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=Not fully supported graphics card=

Sometimes one may purchase a new graphics card or complete system where graphics card is not supported by installed OS. In such cases one can install Cent-OS by choosing "Generic display driver" called vesa. To use generic display driver on a already running machine use following steps:
#Boot into single user mode
#Use command '<tt>Xorg -configure</tt>' to create a '<tt>xorg.conf.new</tt>' file in '<tt>/root</tt>' folder.
#If old graphics were working fine then take backup of '<tt>/etc/X11/xorg.conf</tt>' file appropriately.
#Replace '<tt>/etc/X11/xorg.conf</tt>' file with newly generated '<tt>xorg.conf.new</tt>' file and restart the machine in run level 5.
#If things do not work then restart in single mode and edit the '<tt>/etc/X11/xorg.conf</tt>' file and replace all Driver lines with 'Driver "vesa"'
#Again restart the machine and check if things work fine.



==Adding more display modes==

Sometimes Linux may not recognize all the different display modes that are supported by a Graphics Card. For example at time of this writing Cent-OS 6.3 recognizes only 1600x900 resolution on Dell latitude E6430 laptops with Intel HD Graphics 4000 on-board graphics card. To add more modes one can use '<tt>xrandr</tt>' and '<tt>cvt</tt>' commands to add more modes.


===Display all connected devices===

To see all connected devices use:
<pre>
xrandr --verbose
</pre>
command. This will list all the connected devices and their recognized supported modes. This can also be done using GUI accessible at "System -&gt; Preferences -&gt; Display (gnome-display-properties)". 


===Creating new mode===

To create a new mode first a mode-line needs to be constructed. Use:
<pre>
cvt <width> <height>
</pre>
For example,
<pre>
cvt 800 600
</pre>

This will result into a mode-line. Now a mode can be created with the mode-line output using
<pre>
xrandr --newmode <MODE-LINE>
</pre>

For example if the output of '<tt>cvt 800 600</tt>' command is:
<pre>
Modeline "800x600_60.00"   38.25  800 832 912 1024  600 603 607 624 -hsync +vsync
</pre>
then use:
<pre>
xrandr --newmode "800x600_60.00"   38.25  800 832 912 1024  600 603 607 624 -hsync +vsync
</pre>
to create the new mode. Verify using '<tt>xrandr --verbose</tt>' that new mode is created.

Now once a mode is created, it has to be added to the list of possible options for a given display using:
<pre>
xrandr --addmode <device> <mode>
</pre>

The device name is available in the '<tt>xrandr --verbose</tt>' output as '<tt>XYZ connected</tt>'. Typical device names are default, VGA, LVDS etc. Mode name is above case is "800x600_60.00". Mode names are also listed in '<tt>xrandr --verbose</tt>' output.


==Choosing a mode for display==

To choose a mode for display once mode has been added one can use '<tt>gnome-display-properties</tr>' or System -&gt; Preferences -&gt; Display menu option. Howover if use of command-line is preferred then command:
<pre>
xrandr --output <device> --mode <mode>
</pre>
can be used to change the mode using command line.