Not fully supported graphics card

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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:

1. Boot into single user mode
2. Use command 'Xorg -configure' to create a 'xorg.conf.new' file in '/root' folder.
3. If old graphics were working fine then take backup of '/etc/X11/xorg.conf' file appropriately.
4. Replace '/etc/X11/xorg.conf' file with newly generated 'xorg.conf.new' file and restart the machine in run level 5.
5. If things do not work then restart in single mode and edit the '/etc/X11/xorg.conf' file and replace all Driver lines with 'Driver "vesa"'
6. 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 'xrandr' and 'cvt' commands to add more modes.

Display all connected devices

To see all connected devices use:

xrandr --verbose

command. This will list all the connected devices and their recognized supported modes. This can also be done using GUI accessible at "System -> Preferences -> Display (gnome-display-properties)".

Creating new mode

To create a new mode first a mode-line needs to be constructed. Use:

cvt <width> <height>

For example,

cvt 800 600

This will result into a mode-line. Now a mode can be created with the mode-line output using

xrandr --newmode <MODE-LINE>

For example if the output of 'cvt 800 600' command is:

Modeline "800x600_60.00"   38.25  800 832 912 1024  600 603 607 624 -hsync +vsync

then use:

xrandr --newmode "800x600_60.00"   38.25  800 832 912 1024  600 603 607 624 -hsync +vsync

to create the new mode. Verify using 'xrandr --verbose' 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:

xrandr --addmode <device> <mode>

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

Choosing a mode for display

To choose a mode for display once mode has been added one can use 'gnome-display-properties' or System -> Preferences -> Display menu option. Howover if use of command-line is preferred then command:

xrandr --output <device> --mode <mode>

can be used to change the mode using command line.

More information on configuring xrandr can be learned from https://wiki.ubuntu.com/X/Config/Resolution

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