How to Mirror a display to an external Monitor

Solution Verified - Updated -

Environment

  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 5

Issue

  • Need to mirror / clone a laptop monitor to a external monitor.
  • How to clone a laptop display onto a TV and keep the same resolution.

Resolution

Using GNOME's Graphical Display tool

Gnome's Display Dialog can be used to permanently configure the display(s) for a user's session.

  • Run gnome-display-properties by choosing System -> Preferences -> Display

  • Connect the external monitor and configure the settings as desired for multiple displays:

    • Check the "Mirror Screens" box to indicate the screens should be cloned; and choose "Apply":

      selecting the "Mirror Screens" check box and choosing Apply
      (full-image)

    • Choose the one resolution that both monitors should be using; and choose "Apply":

      selecting the single resolution used for both monitors and choosing Apply
      (full-image)

    • Note: Depending on the model of laptop and monitor used, black borders/stretching may be applied if the resolution or aspect ratio does not match the smaller/wider/taller display.

  • Disconnect the monitor and configure the laptop as desired for single monitor use; and choose "Apply".

  • When the external monitor is re-connected, Gnome will assume the user's desired mode during the gnome-session.

  • Disconnecting the external monitor will cause Gnome to return to the single monitor configuration.

Using "xrandr" a command line tool

The xrandr command can be used to temporarily configure the display(s) for a user's session.

  • Open a terminal as the user when in a graphical environment.

  • Run the command below to get the display names:

    $ xrandr
Screen 0: minimum 320 x 200, current 3840 x 1080, maximum 8192 x 8192
LVDS1 connected (normal left inverted right x axis y axis)
   1600x900       60.0*+   40.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9
HDMI3 connected 1920x1080+0+0 (normal left inverted right x axis y axis) 521mm x 293mm
   1920x1080      60.0*+
   1600x1200      60.0  
   1680x1050      59.9  
   1680x945       60.0
   [...]

  • Set the displays so that the external monitor will mirror the current display:

    $ xrandr --output HDMI3 --same-as LVDS1

  • Note: If xrandr leaves the environment in a poor state, then restarting Xorg, changing runlevels, or rebooting should restore the previous configuration.

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