What is X ?
X is the GUI for graphical bitmap displays and is very commonly seen on Linux OS. X originated at MIT in 1984 as part of project Athena which provided computing env using dissimilar hardware. The name 'X' is a pun on the name of its predecessor called the 'W' Windows that was developed in Stanford. This project was started by a MIT member Bob Scheifler. In terms of functionality, Linux Operating System is more configurable than Microsoft's Windows Operating System. Eg, in Microsoft Windows you can't turn off the gui where as in Linux the gui (X) is just another process and therefore can be started and stopped as you like.
Here are some detailed notes about X for review:
-X Window System = X11 = X = a window system for graphical bitmap displays.
-X separates display functions into a display server and clients.
-X is network transparent.
-X's way of treating client and server is opposite to the traditional way of treating client and server.
-X outputs display and inputs keyboard, mice, touchscreen input.
-X provides a toolkit for GUI but does not specify any user interface. That choice is left to the user. The common choices are Gnome or KDE.
-X is currently maintained by a non-profit org called X.org.
-X server is governed by /etc/X11/xorg.conf
-When the following cmd is run, it produces a temporary file called "/root/xorg.conf.new"
# Xorg -configure
-To test the above file, run:
# X-config /root/xorg.conf.new
-If the X server runs fine, then copy the file to /etc/X11/xorg.conf
-If the following cmd returns a "Fatal server error" then remove the file in the error and retry.
-Good Practices:
-save a copy of the /etc/X11/xorg.conf file before overwriting it.
-for troubleshooting, look into /var/log/messages and /var/log/xorg.0.log
-Three ways to start X:
- run "X &" or "startx" cmd manually
- run init 5 or telinit 5
- edit /etc/inittab and reboot
-Three ways to stop X:
- hit ctrl + alt + backspace
- run init 3 or telinit 3
- edit /etc/inittab and reboot
-Three ways to modify X behavior:
- edit /etc/X11/xorg.conf [not recommended]
- run "system-config-display"
- run "Xorg -configure"
-To see the details for X server, run the following cmd:
# xdpyinfo
-Note:
-running X can pose security risk. It can allow another client to access and observe your keystrokes.
-to avoid the above risk:
-use access control using xhost or
-tunnel X over ssh
-X cmd is a symbolic link to Xorg cmd.
-it is good to verify that X Font server is running while X server is running. A simple way to do so:
# service xfs status
-Difference between "startx" and "X"
-startx starts X and also launches the default desktop manager (GNOME).
-When exporting the env var DISPLAY to redirect X output, its set it to the machine where the X server is running.
# DISPLAY=<X server Addr>:0
-Usually this is done from the X client side.-To check if the X client can send its output to remote X servers, run xhost cmd on the X client without parameters.
-Then "xhost +" can be issued to add X servers.
-Default port for X is 6000. If this port is blocked, a workaround is to run ssh with -X option to display X output.
-ssh with -X option is a type of ssh tunneling.
-ssh with a lowercase -x disables the ssh tunneling and is not supposed to be used.
-To troubleshoot ssh:
- use -v or -vvv option
- review /var/log/secure, /var/log/messages
-To switch between desktops edit the foll file:
- /etc/sysconfig/desktop file [which and whatis switchdesk returned null]
-xterm is the standard terminal emulator that runs in X.
Also,
-VNC is a remote desktop sharing system under GPL. However, it is not the same as X.
-For instance, the vnc server and client (called vnc client) are opposite to X server and client.
Learn more about VNC and Linux networking here --> http://timedigit.blogspot.com/2010/09/networking-concepts-linux.html
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