Differences

This shows you the differences between two versions of the page.

--- other:x_conf [2022/08/08 15:05] – [Installing VcXsrv] jypeter
+++ other:x_conf [2022/08/09 10:53] – [Using an X server on Linux] jypeter
@@ Line 3: / Line 3: @@
 ===== What is an X server? =====
-An //X server// is not a server for distributing your perfect models output!
+  * 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 **remote Linux servers** to generate graphics, and that can //render// (i.e. display) the graphics generated remotely on your **local computer**.
+  * 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
+===== What do we mean exactly with Local and Remote computers? =====
+This page will very often mention **local computers** or **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)
+    * 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 Windows computer, but this can apply to other configurations
+    * It can be a **distant computer** or server in your building, or a high performance computer in a computing center on the other side of the Earth. It could also be a virtual machine in the //Cloud//
 ===== Using an X server on Linux =====
-Linux computers come pre-configured with a running X server (because they need it for displaying local graphics) that will display the graphics generated locally and on remote Linux servers. **You don't need to do anything special!**
+<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
@@ Line 75: / Line 94: @@
   * 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 an Apple computer =====
-**Starting, configuring and exiting X410**: you can start X410 by clicking on it in the Windows Start Menu, or choose to [[https://token2shell.com/howto/x410/automatically-start-x410-on-login/|Automatically Start X410 on Login]]
-  * Note: nothing actually happens when you start X410, as it is just waiting to display graphics! You will just get a new **X** icon in the //hidden// icons of the taskbar.
-  * You can configure (and exit) X410 by right clicking on its **X** icon
+===== Configuration on the remote Linux server =====
-===== Using an X server on an Apple computer =====
+==== 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 ''PuTTY'' to connect to a remote Linux server
-===== Configuration on the remote machine =====
+==== If you are using WSL ====
-==== If you are connecting with ssh ====
+You need to know what you consider as the //Local machine//, and what is the //Remote server//
-Nothing special to do!
+  * **Local machine**: your local **Windows computer**, where you have installed [[other:win10wsl|WSL+Ubuntu]]
-==== If you are using WSL ====
-If you have installed [[other:win10wsl|WSL+Ubuntu]] on your local machine, and you need your X server to display graphics generated in WSL, you need to define the DISPLAY variable: ''export DISPLAY=localhost:0.0''
+  * **Remote server** : we consider 2 types of remote servers:
+    * an **actual remote server**
+    * The **WSL computer** running on a **virtual machine inside your local Windows computer**. This can be considered as a different and //remote// computer, even it is running on the local computer\\ You need your local //X server// to display graphics generated in WSL
+    * **Define the ''DISPLAY'' variable** in the terminals used in WSL:
+      * //bash// shell: ''export DISPLAY=localhost:0.0''
+      * //tcsh// shell: ''setenv DISPLAY localhost:0.0''
+      * You probably want to define the ''DISPLAY'' variable automatically in one of the shell configuration files
@@ Line 100: / Line 123: @@
   * Open a terminal and check that the ''DISPLAY'' environment variable is correctly defined on the local machine
   * Connect to the remote machine
-  * Check that a (new) ''DISPLAY'' variable is defined on the remote machine
+  * Check that a (new) ''DISPLAY'' variable is automatically defined on the remote machine
   * Check that you can start an application using graphics (e.g. ''xterm'') on the remote machine
@@ Line 151: / Line 174: @@
 ==== On a Windows computer with PuTTY and an X server installed ====
-We assume here that [[other:putty_conf|PuTTY is already installed and configured]]
+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 //Session// on a remote server
+We just have to open a pre-configured //PuTTY Session// on a remote server
 <code>[Remote] $ hostname
 name_of_the_remote_server
@@ Line 165: / Line 188: @@
 ==== 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_wsl|configured correctly]]
-  * FIXME ''export DISPLAY=localhost:0.0''
+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 =====
@@ Line 180: / Line 215: @@
   * Have you configured [[other:putty_conf|PuTTY]] and/or other required applications correctly ?
   * Is the ''DISPLAY'' variable defined correctly on the local and remote computer?
+=== 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 $DISPLAY
+</code>
+Make sure that you are using ''ssh -X'' or ''ssh -Y'', or that [[other:putty_conf#changing_some_useful_settings|PuTTY is configured]] with ''Enable X11 forwarding''
+=== When there is no X server running ===
+If the ''DISPLAY'' variable is defined, but there is **no X server**, you will get a ''Can't open display: localhost://[SOME VALUE]//'' error\\ <code>$ xterm &
+$ connect localhost port 6000: Connection refused
+xterm: Xt error: Can't open display: localhost:12.0</code>
+Time to [[other:x_conf|read this page again]]...
 ==== 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...
+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''
+  * 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...