[LightDM] launch xvfb if no monitor detected

[Dave Pawson]

It looks like some combination  of 'headless' (no monitor)
and an install script to answer all the questions?
https://serverfault.com/questions/21255/headless-linux-install

HTH

On Sat, 9 May 2020 at 01:52, Adam Nielsen <a.nielsen at shikadi.net> wrote:
>
> > I am not sure if this is the right mailing list to ask this but I will
> > try. I am creating a Fedora remix for blind and visually impaired users.
> > Some of these users have desktop computers without monitors, because
> > they simply don't need them.
>
> All LightDM does is start X-Windows, so your problem and solution will
> be configuring X-Windows to run without a monitor present.  X has quite
> an extensive configuration so I expect this is possible.  While you're
> working on this, reviewing the X log files will be very helpful to find
> out why it is not starting when expected.  They can be a bit confusing
> to read, but all the answers are there.
>
> > Unfortunately, this causes a problem because the grahpical environment
> > refuses to start at all if no monitor is detected.
>
> This is a a bit surprising but maybe it depends on the video card in
> the system.  Although I have never tried it, I would've expected the
> Linux kernel to create a framebuffer device which is then made
> available to for X to use, with or without a monitor.
>
> So possibly the framebuffer device is not enabled (a reasonable option
> if one does not need a monitor) so enabling this is probably where I
> would start.  You may need to force a display mode through a kernel
> parameter, as I am not sure what the kernel does if it detects no
> monitor present.
>
> Another option is that some drivers like nVidia's closed-source one
> have options to start X without any display devices.  I am not sure
> entirely how they work - I suspect they may report a dummy display
> device that later changes when the monitors are detected, so this could
> be an option too.  Possible drawbacks are that applications may
> misbehave if they try to run with this dummy display (maybe the
> resolution is too small so they crash when calculating widget sizes)
> and of course it requires the users have an nVidia video card in their
> PCs, which is an expense I would certainly forego if I didn't need to
> connect a monitor!
>
> > Do you think that lightdm can somehow solve this? Or should I solve it
> > through some different component?
> >
> > I would like to use xvfb to simulate the monitor.
>
> I think forcing the kernel to use a framebuffer device is probably the
> way to go.  X should detect this and use it with no further
> configuration, in theory at least!
>
> If you see any options relating to ignoring EDID or DDC I suggest they
> be enabled, as this is used to query the presence of a monitor and list
> the resolutions it is capable of, so likely this feature will have to be
> disabled to reliably output a picture with no monitor connected.
>
> Cheers,
> Adam.
> _______________________________________________
> LightDM mailing list
> LightDM at lists.freedesktop.org
> https://lists.freedesktop.org/mailman/listinfo/lightdm



-- 
Dave Pawson
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