of changes. Please read theannounce email (http://cygwin.com/ml/cygwin-xfree-announce/2008-11/msg00000.html) and pay
attention to the upgrade instructions
3.2. I upgraded my X server and now I can’t type anything into any X application
This question should be obsolete.
Launch the X server via the shortcut under "Cygwin-X" on the start menu.
Technical details: The startxwin.bat script used to set several enviroment variables used by the X
server to specify the location of files it needs to access. Specifically this batch file would set
XKEYSYMDB to /usr/X11R6/lib/X11/XKeysymDB. This file was moved to/usr/share/X11/XKeysymDB. The keyboard won’t work if XKEYSYMDB points to a non-existent
file.
If you are (perhaps unintentionally) using a copy of the old startxwin.bat (perhaps under anothername) to start the X server, remove the environment variables XAPPLRESDIR, XCMSDB, XNLSPATH
and XKEYSYMDB from it, or (preferrably) use the updated startxwin.
If echo $XKEYSYMDB outputs something, you have something else setting XKEYSYMDB in yourenvironment. Find it and remove it.

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Cygwin/X Frequently Asked Questions
These variables were always being set to the defaults, so they can simply be removed. See Q: 8.8.
for the reason why you might need to set them.

3.3. I can’t find startxwin.bat or startxwin.exe to start the X server
The executable startxwin.exe previously used to start the X server has been retired and replacedwith a shell script startxwin.
The MS-DOS batch file startxwin.bat previously used to start the X server has been retired, as
implementing this as a batch file made it difficult to reliably wait until the the X server had started
before starting any clients.
X.Org now uses the prefix /usr not /usr/X11R6. So startxwin.bat was moved from/usr/X11R6/bin/startxwin.bat to /usr/bin/startxwin.bat.
A "XWin Server" shortcut to startxwin is created on the Start menu, under "Cygwin-X"
startxwin and the Start menu link to it are now installed by the xinit package.

3.4. Moved question
3.5. My favourite font has gone! The font Emacs uses is just boxes
Only minimal fonts will be installed after the upgrade from X.Org R6.8 to modular X.Org.
Font packages are now named font-<author/class>-<fonttype>
Some packages dependencies have not yet been updated for the fonts they require, so you may
need to manually install the needed fonts. For example, to provide the font emacs wants to use bydefault you will probably want to install font-adobe-dpi75 (or font-adobe-dpi100 if you
like large fonts). This package provides the courier , helvetica, new century schoolbook
and times font families.
The lucida font family is provided by the package font-bh-dpi75 (or font-bh-dpi100). The
monospaced version, lucida typewriter is provided by the package
font-bh-lucidatypewriter-dpi75 (or font-bh-lucidatypewriter-dpi100).
Note that after installing fonts you will need to restart the X server or run xset fp default; xset fp
rehash to make the new fonts available

3.6. Where has xhost/xlsfonts/etc. gone?
Previously all the X utility programs were contained in a single package, xorg-x11-bin, which
needed to be updated when any of the programs it contained was updated. In modular X each ofthese programs can be found in a separate package, usually named xhost/xlsfont/etc.
3.7. How do I get rid of that menu at the top of my xterm?
Run it as xterm +tb, or add XTerm*toolBar: false to ~/.Xresources5

Cygwin/X Frequently Asked Questions
3.8. ssh -X now says "Warning: untrusted X11 forwarding setup failed: xauth key data notgenerated"
See Q: 6.1. and following. See point 3 in this mail(http://cygwin.com/ml/cygwin-xfree/2008-11/msg00154.html). Use ssh -Y.
Technical details: ssh tried to run xauth generate to create a untrusted cookie for the session,
which failed because the server isn’t compiled with the XCSECURITY extension built-in. Since
OpenSSH 7.2p1, ssh does not fallback to trusted forwarding, so no X11 forwarding is setup.

3.9. nedit fails to start with an error message
This question should be obsolete.
$ nedit
X Error of failed request: BadMatch (invalid parameter attributes)
Major opcode of failed request: 70 (X_PolyFillRectangle)
Serial number of failed request: some number
Current serial number in output stream: some other number

nedit needs rebuilding with a patch to work around an issue lesstif has with current X servers.
Until this happemns, you can work around the issue by adding XLIB_SKIP_ARGB_VISUALS toyour enviroment, e.g.
$ export XLIB_SKIP_ARGB_VISUALS=1$ nedit3.10. I start my X server with startx or xinit and now all my X windows are contained within one
large root Windows window? How do I get it back to each X window in it’s own Windows
window?
This is a deliberate change from Cygwin/X X11 R6.9 behaviour.
1. Start the X server using the "XWin Server" shortcut under "Cygwin-X" on the Start menu, or
using startxwin.
Note: If you wish to customize the X clients started when the X server starts, you can do sousing a ~/.startxwinrc script.
2. Alternatively, add the server option -multiwindow to your xinit or startx invocation, i.e.
xinit -- -multiwindow or startx -- -multiwindow
3. Alternatively, put XWin -multiwindow into ~/.xserverrc or/etc/X11/xinit/xserverrc

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3.11. Moved question
3.12. I upgraded and now X exits immediately after starting
Since xinit-1.3.4-1, startxwin is now implemented by a script based on startx. Unfortunately,
this has changed the behaviour in a backwards-incompatible way, as the X server is now killed
when ~/.startxwinrc exits.
If you have an empty ~/.startxwinrc, you should change it to contain exec sleep infinity so the
X server will not exit until explicitly told to do so.
If you are using a custom ~/.startxwinrc, either run the last client in the foreground (i.e.
without &), so the X server exits when that client exits, or use exec sleep infinity as describedabove.
You should also make sure that ~/.startxwinrc is executable (e.g. chmod +x ~/.startxwinrc).
See the announce mail (https://cygwin.com/ml/cygwin-xfree-announce/2014-11/msg00004.html)
for more details.

3.13. I upgraded and now X clients can’t connect
A1:
Since X server 1.17, by default the server does not listen for TCP/IP connections, only accepting
local connections on a unix domain socket.
For local clients, use DISPLAY=:0.0, rather than DISPLAY=localhost:0.0,
DISPLAY=127.0.0.1:0.0, DISPLAY=::1:0.0, etc. See Q: 1.6..

A2:
For remote clients, rather than connecting over TCP/IP by explicitly setting DISPLAY and allowing
access using xhost or by disabling access control, use ssh tunnelling with ssh -Y instead. (See theUser’s Guide section on X forwarding using ssh(http://x.cygwin.com/docs/ug/using-remote-apps.html#using-remote-apps-ssh) for more details).

A3:
Use the -listen tcp option to restore the previous behaviour, allowing the X server to open a
TCP/IP socket as well e.g. startxwin -- -listen tcp. See Q: 4.2..
4. Configuration
4.1. Is there an xorg.conf or XF86Config file?
No. Options which are configurable are available as command line options. For example, for more
information on configuring other keyboard layouts using command line options, see Q: 5.1.1.

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4.2. What are the command line options for X? How do I add command line options for X?
The Cygwin/X User’s Guide (http://x.cygwin.com/docs/ug/cygwin-x-ug.html) and man XWin
(http://x.cygwin.com/docs/man1/XWin.1.html) document the command line options for X.
To supply a command line option to X:• If you use the start menu shortcut to start the X server, you will need to amend it’s target to add
an option, e.g. C:\cygwin\bin\run.exe --quote /usr/bin/bash.exe -l -c "/usr/bin/startxwin --nolock"Note: Note well that the entire command after -c is quoted

Note: Note that this start menu shortcut is created by the xinit package, and your changes
will be overwritten when the xinit package is updated.

Note: Note that X server options to startxwin are preceded by --.

••If you use startxwin, xinit or startx to start the server, run it as e.g. startxwin -- -nolock, xinit-- -nolock or startx -- -nolock
If you use startxwin.bat or startxwin.sh to start the server, add e.g. -nolock to the
XWin line in that script.

4.3. Why does X ignore the display depth that I pass on the command line?
When running in windowed mode or GDI-based fullscreen mode, X must run the X Server atwhatever display depth Windows is currently using; in these cases the display depth passed on thecommand line is ignored. X only uses the display depth parameter when running in a
DirectDraw-based fullscreen mode, as DirectDraw allows applications to change the display
resolution and depth when running in fullscreen mode.
4.4. I have a two button mouse, can I emulate a three button mouse?
Yes. Pass the -emulate3buttons timeout_in_milliseconds parameter to X, where
timeout_in_milliseconds is the, optional, maximum number of milliseconds between abutton release and opposite button press that will trigger an emulated third button press.
4.5. Is there a Focus-Follows-Mouse feature (Auto-Focus)?
This is a setting of the window manager used. The default window manager twm has no suchfeature. But with fvwm2 this can be achieved with the this configuration entry:
Focus FocusFollowsMouse

Other window managers (eg. windowmaker) have similar features too.

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Cygwin/X Frequently Asked Questions
If you are using the -multiwindow mode you can not set this behaviour in the window manager
but you can use the TweakUI tool to enable this feature for all windows, not limited to Cygwin/X
windows.

4.6. The option -nounixkill has no effect. How can i prevent the server shutdown an
Ctrl-Alt-BackSpace?
This question should be obsolete as the TerminateServer keybinding is no longer present bydefault.
The TerminateServer keybinding can be enabled with
setxkbmap -option terminate:ctrl_alt_bksp

4.7. I have a multihead system. Do I need special options to make it work? I have a multihead
system. Why are my X-application windows white?
You should start X with the -multiplemonitors option.
Note that this option is enabled by default in -multiwindow mode.

4.8. I have a firewall. Is there anything I have to take care of?
X uses port 6000/TCP when the option -listen tcp is used. You will have to allow incoming
and outgoing traffic on this port even if you are only using local clients. X has a builtin access
control so you won’t have to worry about opening the port. If you are still concerned about
security, you may limit the allowed hosts to the local IP addresses.

If you use a different display number check section Q: 1.6. for details about which ports are used.
For additional information about firewalls and XDMCP connections check Q: 7.3..
5. Internationalization
5.1. Keyboard support
5.1.1. How do I use a non-U.S. keyboard layout?
Some keyboard layouts are autodetected from the Windows keyboard settings. For theselayouts no special change is needed. For all other layouts there is the possibility to configure
the layout via commandline options.
The main option for changing the layout is -xkblayout countrycode wherecountrycode is in most cases the 2 character code which also represents the country ininternet adresses (e.g. Australia = au, Deutschland = de, France = fr, Japan = jp)
Other options for tweaking the XKB layout are -xkbmodel,-xkbvariant, -xkboptions
and -xkbrules. These are the counterparts for the similar named options known from thexorg.conf file.

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If the loading fails, check Q: 5.1.6.

5.1.2. Is there a way to add a layout to the list of autodetected layouts?
If your keyboard layout is not automatically detected you can send the required information
for including it into Cygwin/X to cygwin@cygwin.com. Please include the following
information in your mail:•The windows keyboard layout code and the layout name
You will find it in /var/log/xwin/XWin.0.log in lines similar to these:(--) winConfigKeyboard - Layout: "00001809" (00001809)(EE) Keyboardlayout "Irish" (00001809) is unknown•

The XKB layout code for this layout if you know it. Please experiment with setxkbmap or-xkblayout (as described in Q: 5.1.1.) to find an XKB layout code which works for you,otherwise the maintainers will have to guess it.

•

A description how the layout looks like. This makes it easy to identify the matching XKBlayout code. Many layouts are available from the Microsoft Global Dev(http://www.microsoft.com/globaldev/reference/keyboards.mspx) website (It seems thatwebsite only works with some browsers). Just add a link to your layout.

5.1.3. Where can I find an xmodmap for my non-U.S. keyboard layout?
This question should be obsolete The package xkeyboard-config should contain justabout any needed layout
Or, you can use xkeycaps to automatically generate a modmap for one of over 208 different
layouts. See the xkeycaps home page (http://www.jwz.org/xkeycaps/) to download and formore information.
5.1.4. How do I get my non-U.S. keyboard modmap to be installed when using xdmcp?
See Q: 5.1.1.
5.1.5. Logging into AIX via XDMCP causes the keyboard to function as if AltGr ispermanently pressed.
[paraphrased from the Xming FAQ(http://www.straightrunning.com/XmingNotes/trouble.php)] AIX login scripts contain a call
to xmodmap (for IBM keyboards) which causes the keyboard to be incorrectly configured for
XWin. Commenting out those calls should allow you to use XWin with AIX.
The XKB extension is now always enabled in the X.Org xserver, so the previous answer tothis question of disabling the XKB extension with the -kb parameter is no longer applicable.

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5.1.6. Loading an XKB keyboard layout selected with -xkblayout fails
Not all keyboard layouts are tested very well and some contain errors or do not work at all.
To test if the compiling of your layout works start
setxkbmap de -print | xkbcomp -w3 -xkm - :0.0

(replace the "de" with your layout code). This may produce warnings, but must not produce
errors. If there are errors then please report them to the mailing list.
5.1.7. I have Windows XP with Powertoys installed and AltGr does not work. What can I do?
This question should be obsolete.
5.1.8. AltGr does not work properly when connecting to various older commercial unices(e.g. HP-UX, AIX) or to old XFree86.
xkeyboard-config XKB keyboard layouts generally have AltGr mapped as

ISO_Level3_Shift to access additional characters on non-english keyboards. For reasons
unknown to us, this is incompatible with some older X11 releases. We don’t have access tosuch a machine, so we are unable to track this down and find a reason.
It has been reported that sometimes it helps to run
DISPLAY=:0.0 setxkbmap languagecodefrom a cygwin shell after connecting.
See this mailing list thread (http://cygwin.com/ml/cygwin-xfree/2011-07/msg00011.html)
for more discussion and a possible workaround.
5.2. Display problems
5.2.1. How do I get bash to display accents and/or umlauts?
(Heinz Peter Hippenstiel) Add the following lines to .inputrc in your Cygwin home
directory (e.g. ~/.inputrc):
set input-meta on# to accept 8-bit charactersset output-meta on# to show 8-bit charactersset convert-meta off # to show it as character, not the octal representation

5.2.2. How do I put bash into “8 bit” mode?
See Q: 5.2.1.
5.2.3. How do I display unicode characters in an xterm?
A1: for Cygwin 1.7
If you have a UTF-8 locale configured, this should all just work :-).
To confirm this is working properly, you may try the following:11

Cygwin/X Frequently Asked Questions$ wget http://www.cl.cam.ac.uk/~mgk25/ucs/examples/quickbrown.txt[...]$ cat quickbrown.txt$ wget http://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-demo.txt[...]$ cat UTF-8-demo.txt

If you want to be able type unicode characters into this xterm, you’ll need to configure yourbash shell not to escape 8-bit characters, see Q: 5.2.1.

A2: for Cygwin 1.5
Start your xterm in UTF-8 mode as xterm +lc -u8.
To confirm this is working properly, you may try the following$ wget http://www.cl.cam.ac.uk/~mgk25/ucs/examples/quickbrown.txt[...]$ cat quickbrown.txt

For reasons I don’t currently understand, the default fixed font is only capable of supplying
accented roman, hiragana and katakana characters, so if you wish to work with e.g. greek,
cyrillic, hebrew, thai, etc. you’ll need to start your xterm specifying a suitable font e.g. xterm+lc -u8 -fn -misc-fixed-medium-r-semicondensed--13-120-75-75-c-60-iso10646-1
To confirm this is working properly, you may try the following$ wget http://www.cl.cam.ac.uk/~mgk25/ucs/examples/UTF-8-demo.txt[...]$ cat UTF-8-demo.txt

For other programs run from your xterm to output properly (e.g. less, which is why cat isused in the examples above), you may also need to set the LANG environment variable to
LL_CC .UTF-8, where LL_CC is your language and country code.
If you want to be able type unicode characters into this xterm, you’ll need to configure yourbash shell not to escape 8-bit characters, see Q: 5.2.1.
See also the main Cygwin FAQ question on unicode support in Cygwin(http://cygwin.com/faq/faq.html#faq.using.unicode)
6. Remote connections
6.1. X11Forwarding does not work with OpenSSH under Cygwin
A1:
Try adding the -v option to ssh, which often pinpoints the reason for a connection problem.
From the ssh man-page : -v Verbose mode. Causes ssh to print debugging messages about its
progress. This is helpful in debugging connection, authentication, and configuration problems.
Multiple -v options increase the verbosity. The maximum is 3.

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A2:
Before establishing the ssh connection the xserver must be started and the environment variable
DISPLAY must be set.
$ DISPLAY=:0.0$ export DISPLAY$ ssh -Y remotehostor$ DISPLAY=:0.0 ssh -Y remotehost

A3:
Make sure you’re not starting ssh with the option -X . Since OpenSSH 7.2p1, ssh does not fallback
to trusted forwarding, option -Y , so no X11 forwarding is setup. Use ssh -Y.
Make sure you’re not starting ssh with the option -x (lowercase). This disables X11 forwarding.

A4:
Check that X11Forwarding is not disabled in the ssh client configuration.
The configfiles are by default ~/.ssh/config and /etc/ssh_config. The file in the home
directory overrides settings in the global one.
The configfile is split into various sections starting with “Host wildcard ”. The section applies toall hosts where wildcard matches the hostname.
If this section contains an entry “ForwardX11 no” then X11Forwarding is disabled. To enable itchange the entry to:
ForwardX11 yes

A5:
Check that X11Forwarding is not disabled in the ssh server configuration.
The configfile is by default /etc/ssh/sshd_config. If there is an entry “X11Forwarding no”
then X11Forwarding is disabled.
If you have write access to the config file then change it to
X11Forwarding yes

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The OpenSSH server must be restarted or SIGHUP’ed to re-read the configuration file after it ischanged. Otherwise, ask your administrator to change this for you.

A6:
[Frederick W. Wheeler] If the remote machine is a Windows machine using Cygwin OpenSSH
server, make sure the Cygwin xauth package is installed on the remote machine. The OpenSSH
server needs to be able to run xauth to do X11 Forwarding.

6.2. Why do remote programs crash with an X Error of failed request: BadAtom? Why do remote
programs exit when you try to copy and paste?
This question should be obsolete since the SECURITY extension is now disabled
OpenSSH 3.8 enables untrusted X11Forwarding by default when connecting to an ssh server that
supports it.
You will quickly notice that this is the case if most of your X applications are now killed when you
try to copy and paste, X applications fail with an error similar to that below, or if xdpyinfo returns
only a fraction of the supported extensions that it does if run locally.
X Error of failed request: BadAtom (invalid Atom parameter)
Major opcode of failed request: 18 (X_ChangeProperty)
Atom id in failed request: 0x114
Serial number of failed request: 370
Current serial number in output stream: 372

It is easiest to just override untrusted X11Forwarding by passing -Y to ssh in place of -X . The -Y
does the same thing as -X , but it enables trusted X11 forwarding for the current connection.
Setting “ForwardX11Trusted yes” in the ssh client configuration file does the same thing. See man
ssh_config for more information.
See also Q: 6.1.

6.3. I’m confused about the difference between trusted and untrusted X11 forwarding. What does
"Warning: untrusted X11 forwarding setup failed: xauth key data not generated" mean? Why is the
SECURITY extension disabled?
The warning means that ssh is going to use trusted X11 forwarding because untrusted X11
forwarding depends on the SECURITY extension, which isn’t built into the X server and has been
disabled by default upstream.
Trusted X11 forwarding means that you trust the server that you wish to ssh into. The X server willallow remote clients to do whatever a local client would be able to do to your X session, forexample, monitor your keypresses and take a screenshot. Such programs could be run by amalicious or compromised root user on the ssh server, or under your account if it wascompromised on the ssh server.

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Cygwin/X Frequently Asked Questions
Starting with OpenSSH 3.8, untrusted forwarding is the default when X forwarding is requested
using the -X command line option and you need to use the option -Y or specify“ForwardX11Trusted yes” in the client configuration for trusted forwarding by default.
Since OpenSSH 7.2p1, untrusted forwarding (ssh -X ) does not fallback to ssh -Y trusted
forwarding.
So why is this disabled? Untrusted X11 forwarding was meant to be a way to allow logins to
unknown or insecure systems. It generates a cookie with xauth and uses the security extension tolimit what the remote client is allowed to do. But this is widely considered to be not useful,because the security extension uses an arbitrary and limited access control policy, which results ina lot of applications not working correctly (e.g. not being able to cut and paste) and what is really afalse sense of security. See this mail for more on the subject(http://cygwin.com/ml/cygwin-xfree/2008-11/msg00154.html).
(Words adapted from an email by Yaakov Selkowitz)

6.4. What does "Warning: no xauth data; using fake authentication data for X11 forwarding"mean?
Unless you started the X server with the -auth option (typically by using startx) this warning is
expected and can safely be ignored.
6.5. Why can’t new remote X clients connect to the X server after 20 minutes?
Starting with OpenSSH 5.6, ssh enforces the ForwardX11Timeout (which defaults to 1200
seconds) when an untrusted connections is requested, even if an untrusted connection could not bemade (e.g. you used ssh -X which asks for an untrusted connection, and got the "untrusted X11
forwarding setup failed" warning). This means that no new connections to the X server can bemade 20 minutes after the ssh connection is established.
Use ssh -Y. See also Q: 6.2..

6.6. Remote clients can’t connect
The X server now uses -nolisten tcp by default, which increases the security of the X server
by not opening a TCP/IP socket.
Use the -listen tcp option to allow the X server to open a TCP/IP socket as well, e.g.
startxwin -- -listen tcp. See Q: 4.2..
A better solution is to stop explicitly setting DISPLAY and allowing access using xhost or bydisabling access control. Use ssh -Y instead. (See the User’s Guide section on X forwarding usingssh (http://x.cygwin.com/docs/ug/using-remote-apps.html#using-remote-apps-ssh) for moredetails).

6.7. X sessions forwarded by PuTTY can’t connect. Non-cygwin local X clients can’t connect.
The X server now uses -nolisten tcp by default, which increases the security of the X server
by not opening a TCP/IP socket, only a local (UNIX domain) socket. Non-cygwin applications
cannot connect to that socket.

15

Cygwin/X Frequently Asked Questions
Use the -listen tcp option to allow the X server to open a TCP/IP socket as well, e.g.
startxwin -- -listen tcp. See Q: 4.2..
7. XDMCP connections
7.1. XDMCP fatal error: Session declined No valid address
Cygwin/X is sometimes unable to determine which local network interface’s address should bereported to the XDMCP server; in these cases you need to pass -fromlocal_host_name_or_ip_address to X to specify which interface address to report.
7.2. Why does Cygwin/X report AUDIT: client 1 rejected from IP remotehost?
The problem is most likely a wrong DNS (Network name resolution). Make sure your windows
host has a hostname which is valid from linux too and an IP address which linux can resolve to thathostname.
If you add a line
192.168.26.1 myhost

to /etc/hosts on the XDMCP server with the IP address and the hostname of your windows host thename resolution should work.

7.3. I get no login screen when using -query
A1: Disabled XDMCP on servers[Mika Laitio] For security reasons, XDMCP is not enabled by default on mostLinux/UNIX/*NIX/*BSD distributions (Red Hat, Mandrake, SuSE, FreeBSD, NetBSD, etc.) by
default. You have to manually enable remote logins to your X Display Manager (e.g. xdm, kdm, orgdm). The location of the proper config file is distribution/OS dependent, but a short list of known
config file locations is given in Table 1. You must change the line:[Xdmcp]Enable=false

to:[Xdmcp]Enable=trueor for xdm style configuration:
DisplayManager.requestPort:0

to:!DisplayManager.requestPort:

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Cygwin/X Frequently Asked Questions
Table 1. Known XDM Configuration File Locations
Distribution/OS

Version

Display Manager

LocationLinux Mandrake

8.1

kdm

/usr/share/config/kdm/kdmrc

Debian GNU/Linux

Unstablekdm/etc/kde3/kdm/kdmrc

Debian GNU/Linux

Unstablegdm/etc/X11/gdm/gdm.conf

Debian GNU/Linux

Unstablexdm/etc/X11/xdm/xdmconfig

Debian GNU/Linux

Unstablewdm/etc/X11/wdm/wdmconfig

A2: XDMCP and firewalls
XDMCP will not work correctly if you have a personal firewall installed or the built-in firewall ofWindows is activated.
The XDMCP protocol will send and receive data on port 177/UDP. But the actual connections will
be made to the local port 6000/TCP. It is safe to allow connections since the xserver has an own
security layer. An overview of used ports is given in Table 2.
Table 2. Ports used with XDMCP connections
Port

ProtocolDirection

Comment

177

UDP

Incoming/Outgoing

Actual XDMCPconnection

6000+display

TCP

Incoming

Connection for X11
clients. display isusually 0 except if you
specify it on thecommandline.

7.4. XDMCP does not work with Mandrake 8.1
See Q: 7.3.
7.5. Why does GDM not work with -clipboard
Newer versions of GDM have a more complex startup mechanism than the other display manager
have. This can interfere with the way the clipboard integration client is started.
Workaround: add (or modify) this section in the gdm.conf (or /etc/gdm/custom.conf) file.
[daemon]
KillInitClients=false

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Cygwin/X Frequently Asked Questions

7.6. I get no login screen for Solaris
See also Q: 7.7. and Q: 7.8.
[David Dawson] For whatever reason, certain versions of Solaris need fonts that are not provided
by Cygwin/X; the result is that you may see the Solaris background tile and the hourglass cursor,
but the XDM login prompt will never appear. The simplest solution is to point Cygwin/X at thefont server that is usually running on the Solaris machine. You’ll need a command line similar to
the following to start your XDMCP session and to connect to the Solaris font server:
X -query solaris_hostname_or_ip_address -fp
tcp/solaris_hostname_or_ip_address:7100
Note: The -fp parameter is a general X Server parameter, it is not specific to Cygwin/X;
therefore, the -fp is documented in the X Server manual page(http://x.cygwin.com/docs/man1/Xserver.1.html). For additional information about fonts, seeFonts in X11R6.7 (http://www.x.org/archive/X11R7.5/doc/fonts/fonts.html).

The standard port number for a font server is 7100, however, you may need to ask your systemadministrator what the font server port number is if you cannot connect to a font server on port
7100. It is also possible that your Solaris machine is not running a font server, in which case you
will need to consult your Solaris documentation for instructions on how to run a font server.

7.7. XDMCP freezes with remote Solaris machine!
See also Q: 7.6. and Q: 7.8.
Solaris appears to not support certain display bit depths, such as 24 bits per pixel. Change your
Windows display bit depth to 8, 16, or 32 and try logging in again. File a complaint with Sun if thisissue is important to you, or change your Solaris machines to use XFree86 instead of the Solaris X
Window System.
7.8. Login to CDE on Solaris via XDMCP hangs Cygwin/X.
See also Q: 7.6. and Q: 7.7.
Install the recommended set of patches (http://www.sun.com/bigadmin/patches/indexRec.html) for
your version of Solaris.
7.9. Where can I find more information about XDMCP.
See the Linux XDMCP HOWTO (http://en.tldp.org/HOWTO/XDMCP-HOWTO/) for more
information about XDMCP.
8. Troubleshooting

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Cygwin/X Frequently Asked Questions
8.1. Cygwin/X failed with "Fatal Error". What does this mean?
The Fatal Error is a general error message. More specific information what caused this is available
in /var/log/xwin/XWin.0.log. Please check the common error messages in
the Section called Error and Warning Messages. If your error is not mentioned proceed with
Q: 8.4.
8.2. Is there a log file that I can look at for diagnostic information and error messages?
Yes. The Cygwin/X log file is located at /var/log/xwin/XWin.0.log. You will find solutions
to the most common error messages in the Section called Error and Warning Messages.
8.3. I have a specific error message, what does it mean?
See the Error and Warning Messages section for help with specific error messages. Return to thissection if you do not find a specific answer for the error message that you have.
8.4. I have a specific error message that is not addressed in the Error and Warning Messages
section.
Search the Cygwin/X mailing list archives (https://cygwin.com/ml/cygwin/) to see if the error
message has already been reported and/or addressed. Report the error message to the
cygwin@cygwin.com mailing list, how the error message was caused, and the behavior of the X
Server after the error message was generated (exit, freeze, etc.), only if the error message has notbeen reported, if the circumstances that produced the error message are significantly different fromother reports, or if you have additional information regarding the error message to contribute.
Please include /var/log/xwin/XWin.0.log in your mail. This may help us identify the causeof your problem quicker.
8.5. My bug report the Cygwin/X mailing list was ignored. What do I do now?
Some bug reports are deliberately ignored by project members if the bug in question was recently
dealt with; did you search the mailing list archives (https://cygwin.com/ml/cygwin/) for a solution
to your problem before submitting your bug report? Some bug reports are ignored if they do notcontain sufficient information to understand the situation that produces the bug; did your bug
report have enough information? Some bug reports are missed or forgotten, thus some valid bug
reports do not receive a reply; simply resubmit such bug reports that have not received a response
within 7 days of submission.
8.6. Why does Cygwin/X freeze right after startup?
Zone Alarm 5 is known to break Cygwin/X. As a result you’ll see this line (or a similar) as last
output in /var/log/xwin/XWin.0.log
Rules = "xorg" Model = "pc101" Layout = "us" Variant = "(null)" Options = "(null)"Disabling Zone Alarm will not solve this problem. You can only uninstall Zone Alarm 5 andswitch to an earlier version (4.5 is known to work) or use a different personal firewall.
Another reason is /tmp mounted in textmode. This does only happen with the -multiwindow and-clipboard switches because of the extra threads within Cygwin/X.
You can remount /tmp to binmode with these commands:

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Cygwin/X Frequently Asked Questions
mount -b "$(cygpath -m /tmp)" /tmp

If this fails with an error message stating insufficient rights, try
mount -b -u "$(cygpath -m /tmp)" /tmp

8.7. Cygwin/X has very poor performance. What’s the reason?
Most likely you have installed some kind of personal firewall, VPN software or any other softwarethat modifies the TCP/IP stack of Windows. Especially Webwasher and some other filtering
software are known to slow down the network traffic.
Some online virus scanners like Symantec Antivirus do slowdown Cygwin/X a lot. They scan
every file access and network traffic which causes serious processing overhead beyond that fromthe X11 protocol and the unix emulation layer.
So far there is no known solution but to disable the virus scanner completely.

[Dr. Edward Wornar] Certain programs that are installed by various drivers and software packages
can consume an incredible amount of system resources and processing time. One known example
of such a program is ATI2evxx.exe, a utility installed with some ATI Technologies graphics card
drivers. Answers That Work (http://www.answersthatwork.com/) has information on
ATI2evxx.exe on their Task List Programs - A(http://www.answersthatwork.com/Tasklist_pages/tasklist_a.htm) page. You may want to try
disabling, one-by-one, ATI2evxx.exe and other such programs until you find the program that is
causing the slowdown.
8.8. I have Microsoft Services for Unix installed and can’t type anything. Help me!!!
Microsoft Services for Unix set some environment variables which points Cygwin/X to outdated or
not existing files. These variables are
XAPPLRESDIRXCMSDB
XKEYSYMDBXNLSPATH

To have Cygwin/X work correctly you have to unset at least XKEYSYMDB.
Reported by Juan Medina, Pavel Rozenboim

8.9. Cygwin/X is extremely slow, especially when using XDMCP to connect to remote machines.
see Q: 8.7..

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Cygwin/X Frequently Asked Questions
8.10. Simulated mouse wheel scrolling doesn’t work with a TrackPoint mouse (found on IBM
laptops) or Synaptics Touchpads[Gerald S. Williams] The TrackPoint driver tries to send scroll up/down messages to the default
scrollbar in a window. Cygwin/X does not use Windows scrollbars for X Client windows, so wemust configure the TrackPoint driver to send standard WM_MOUSEWHEEL messages to the
Cygwin/X window. This can be done by editing the TrackPoint configuration that can be found in
the tp4table.dat and/or tp4scrol.dat files, which are usually located in%SYSTEM_ROOT%\System32\, %PROGRAMFILES%\Synaptics\SynTP\ or%PROGRAMFILES%\Lenovo\Trackpoint\.
Add the following to the “Pass 0 rules”section and then restart your computer to ensure the driver
reloads it’s settings.
; X Windows*,*,XWin.exe,*,*,*,WheelStd,0,9

8.11. Why is the root window not shown in normal mode?
This question should be obsolete.
8.12. Why is the cross the default cursor in multiwindow mode?
This question should be obsolete
To workaround this add the command
run xsetroot -cursor_name left_ptr -fg white -bg black

to startxwin.bat

8.13. How can I adjust the linewidth in bash after resizing XTerm?
We think this question is probably obsolete
Try starting resize.

8.14. Why do some menus not work if Num-Lock is on?
The problem are programs which treat Num-Lock as modifier similar to Control. The programs
expect a plain click but received some strange Num-Lock-Click combination and can’t associate
this with the action "open menu".
9. Error and Warning Messages
9.1. _XSERVTransmkdir: Owner of /tmp/.X11-unix should be set to root
_XSERVTransmkdir: Owner of /tmp/.X11-unix should be set to root
_XSERVTransmkdir: ERROR: euid != 0,directory /tmp/.X11-unix will not be created21Cygwin/X Frequently Asked Questions
This question should be obsolete as this error is no longer generated.
This warning message can be ignored; it does not cause any known problems.

9.2. error opening security policy file /usr/X11R6/lib/X11/xserver/SecurityPolicy
This question should be obsolete as this error is no longer generated.
This error is harmless.

9.3. Duplicate invocation on display number: 0. Exiting.
Most likely you have started X twice.
if you start multiple instances of X you have to give then unique display numbers
X -query foo
X :1 -query bar
X :2 -query blubb

Specifying no display number is the same as using :0
If you want another terminal window (which in fact is just a convenient side effect of running
startxwin) you should do this by starting xterm & from an existing terminal window, from thenotification area icon menu, from a cygwin shell or from the start menu.

9.4. Fatal server error: could not open default font ’fixed’
This question should be obsolete as the default font is now built into the server.
This error occurs for one of three reasons:
1. You do not have a font package which provides the default font (’fixed’) installed. This israrely the problem; but in the event that it is the problem, just rerun Cygwin’ setup program,select the font-misc-misc package and install it.
2. The mount point for /usr/share/fonts/ was either invalid (does not point to a valid folder
on your system) or is a text-mode mount. You can confirm that this is the problem by running
mount from a Cygwin shell and checking the disk path returned for the/usr/share/fonts/ mount point.
Note: You cannot reliably fix this problem by deleting your Cygwin installation andreinstalling it. The mount points that Cygwin was using will be left in your system settings
and the invalid mount point for /usr/share/fonts/ will be used again when you performthe reinstallation. You SHOULD follow the instructions below to fix the problem.

To fix the problem, perform the following steps:
a. Open a Cygwin shell and run umount /usr/share/fonts/.
b. Close the Cygwin shell.
c. Run Cygwin’s setup program.

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Cygwin/X Frequently Asked Questions
d. For each of the font packages, if they are marked Keep, then select Reinstall, otherwise
leave them as they are:e. Allow Cygwin’s setup program to download and reinstall the fonts packages. The key tofixing this problem is that the files were previously untarred into an invalid location;
removing the mount point for the fonts directory should result in the files being untarred
to a valid location.
3. You chose "DOS/text" as the "Default Text File type" during Cygwin setup, ignoring theadvice that the Default Text File Type should be left on Unix/binary unless you have a very
good reason to switch it to DOS/text.
Open a Cygwin shell and run.
umount /usr/share/fonts/
mount -f -s -b "C:/cygwin/usr/share/fonts" "/usr/share/fonts"

Reinstall your fonts

9.5. Could not init font path element /usr/share/fonts/*/, removing from list!
These warnings are generally harmless since they indicate that default search paths for fonts do not
actually contain fonts; this is only a problem if the misc path does not contain fonts and/or all of
the paths do not contain fonts.
If you are getting these message and the X Server is also failing to start, then see Q: 9.4. for
information on how to fix your fonts.

9.6. The procedure entry point _check_for_executable could not be locatedThis question should be obsolete.
Programs that you are attempting to use were compiled against a newer version of Cygwin than iscurrently on your system. Run Cygwin’s setup program to update your installation to the latest
version.

9.7. cygX11-6.dll not found after installation or upgradeThis question should be obsolete.
9.8. Exception: STATUS_ACCESS_VIOLATION•

It is believed that this may have the same underlying causes as Q: 9.16.

• cygwin1.dll uses a shared memory section amongst all loaded copies of cygwin1.dll;

unfortunately, the layout and usage of the shared memory section changes between versions ofcygwin1.dll. Loading two different versions of cygwin1.dll will cause the shared memory
section to become corrupted, which almost always results in an Exception:
STATUS_ACCESS_VIOLATION. You must search your filesystem(s) and remove all copies ofcygwin1.dll except the copy in /bin. You must remove the different versions ofcygwin1.dll even if they are not in your path, as programs that depend on cygwin1.dll

23

Cygwin/X Frequently Asked Questions•attempt to load the file from the local directory before searching other paths; thus, it is rather
easy, and common, for multiple versions of cygwin1.dll to become loaded at the same time ifthey exist on a particular system.
See also this main Cygwin FAQ question(http://cygwin.com/faq.html#faq.setup.setup-fails-on-ts) for an issue which may cause thisproblem with older binaries on Terminal Server.

9.9. Xlib: connection to "local_host_name_or_ip_address:0.0" refused by server Xlib:
Maximum number of clients reachedCygwin/X queries getdtablesize() for the maximum number of client connections allowed; bydefault Cygwin returns 32 from getdtablesize(). Cygwin/X Server Test Series(http://x.cygwin.com/devel/server/) release Test44(http://x.cygwin.com/devel/server/changelog.html), released on 2001-08-15, changed the
maximum number of clients from 32 to 1024 by passing the square of getdtablesize() tosetdtablesize().
9.10. XIO: fatal IO error 104 (Connection reset by peer) on X server "127.0.0.1:0.0"
See Q: 9.9.
9.11. Cannot Open Display: 127.0.0.1:0.0
Certain classes of software, such as that used for Virtual Private Networking and fire-walling may
cause the IP address 127.0.0.1, or other local adapter addresses, to be redirected, to become
inoperable in some way, or to be operated in a manner that violates the defined operation of IP
address.
As a potential remedy, try removing all instances of such software; this may not always fix the
problem though, as some software may leave artifacts even after uninstallation is completed. The
only way to be sure that you have not found a Cygwin/X bug is to install Windows on a freshly
formatted hard drive, followed by Cygwin and Cygwin/X, and finally add your other software one
application at a time until Cygwin/X stops working.
Some products that have been reported to cause problems:••

Aventail Connect
Zonealarm PC Firewall from Zonelab
Note: These products may not cause problems in all configurations. However, the Cygwin/X
project has neither the time, ability, nor resources to help you correctly configure yourthird-party software.

See the main Cygwin FAQ question (http://cygwin.com/faq.html#faq.using.bloda) for an
up-to-date list of software which has been known to interfere with the correct operation of Cygwin.

9.12. Out of environment space
Increase your Windows environment space by following the instructions provided by Microsoft(http://support.microsoft.com/support/kb/articles/Q230/2/05.ASP).

24

Cygwin/X Frequently Asked Questions
9.13. Too many parameters
See Q: 9.12.
9.14. "xcb_xlib_lock: Assertion ’!c->xlib.lock’ failed." or "xcb_xlib_unlock: Assertion’c->xlib.lock’ failed."
This question should be obsolete.
Both of these represent bugs in a caller of libX11, and not in libX11 or libxcb. The first assertion
means that a caller attempted to lock the display while already locked. The second assertion meansthat a caller attempted to unlock the display without having it locked.
If you encounter such bugs, please report a bug against the offending software (which is not libX11
or libxcb)
This error can be worked around by using export LIBXCB_ALLOW_SLOPPY_LOCK=1

9.15. Fatal server error: Failed to activate core devices.

(EE) XKB: Could not invoke xkbcomp(EE) XKB: Couldn’t compile keymap
XKB: Failed to compile keymap
Keyboard initialization failed. This could be a missing or incorrect setup of xkeyboardFatal server error: Failed to activate core devices.

•••

Verify that xkeyboard-config is correctly installed using cygcheck -c xkeyboard-config,
Check that /usr/bin/xkbcomp can be run from a bash shell. If that fails, see if cygcheck/usr/bin/xkbcomp reports any missing DLLs.
Something is interferring with the ability of the X server to invoke xkbcomp to compile thekeymap.
See Q: 9.16. for possible causes.

9.16. "fatal error - unable to remap (some dll) to same address as parent: (some hex number) !=(some other hex number)" or "(some dll): Loaded to different address: parent(some hex number) !=child(some other hex number)"This is commonly caused by one of three things:•••

You have run Cygwin’s setup program to do an update while some cygwin processes wererunning, and then clicked on the continue option in the "In-use files detected" dialog, and thentried to carry on using Cygwin without rebooting as advised by setup. Reboot.
This is one of the symptoms of an application interfering with Cygwin’s fork() emulation. See
the main Cygwin FAQ question (http://cygwin.com/faq.html#faq.using.bloda) for a list of
software which has been known to interfere with the correct operation of Cygwin.
This also caused by DLLs with conflicting base addresses preventing Cygwin’s fork() emulationfrom functioning correctly. See the main Cygwin FAQ question(http://cygwin.com/faq.html#faq.using.fixing-fork-failures) for advice.

25

Cygwin/X Frequently Asked Questions
9.17. fork: child -1 - died waiting for longjmp before initialization, retry (some number), exit code(some hex number), errno (some other number)This is believed to have the same underlying causes as Q: 9.16.
10. Porting Software
10.1. Is there a list of software that has been ported to Cygwin/X?
Look in Cygwin’s setup program for packages in the X11 category.
10.2. How do I start porting software to Cygwin/X?
Cygwin/X provides a software interface that is very similar to the software interface provided by
GNU/Linux and other UNIX systems. Most software packages will compile on Cygwin/X without
any changes at all. To begin with, try to compile a given software package following that package’s
compilation instructions for GNU/Linux.
10.3. Are there common problems encountered when porting software to Cygwin/X?
One common problem encountered when porting software to Cygwin/X is due to Cygwin’s
inability to distinguish between files with the same name but different capitalization (e.g. XvMC.hand xvmc.h), which is due to a Windows’ limitation.
Example 1. Include Problems
This example is based off an error that actually occurred in the source code tree in
xc/programs/Xserver/Xext/xvmc.c. xvmc.c included XvMC.h, as shown below:#include "XvMC.h"

The intention was to include the file xc/include/extensions/XvMC.h. Unfortunately, there
was a file named xc/programs/Xserver/Xext/xvmc.h that ended up getting included insteadof the desired file, because the precompiler searched the local directory,
xc/programs/Xserver/Xext/, before searching the rest of the include path. Cygwin can’t
distinguish between XvMC.h and xvmc.h, so xvmc.h ended up being included in xvmc.c. The
build process on Cygwin broke because the contents of XvMC.h were entirely different than thecontents of xvmc.h.
The solution was to change the include to specifically reference the desired header:#include "../../../include/extensions/XvMC.h"10.4. Problems linking OpenGL applications? Undefined reference to _glsomething?
Cygwin has two OpenGL implementations:
1. headers in /usr/include/w32api/GL, libraries (-lglut32 -lglu32 -lopengl32) from the opengl andw32api packages which are for displaying OpenGL graphics directly through the native
Windows interface (Win32) without any X server
2. headers in /usr/include/GL, libraries (-lglut -lglu -lgl) from the Mesa libGL packages(libGL-devel, libGL1, libGLU-devel, libGLU1, libglut-devel, libglut3, freeglut) which are fordisplaying OpenGL graphics through an X server.

26

Cygwin/X Frequently Asked Questions
These are incompatible, even the headers (as the native OpenGL API has the stdcall calling
convention on x86), so you must exercise care if you have both sets of devel packages installed. An
application must be built using only one of these.
•••

X applications using GLX must be built using option 2.
Applications using GLUT have a choice.
Applications using the WGL API must be built using option 1.

(Words adapted from an email by AndrÃ© Bleau)
11. Contributing
11.1. Are there step-by-step instructions for contributing to Cygwin/X?
Yes. The Cygwin/X Contributor’s Guide (http://x.cygwin.com/docs/cg/cygwin-x-cg.html) has
step-by-step instructions for obtaining the source, building the source, building debug versions of
the source, and even cross-compiling under Linux.
11.2. Are there editors for Windows that understand and preserve UNIX end of line characters?
Yes. Emacs and XEmacs are available for Windows; they both understand and preserve UNIX endof line characters.
11.3. How should I generate patches for Cygwin/X?
Only submit patches that have UNIX end of line characters. See Q: 11.2. for information on editors
for Windows that are aware of UNIX end of line characters.
11.4. Where do I submit patches for Cygwin/X?
Submit patches for Cygwin/X to the cygwin@cygwin.com mailing list.
See Q: 11.3. for more information on generating patches.

11.5. Why doesn’t the X Window System use GNU’s autoconf?
It does! Thanks to the excellent efforts of the X.Org community, the X Window System has been
autotoolized since X.Org R7.0.
Anyone who despaired of touching the monolithic tree will find things much easier now withmodular packages.

11.6. What compiler does Cygwin/X use, and which compilers are supported?
Cygwin/X uses the gcc compiler from the Free Software Foundation. Cygwin/X source code ismostly ANSI C compliant, but we cannot guarantee that Cygwin/X will compile with any othercompiler, nor can we afford the time to support compilers other than gcc.
See the GCC Home Page (http://gcc.gnu.org) for more information on gcc.

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Cygwin/X Frequently Asked Questions
11.7. Is cross-compiling from a non-Cygwin platform supported?
Cross-compiling from a non-Cygwin platform is described in the Cygwin/X Contributor’s Guide(http://x.cygwin.com/docs/cg/cygwin-x-cg.html)
11.8. Where can I get help for installing DocBook on Cygwin?
The required packages are listed in the Cygwin/X Contributor’s Guide(http://x.cygwin.com/docs/cg/cygwin-x-cg.html).
12. Licenses, Patents, Trademarks, and Copyrights
12.1. What licenses apply to Cygwin/X source code?
Cygwin/X proper isn’t covered by a single license, as Cygwin/X is made up of two parts that arecovered by distinct licenses: Cygwin and the X Window System.
See Q: 12.2. and Q: 12.3. for more information regarding the licenses that apply to Cygwin/X.

12.2. What licenses apply to the X Window System source code?
X Window System source code is generally licensed under an X11 style license(http://cgit.freedesktop.org/xorg/xserver/tree/COPYING), which is certified by the Free Software
Foundation (http://www.gnu.org/licenses/license-list.html#GPLCompatibleLicenses) as
compatible with the GNU GPL.
12.3. What license applies to Cygwin source code?
Cygwin source code is licensed under a modified version of the GNU GPL(https://cygwin.com/licensing.html). Cygwin’s license modification specifically allows third-party
software under an open source license (http://opensource.org/licenses) to be linked with Cygwin
without requiring that the source code for the third-party software be distributed under the terms of
the GNU GPL. Cygwin’s developers went to great trouble to obtain this modification and shouldbe thanked for doing so, as without it the modification, Cygwin/X linking to Cygwin would be thesubject of endless discussion.
12.4. Who holds the copyright on the Cygwin/X source code?
Cygwin/X proper doesn’t have a single copyright holder, as Cygwin/X is made up of two parts,
namely Cygwin and the X Window System; each part follows a different scheme in regards to whowill hold the copyright on source code.
See Q: 12.5. and Q: 12.6. for more information regarding who holds the copyright on Cygwin/X
source code.

12.5. Who holds the copyright on the X Window System source code?
Each source code file in the X Window System typically has its own license and copyrightstatement. Therefore, there is not a general rule for determining who holds the copyright on aparticular X Window System source file, as each author is free to assign the copyright to someone28

Cygwin/X Frequently Asked Questions
else, to some group, or to keep the copyright themselves. You must inspect the source code file inquestion to determine who holds the copyright for that file.
12.6. Who holds the copyright on the Cygwin source code?
Red Hat (http://redhat.com/) owns the copyright on the Cygwin source code. Red Hat requires thatcopyright be assigned to Red Hat for non-trivial changes to Cygwin. You must fill out a copyrighttransfer form if you are going to contribute substantial changes to Cygwin.
12.7. What license applies to Motif?
Motif is a product of The Open Group (http://www.opengroup.org/). After many years under the
The Open Group Public License (http://www.opengroup.org/openmotif/license) (which does notsatisfy the Open Source Definition (http://opensource.org/docs/osd/) and is thus not compatible
with Cygwin’s license), Motif was released as free software under the LGPL v2.1 in October 2012.
12.8. Isn’t “XWin” trademarked by StarNet Communications?
Not in the USA, at least. A quick search at the United States Patent and Trademark Office(http://www.uspto.gov/) for “XWin” turns up one dead record and one live record. The live record
is for a logo belonging to a rock crusher manufacturer based out of Belgium. Neither trademark
affects Cygwin/X, as the dead record is no longer enforceable, while the live record is in an
unrelated and distinct industry; there cannot be confusion between rock crushers and computer
programs.

Bibliography

Books[ScheiflerGettys92] Robert W. Scheifler, James Gettys, Jim Flowers, and David Rosenthal, 1992,
1-55558-088-2, Butterworth-Heinemann, X Window System: The Complete Reference to Xlib, X
Protocol, ICCCM, and XLFD.
[Richter99] Jeffrey Richter, 1999, 1-57231-996-8, Microsoft Press, Programming Applications for
Microsoft Windows: Mastering the critical building blocks of 32-bit and 64-bit Windows-based
applications.
[Petzold99] Charles Petzold, 1999, 1-57231-995-X, Microsoft Press, Programming Windows: The
definitive guide to the Win32 API.
[McKay99] Everett N. McKay, 1999, 0-7356-0586-6, Microsoft Press, Developing User Interfaces for
Microsoft Windows: Practical and effective methods for improving the user experience.
[JonesOhlund99] Anthony Jones and Jim Ohlund, 1999, 0-7356-0560-2, Microsoft Press, Network
Programming for Microsoft Windows: Clear, practical guide to Microsoft’s networking APIs.
[Yuan01] Feng Yuan, 2001, 0-13-086985-6, Prentice Hall PTR, Windows Graphics Programming: Win32
GDI and DirectDraw.

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Cygwin/X Frequently Asked Questions[CohenWoodring98] Aaron Cohen and Mike Woodring, 1998, 1-56592-296-4, O’Reilly & Associates,
Inc., Win32 Multithreaded Programming: Building Thread-Safe Applications.
[CameronRosenblattRaymond96] Debra Cameron, Bill Rosenblatt, and Eric Raymond, 1996, 1991,
1-56592-152-6, O’Reilly & Associates, Inc., Learning GNU Emacs: UNIX Text Processing.
[Lewine91] Edited by Dale Dougherty, Donald A. Lewine, 1991, 0-937175-73-0, O’Reilly & Associates,
Inc., POSIX Programmer’s Guide: Writing Portable UNIX Programs.
[KernighanRitchie88] Brian W. Kernighan and Dennis M. Ritchie, 1988, 1978, 0-13-110370-9, PrenticeHall PTR, The C Programming Language: ANSI C.

GlossaryF
firewallFirewall software attempts to protect an internal network from intrusions originating from anexternal network.

V
Virtual Private Network
Virtual Private Networks are encrypted tunnels through which private data can be safely transmitted
over a private network (e.g. the Internet).

X
X Display Manager
An X Display Manager presents a graphical login screen to X users. Often an XDM will allow theuser to select a desktop environment or window manager to be for their login session. Some X
Display Managers are xdm, gdm (Gnome Display Manager), and kdm (KDE Display Manager).

30

Cygwin/X Frequently Asked Questions
X Display Manager Control Protocol
XDMCP allows XDM to process logins for users remote to the machine that XDM is running on;
login sessions will be run on the machine running XDM. For example, at a university you may use
XDMCP to login to an X session running on an engineering department computer from your dorm
room.
See Also: X Display Manager.
X11 Forwarding
Some SSH programs like OpenSSH provide a feature where in addition to the normal text channel
opened between the local and the remote host another encrypted channel is opened for thecommunication between the X11 client and the X11 server. The SSH server will act as proxy-server
for the X11 clients and will forward all communication to the X11 server.

A. GNU Free Documentation License
Version 1.3, 3 November 2008
Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc. (http://www.fsf.org/)
Everyone is permitted to copy and distribute verbatim copies of this license document, but changing it is
not allowed.

0. PREAMBLE
The purpose of this License is to make a manual, textbook, or other functional and useful document“free” in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, withor without modifying it, either commercially or noncommercially. Secondarily, this License preserves forthe author and publisher a way to get credit for their work, while not being considered responsible formodifications made by others.
This License is a kind of “copyleft”, which means that derivative works of the document mustthemselves be free in the same sense. It complements the GNU General Public License, which is a
copyleft license designed for free software.
We have designed this License in order to use it for manuals for free software, because free softwareneeds free documentation: a free program should come with manuals providing the same freedoms thatthe software does. But this License is not limited to software manuals; it can be used for any textual
work, regardless of subject matter or whether it is published as a printed book. We recommend thisLicense principally for works whose purpose is instruction or reference.

1. APPLICABILITY AND DEFINITIONSThis License applies to any manual or other work, in any medium, that contains a notice placed by the
copyright holder saying it can be distributed under the terms of this License. Such a notice grants aworld-wide, royalty-free license, unlimited in duration, to use that work under the conditions statedherein. The “Document”, below, refers to any such manual or work. Any member of the public is a31

Cygwin/X Frequently Asked Questions
licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in away requiring permission under copyright law.
A “Modified Version” of the Document means any work containing the Document or a portion of it,either copied verbatim, or with modifications and/or translated into another language.
A “Secondary Section” is a named appendix or a front-matter section of the Document that deals
exclusively with the relationship of the publishers or authors of the Document to the Document’s overall
subject (or to related matters) and contains nothing that could fall directly within that overall subject.
(Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any
mathematics.) The relationship could be a matter of historical connection with the subject or with related
matters, or of legal, commercial, philosophical, ethical or political position regarding them.
The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those ofInvariant Sections, in the notice that says that the Document is released under this License. If a section
does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The
Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections
then there are none.
The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-CoverTexts, in the notice that says that the Document is released under this License. A Front-Cover Text may
be at most 5 words, and a Back-Cover Text may be at most 25 words.
A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose
specification is available to the general public, that is suitable for revising the document
straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or(for drawings) some widely available drawing editor, and that is suitable for input to text formatters orfor automatic translation to a variety of formats suitable for input to text formatters. A copy made in anotherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart ordiscourage subsequent modification by readers is not Transparent. An image format is not Transparent if
used for any substantial amount of text. A copy that is not “Transparent” is called “Opaque”.
Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input
format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming
simple HTML, PostScript or PDF designed for human modification. Examples of transparent image
formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read andedited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools
are not generally available, and the machine-generated HTML, PostScript or PDF produced by someword processors for output purposes only.
The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed
to hold, legibly, the material this License requires to appear in the title page. For works in formats which
do not have any title page as such, “Title Page” means the text near the most prominent appearance of thework’s title, preceding the beginning of the body of the text.
The “publisher” means any person or entity that distributes copies of the Document to the public.
A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ
or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ
stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”,“Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify theDocument means that it remains a section “Entitled XYZ” according to this definition.

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Cygwin/X Frequently Asked Questions
The Document may include Warranty Disclaimers next to the notice which states that this License
applies to the Document. These Warranty Disclaimers are considered to be included by reference in thisLicense, but only as regards disclaiming warranties: any other implication that these Warranty
Disclaimers may have is void and has no effect on the meaning of this License.

2. VERBATIM COPYING
You may copy and distribute the Document in any medium, either commercially or noncommercially,
provided that this License, the copyright notices, and the license notice saying this License applies to theDocument are reproduced in all copies, and that you add no other conditions whatsoever to those of thisLicense. You may not use technical measures to obstruct or control the reading or further copying of thecopies you make or distribute. However, you may accept compensation in exchange for copies. If you
distribute a large enough number of copies you must also follow the conditions in section 3.
You may also lend copies, under the same conditions stated above, and you may publicly display copies.

3. COPYING IN QUANTITY
If you publish printed copies (or copies in media that commonly have printed covers) of the Document,
numbering more than 100, and the Document’s license notice requires Cover Texts, you must enclose thecopies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front
cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as
the publisher of these copies. The front cover must present the full title with all words of the title equallyprominent and visible. You may add other material on the covers in addition. Copying with changes
limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, canbe treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed(as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100, you must either
include a machine-readable Transparent copy along with each Opaque copy, or state in or with each
Opaque copy a computer-network location from which the general network-using public has access todownload using public-standard network protocols a complete Transparent copy of the Document, freeof added material. If you use the latter option, you must take reasonably prudent steps, when you begin
distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessibleat the stated location until at least one year after the last time you distribute an Opaque copy (directly or
through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the Document well before redistributing
any large number of copies, to give them a chance to provide you with an updated version of theDocument.

4. MODIFICATIONS
You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and3 above, provided that you release the Modified Version under precisely this License, with the Modified
Version filling the role of the Document, thus licensing distribution and modification of the Modified
Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

33

Cygwin/X Frequently Asked Questions
A. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and fromthose of previous versions (which should, if there were any, be listed in the History section of theDocument). You may use the same title as a previous version if the original publisher of that version
gives permission.
B. List on the Title Page, as authors, one or more persons or entities responsible for authorship of themodifications in the Modified Version, together with at least five of the principal authors of theDocument (all of its principal authors, if it has fewer than five), unless they release you from thisrequirement.
C. State on the Title page the name of the publisher of the Modified Version, as the publisher.
D. Preserve all the copyright notices of the Document.
E. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
F. Include, immediately after the copyright notices, a license notice giving the public permission to use
the Modified Version under the terms of this License, in the form shown in the Addendum below.
G. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in
the Document’s license notice.
H. Include an unaltered copy of this License.
I. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least thetitle, year, new authors, and publisher of the Modified Version as given on the Title Page. If there isno section Entitled “History” in the Document, create one stating the title, year, authors, andpublisher of the Document as given on its Title Page, then add an item describing the Modified
Version as stated in the previous sentence.
J. Preserve the network location, if any, given in the Document for public access to a Transparent copyof the Document, and likewise the network locations given in the Document for previous versions it
was based on. These may be placed in the “History” section. You may omit a network location for awork that was published at least four years before the Document itself, or if the original publisher ofthe version it refers to gives permission.
K. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section,and preserve in the section all the substance and tone of each of the contributor acknowledgements
and/or dedications given therein.
L. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section
numbers or the equivalent are not considered part of the section titles.
M. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified
Version.
N. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any
Invariant Section.
O. Preserve any Warranty Disclaimers.
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary
Sections and contain no material copied from the Document, you may at your option designate some or
all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the
Modified Version’s license notice. These titles must be distinct from any other section titles.

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Cygwin/X Frequently Asked Questions
You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your
Modified Version by various parties — for example, statements of peer review or that the text has been
approved by an organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a
Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage ofFront-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any
one entity. If the Document already includes a cover text for the same cover, previously added by you or
by arrangement made by the same entity you are acting on behalf of, you may not add another; but you
may replace the old one, on explicit permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission to use theirnames for publicity for or to assert or imply endorsement of any Modified Version.

5. COMBINING DOCUMENTS
You may combine the Document with other documents released under this License, under the terms
defined in section 4 above for modified versions, provided that you include in the combination all of theInvariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections ofyour combined work in its license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections
may be replaced with a single copy. If there are multiple Invariant Sections with the same name but
different contents, make the title of each such section unique by adding at the end of it, in parentheses,
the name of the original author or publisher of that section if known, or else a unique number. Make thesame adjustment to the section titles in the list of Invariant Sections in the license notice of the combinedwork.
In the combination, you must combine any sections Entitled “History” in the various original documents,
forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”,
and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements”.

6. COLLECTIONS OF DOCUMENTS
You may make a collection consisting of the Document and other documents released under this License,
and replace the individual copies of this License in the various documents with a single copy that isincluded in the collection, provided that you follow the rules of this License for verbatim copying of eachof the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under thisLicense, provided you insert a copy of this License into the extracted document, and follow this License
in all other respects regarding verbatim copying of that document.

7. AGGREGATION WITH INDEPENDENT WORKS
A compilation of the Document or its derivatives with other separate and independent documents orworks, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright
resulting from the compilation is not used to limit the legal rights of the compilation’s users beyond what
the individual works permit. When the Document is included in an aggregate, this License does not apply
to the other works in the aggregate which are not themselves derivative works of the Document.

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Cygwin/X Frequently Asked Questions
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if theDocument is less than one half of the entire aggregate, the Document’s Cover Texts may be placed on
covers that bracket the Document within the aggregate, or the electronic equivalent of covers if theDocument is in electronic form. Otherwise they must appear on printed covers that bracket the wholeaggregate.

8. TRANSLATION
Translation is considered a kind of modification, so you may distribute translations of the Document
under the terms of section 4. Replacing Invariant Sections with translations requires special permission
from their copyright holders, but you may include translations of some or all Invariant Sections inaddition to the original versions of these Invariant Sections. You may include a translation of thisLicense, and all the license notices in the Document, and any Warranty Disclaimers, provided that you
also include the original English version of this License and the original versions of those notices anddisclaimers. In case of a disagreement between the translation and the original version of this License ora notice or disclaimer, the original version will prevail.
If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, therequirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.

9. TERMINATION
You may not copy, modify, sublicense, or distribute the Document except as expressly provided under
this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and willautomatically terminate your rights under this License.
However, if you cease all violation of this License, then your license from a particular copyright holder isreinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates yourlicense, and (b) permanently, if the copyright holder fails to notify you of the violation by somereasonable means prior to 60 days after the cessation.
Moreover, your license from a particular copyright holder is reinstated permanently if the copyrightholder notifies you of the violation by some reasonable means, this is the first time you have received
notice of violation of this License (for any work) from that copyright holder, and you cure the violation
prior to 30 days after your receipt of the notice.
Termination of your rights under this section does not terminate the licenses of parties who have received
copies or rights from you under this License. If your rights have been terminated and not permanently
reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.

10. FUTURE REVISIONS OF THIS LICENSE
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation
License from time to time. Such new versions will be similar in spirit to the present version, but may
differ in detail to address new problems or concerns. See Copyleft (http://www.gnu.org/copyleft/).
Each version of the License is given a distinguishing version number. If the Document specifies that a
particular numbered version of this License “or any later version” applies to it, you have the option offollowing the terms and conditions either of that specified version or of any later version that has been
published (not as a draft) by the Free Software Foundation. If the Document does not specify a version
number of this License, you may choose any version ever published (not as a draft) by the Free Software

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Cygwin/X Frequently Asked Questions
Foundation. If the Document specifies that a proxy can decide which future versions of this License canbe used, that proxy’s public statement of acceptance of a version permanently authorizes you to choosethat version for the Document.

11. RELICENSING“Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server thatpublishes copyrightable works and also provides prominent facilities for anybody to edit those works. A
public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration”(or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.
“CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative
Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco,California, as well as future copyleft versions of that license published by that same organization.
“Incorporate” means to publish or republish a Document, in whole or in part, as part of another
Document.
An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were firstpublished under this License somewhere other than this MMC, and subsequently incorporated in whole
or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated priorto November 1, 2008.
The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on thesame site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents
To use this License in a document you have written, include a copy of the License in the document andput the following copyright and license notices just after the title page:
Copyright © YEAR YOUR NAME
Permission is granted to copy, distribute and/or modify this document under theterms of the GNU Free Documentation License, Version 1.3 or any later version
published by the Free Software Foundation; with no Invariant Sections, no
Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in
the section entitled “GNU Free Documentation License”.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with. . . Texts.”
line with this:with the Invariant Sections being LIST THEIR TITLES, with the Front-Cover Texts
being LIST, and with the Back-Cover Texts being LIST.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those
two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing theseexamples in parallel under your choice of free software license, such as the GNU General Public
License, to permit their use in free software.

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