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Re: [K12OSN] Managing screen resolution



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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