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====== Installing and configuring an X server ======


<WRAP center round tip 60%>
This detailed and easy-to-understand page will help you **set up things correctly on your own**, and help you **understand what you are doing**

Or you can ask somebody to quickly configure everything for you, and keep on believing that things work by magic...
</WRAP>


===== What is an X server? =====

  * An //X server// **is not** a server for distributing your perfect models output!

  * An //X server// **is** basically a program running on your **local** computer that understands the [[https://en.wikipedia.org/wiki/X_Window_System_core_protocol|X Windows System protocol]] used by **Linux computers** (**local** computer, or **remote** Linux servers) to generate graphics, and that can //render// (i.e. display) the graphics generated **remotely** on your **local** computer

  * This page will mention a //''DISPLAY'' variable// several times: the X server needs this in order to know **where to display the graphics**!
===== What do we mean exactly with Local and Remote computers? =====

This page will very often mention **local computers**, and **remote computers**:

  * The **local computer** is the desktop or laptop you are interacting with (using a screen+mouse+keyboard)
    * The local computer can be a **Linux, Windows or Mac (i.e //OS X//) computer**

  * The **remote computer or server** is another computer that you also want to interact with (using the screen+mouse+keyboard of your local computer)
    * [[other:ssh#connecting_to_servers_commonly_used_by_lsce_users|Some servers used by LSCE users]]
    * We only consider on this page the case of a **remote //Linux// machine** that **requires a local running //X server//**

  * **Remote Linux machine** can mean several things:
    * It can be another operating system running inside **a [[https://en.wikipedia.org/wiki/Virtual_machine|Virtual Machine]] on your local computer**
      * We mostly consider on this page the case of a **Linux virtual machine** using [[other:win10wsl|Windows Subsystem for Linux (WSL)]] on a **local Windows computer**, but this can apply to other configurations
    * It can be a **distant Linux computer or server** in your building, or a high performance Linux computer in a computing center on the other side of the Earth. It could also be a Linux virtual machine in the //Cloud//
===== Using an X server on Linux =====

<WRAP center round tip 60%>
You don't need to do anything special!
</WRAP>

Linux computers come pre-configured with a running //X server// that will display the graphics generated locally and on remote Linux servers


===== Using an X server on Windows =====

There are several available options

==== Installing VcXsrv ====

<note tip>''VcXsrv'' is **pre-installed on the LSCE Windows computers**!

  * You may want to check if a more recent version is available
  * You surely want to follow the configuration steps, in order to get the best possible settings to work with PuTTY!
</note>

Type: <wrap em>free</wrap>

Download the installer from [[https://sourceforge.net/projects/vcxsrv/|VcXrsv]] and install ''VcXsrv''.

=== VcXsrv Configuration ===

You need to configure ''VcXsrv'' to work in //multiple windows// mode. The following steps will show you how to create a shortcut on your desktop to start ''VcXsrv'' in this appropriate mode

  * Start the //configuration tool//: ''Start'' => ''VcXsrv'' => ''Xlaunch''
  * Select ''Multiple windows'', then ''Next''
  * Select ''Start no client'', then ''Next''
  * Keep the default ''Clipboard'' settings, uncheck ''Native opengl'', then ''Next''
    * You can check the [[other:x_conf#opengl_related_settings|OpenGL discussion section]] if you have time...
  * Click on ''Save configuration'' and save an ''X_Server.xlaunch'' configuration file on your Desktop, then ''Terminate''.\\ You should now have a new ''X_Server'' icon/shortcut on your Desktop
  * Start the server by double-clicking on the new ''X_Server'' icon
    * It will seem that nothing happens, but an ''X'' icon will appear in the right side of the taskbar (you may have to look for it in the //Display hidden icons// pull-up menu). Your computer is now ready to display remote graphics!\\ {{ :other:vcxsrv_x.png?direct |}}
    * The X server will stop when you close your Windows session or restart the computer. Do not forget to click on the ''X_Server'' icon on your desktop if you know that you will need an X server later
      * FIXME Document how to automatically start the X server...
    * Note: you can right-click on the ''X'' icon and select ''Exit...'' if you need to quit the X server


==== Installing x410 ====

<WRAP center round tip 60%>
[[https://token2shell.com/x410/|x410]] is a **low cost** commercial //X server// that can be directly installed from the [[https://www.microsoft.com/store/productId/9NLP712ZMN9Q|Microsoft store]].

This is an //X server//, and you will get the same functionalities as what is already provided for free by [[other:x_conf#installing_vcxsrv|VcXsrv]], **but**:
  * Once installed, ''x410'' will be automatically updated by the Microsoft Store application
  * If you move to another computer, you can install ''x410'' again by just [[other:win10config#connecting_to_the_microsoft_store|Connecting the Microsoft Store to your MS account]] on the new computer. No need to buy ''x410'' again !
  * There seems to be more (useful) updates than for ''VcXsrv''
  * The interface is more modern, with more options, and there is a lot of useful information on the web site
  * The ''x410'' name is easier to remember! :-D
</WRAP>


Type: <wrap em>commercial</wrap>

Buy and install ''x410'' from the [[https://www.microsoft.com/store/productId/9NLP712ZMN9Q|Microsoft store]]

=== x410 configuration ===

  * Start ''x410'': ''Start'' => ''X410''
    * It will seem that nothing happens, but an ''X'' icon will appear in the right side of the taskbar (you may have to look for it in the //Display hidden icons// pull-up menu). Your computer is now //almost// ready to display remote graphics!\\ {{ :other:x410_x.png?direct |}}
  * Right-click on the ''X'' icon to open the **X410 settings**
    * Select ''Auto copy to Windows after selection''\\ {{ :other:x410_settings.png?direct |}} and click somewhere else on the desktop to close the settings
  * It is possible to **automatically start ''x410''** when you open your session! Otherwise, it will stop when you close your Windows session or restart the computer, and you will have to restart it by hand (''Start'' => ''X410'') if you know that you will need an X server later
    * Open the **Windows Task Manager** (Right-click on ''Start'' and select ''Task Manager'')
    * Go to the ''Startup'' panel (if there are no panels, select ''More details'')
    * Right-click on ''X140'' and select ''Enabled''
  * Note: if you need to quit the //X server//, you can right-click on the ''X'' icon, and then click on the //Display// number at the lower left (usually ''0'') and select ''Shut down'' 

===== Using an X server on a Mac =====

==== Installing XQuartz ====

Type: <wrap em>free</wrap>

Download the installer from [[https://www.xquartz.org|XQuartz]] and install it

=== XQuartz configuration ===

<WRAP center round tip 60%>
Nothing to configure!
</WRAP>

The ''XQuartz'' //X server// will be automatically started, if a graphical application needs it!

Check the [[https://support.apple.com/guide/terminal/script-management-with-launchd-apdc6c1077b-5d5d-4d35-9c19-60f2397b2369/mac|launchd documentation]] if you need more details
<code>$ launchctl list | grep quartz
         -	0	org.xquartz.startx</code>
===== Configuration on the remote Linux server =====

==== If you are connecting with ssh or PuTTY ====

Nothing special to do, if you are using [[other:ssh#using_an_x_server_to_display_graphics|"ssh -X" or "ssh -Y"]] or a [[other:putty_conf#changing_some_useful_settings|correctly configured PuTTY]] to connect to a remote Linux server

==== If you are using Windows Subsystem for Linux ====

In that special case, you will need the //X server// to display graphics [[other:x_conf#what_do_we_mean_exactly_with_local_and_remote_computers|from the local virtual machine and from remote computers]]

You have to make sure that the ''DISPLAY'' variable is correctly [[other:win10wsl#configuration_in_your_local_linux_account|defined in the terminals used in WSL]]
===== Testing =====

==== Testing plan ====

The idea is to:
  * Open a terminal and check that the ''DISPLAY'' environment variable is defined on the local machine
    * If we use [[other:win10wsl|WSL]], we also check that we can start an application using graphics in ''WSL''
  * Connect to the remote machine
  * Check that a (new) ''DISPLAY'' variable is automatically defined on the remote machine
  * Check that we can start an application using graphics on the remote machine

Test application:
  * We need a simple graphical application that is likely to be already installed on the remote machine
    * The **test is declared successful** if we get a new window and we can interact with it.\\ Note: some applications may start with their window iconified, and you may have to check the part of your screen where the iconified windows go...
    * Do not forget to **cleanly quit the test application** when you have checked that it seems to work
    * It's enough to test one application
  * ''xterm &'': the **recommended test application**. It will open a new terminal on the remote machine
  * ''xeyes &'', ''xclock &'', ''gvim &'', ''gedit &'', ''eog &'', ''evince &'', ... : other //standard// applications, that may be installed (or not)

The test may fail, due to the [[other:x_conf#nothing_works|usually expected errors]]
==== On a Linux computer or a Mac ====

Open a //terminal// ([[other:ssh#a_recommended_terminal_for_mac|terminal on a Mac]]) and use some basic commands to check things

<code>[Local] $ hostname
name_of_your_local_machine

[Local] $ echo $DISPLAY
:0

[Local] $ ssh -X some_login@some_remote_server
[some connection information skipped here]

[Remote] $ hostname
name_of_the_remote_server

[Remote] $ echo $DISPLAY
localhost:20.0

[Remote] $ xterm &</code>

==== On a Windows computer with only an X server installed ====

We just open a ''Powershell'' window (''Start'' => ''Windows Powershell'' => ''Windows Powershell'') and type some basic commands, including the creation of a ''DISPLAY'' variable

<code>PS C:\> $env:computername
name_of_your_local_machine

PS C:\> $env:DISPLAY
PS C:\> $env:DISPLAY="localhost:0"
PS C:\> $env:DISPLAY
localhost:0

PS C:\> ssh -Y some_login@some_remote_server
Warning: No xauth data; using fake authentication data for X11 forwarding.
[some connection information skipped here]

[Remote] $ hostname
name_of_the_remote_server

[Remote] $ echo $DISPLAY
localhost:19.0

[Remote] $ xterm &</code>


==== On a Windows computer with PuTTY and an X server installed ====

We assume here that [[other:putty_conf|PuTTY is already installed and configured]] and **correctly** configured (with ''Enable X11 forwarding'')

We just have to open a pre-configured //PuTTY Session// on a remote server
<code>[Remote] $ hostname
name_of_the_remote_server

[Remote] $ echo $DISPLAY
localhost:19.0

[Remote] $ xterm &</code>


==== On a Windows computer with WSL+Linux and an X server installed ====

We assume that [[other:win10wsl|WSL+Ubuntu]] is installed and that the ''DISPLAY'' variable is [[other:x_conf#if_you_are_using_windows_subsystem_for_linux|configured correctly]]

Open a //WSL// terminal (you should know how, if you have installed //WSL//) and type some basic commands

<code>[Local WSL] $ hostname
name_of_your_local_machine

[Local WSL] $ echo $DISPLAY
localhost:0.0

[Local WSL] $ xterm &

[Local WSL] $ ssh -X some_login@some_remote_server
[some connection information skipped here]

[Remote] $ echo $DISPLAY
localhost:22.0

[Remote] $ xterm &</code>





===== Troubleshooting =====


==== Nothing works! ====

That's unfortunate, but:
  * Have you turned on your computer? :-P
  * Do you have network access, and an account on a remote server? :-?
  * Have you run the [[other:x_conf#testing|Tests]]?
  * Have you [[other:x_conf|installed and configured the X server]] correctly? Is it really running?
  * Have you configured [[other:putty_conf|PuTTY]] and/or other required applications correctly ?
  * Is the [[other:x_conf#what_is_an_x_server|DISPLAY variable]] defined correctly on the local and remote computer?


==== Error when there is no X server running ====

If the ''DISPLAY'' variable is defined, but there is **no X server**, you will get a ''Can't open display: localhost://[SOME VALUE]//'' error

<code>$ xterm &
xterm: Xt error: Can't open display: localhost:23.0</code>

Time to [[other:x_conf|read this page again]]...

==== Error when there is no space left in your home directory ====

If there is no space left in your home directory (usually the home directory of the remote server), or if you have exceeded your [[other:newppl:starting#which_disks_should_you_use|home disk quota]], you will get an error similar to [[#error_when_there_is_no_x_server_running|Error when there is no X server running]]

<code>$ xterm &
xterm: Xt error: Can't open display: localhost:23.0</code>

**Solution**: clean the content of your //home//!
==== Error when DISPLAY is not defined correctly ====

If the ''DISPLAY'' **variable is not defined (correctly)**, you will get a ''Can't open display: //[NO VALUE DISPLAYED HERE]//'' error

<code>$ xterm &
$ xterm: Xt error: Can't open display:
xterm: DISPLAY is not set
$ echo $DISPLAY

$ setenv DISPLAY CRAP_DISPLAY
$ xterm
xterm: Xt error: Can't open display: CRAP_DISPLAY
</code>

Make sure that you are using ''ssh -X'' or ''ssh -Y'', or that [[other:putty_conf#changing_some_useful_settings|PuTTY is configured]] with ''Enable X11 forwarding''


==== Can't start a graphical application by clicking on its desktop shortcut ====

Check the shortcut and run the command directly in a terminal to check the error message

There is a good chance that [[other:x_conf#error_when_there_is_no_x_server_running|you have forgotten to start the X server!]]


==== OpenGL related settings ====

It's hard to know what the best //OpenGL// settings for your //X server// are: it depends on your local computer, the remote computer, the network speed, the application generating the graphics, the libraries' versions...

  * If ''Native opengl'' is activated in ''VcXsrv'', you //may// have to also use the following environment variable on the remote computer: ''export LIBGL_ALWAYS_INDIRECT=1''
    * or maybe not! You can try to understand the [[https://unix.stackexchange.com/questions/1437/what-does-libgl-always-indirect-1-actually-do|What does LIBGL_ALWAYS_INDIRECT=1 actually do?]] thread...

==== Blurry display ====

  * If you use ''VcXsrv'' and the content of some displayed //X windows// appear **blurry**, see if you can [[other:win10misc#vcxsrv_x_server|fix the compatibility settings]], or try to use **x410**.


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