[K12OSN] Managing screen resolution

Lars Madsen daleif at imf.au.dk
Fri Oct 23 09:00:22 UTC 2009


Gideon Romm wrote:
> Hi, everybody.  I figured I would chime in on forcing video modes.  In
> part, it depends upon what version of LTSP5 you are using, but I will
> talk about things in the most recent sense.  
> 
> Oh, also, anyone using "i810" for an intel card on a modern Linux
> distro, probably shouldn't.  "i810" was abandoned in favor of the
> "intel" driver.  But, that's just a side point.  Also, not that "vesa"
> only has "vesa" modes, so no widescreen options, no matter how much you
> try to force it.  So if its a widescreen resolution you're after, best
> not to use "vesa".
> 
> Now, onto forcing video modes...
> 
> In the latest version of LTSP5, by default, we look towards the video
> drivers' "Xrandr" capabilities to adjust the screen resolution.  For
> those of you unfamiliar with Xrandr, it is a mechanism supported by most
> drivers to adjust video settings on the fly, without restarting the
> Xserver or hardcoding settings in the Xserver configuration file.  To
> wit, there are a set of lts.conf variables prefixed with XRANDR_, such
> as:
> 
> XRANDR_MODE_0 = "1024x768"
> 
> (check the docs for a complete list of XRANDR_ variables for lts.conf)
> 
> So, this is the preferred way of setting the mode.  If Xrandr cannot set
> the specified mode, it will fall back on the driver default, which is
> considerably more graceful than not starting the Xserver at all.
> 
> If you find that you don't get the mode you want with the above setting,
> it may be because the mode cannot be achieved by the driver with the
> auto-detected sync frequencies for the attached monitor.  So, you may
> want to force:
> 
> X_VERTREFRESH = "55-75"
> X_HORZSYNC = "30-100"
> 
> (substituting the above ranges for those for the attached monitor).
> 
> If you still cannot get the mode, you can fall back on not using Xrandr
> at all, and go back to the old way with:
> 
> XRANDR_DISABLE = True
> X_MODE_0 = 1024x768
> 
> If this still does not result in the desired mode, best to get a shell
> on the thin client itself, and look at the thin client's log file
> in /var/log/Xorg.*.log to see why the driver failed to give you the mode
> you requested.
> 
> Hope this helps,
> 
> -Gadi
> 
> PS: Of course, all of the above can be done on a per-workstation basis
> by putting the parameters in the appropriate MAC-address-delineated
> section of your lts.conf file
> 

nice, thanks for this. Had a few problems earlier and didn't know about 
the XRANDR option, will try that later.

/daleif





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