vendredi 17 février 2012

Changing the monitor on which the GNOME panels are placed

In my job, it is quite common these days to have a dual display setup on your laptop. Either your are at the office and have a larger LDC monitor, either your are teaching or doing some presentation and you have a beamer projector connected.

With the GNOME 2 desktop, the UI is based on 2 toolbars (called "panels") on top and bottom of the screen, that are very handy for launching common apps. With two screens, what happens is that these panels are usually placed on one screen, where you would rather have them on the other one.

The desktop provides a graphical way to move them around with the mouse, by holding the "alt" key down, and moving them around. But this is rather difficult in some lighting situations, when the projector image is bad and you hardly see your mouse pointer. Worse, you might end up with a vertical panel, and then, due to the lack of free space in the panel to click on, you're doomed to use either the graphical editor, either the command line tool.

The other solution is to edit this item directly in the gnome registry. Oh, sorry, I know, GNOME has no registry, only Windows has... Although it can look quite similar as viewed from the corresponding graphical editors, the implementation beneath is completely different. While Windows stores all its configuration information in two HUGE files, on Linux the information is spread over many many files, usually under /etc. It's only the way the information is displayed that makes it look like Windows registry (a tree of pairs key/values). And it is called GConf repository instead of registry.

For the desktops panels, the items to consider are stored under the keys /apps/panel/toplevels/ keys, one is called bottom_panel_screen0, the other top_panel_screen0 (at least on my computer, check on yours).

This can be done graphically with the gconf-editor tool, but when you have the audience waiting, it can be complicated finding and clicking on correct items... The best idea is to use the command-line tool provided, and to have somewhere two scripts, one for switching panels to monitor 0, one for switching to monitor 1.

So just copy/paste these lines in two files that you store whereyouwant, and add two symlinks on them on your desktop. Then, once you are in front of the audience and you have trouble with the panels, just reduce all the opened windows and double-click on one of the links. Changes should apply in less than a second.

#! /bin/bash
# switch top/bottom panels to screen 0
gconftool-2 --set "/apps/panel/toplevels/bottom_panel_screen0/monitor" --type int 0
gconftool-2 --set "/apps/panel/toplevels/top_panel_screen0/monitor" --type int 0

#! /bin/bash
# switch top/bottom panels to screen 1
gconftool-2 --set "/apps/panel/toplevels/bottom_panel_screen0/monitor" --type int 1
gconftool-2 --set "/apps/panel/toplevels/top_panel_screen0/monitor" --type int 1

To create the symlinks (remember to adjust the path to where you put the files), just "cd" to your desktop folder ($HOME/Desktop usually) and type:
>ln -s $HOME/scripts/screen/ panel_0
>ln -s $HOME/scripts/screen/ panel_1

And don't forget to make your files executable! (chmod)

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