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Old 05-01-2021, 07:09 PM   #1
joboy
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Auto detect monitor resolution possible ?


Hi there,


Please excuse my ignorance, I am running Linux Mint Debian, is there a simple way to auto switch screen resolution, or fallback to VGA when connecting to a monitor not supporting the default resolution like on ms win ? I ask because I am running USB boot for trouble shooting problem and I will boot from any PC old and new, some times the PC only got a basic VGA monitor attached and I got no display due to 'out of range' of the monitor, I know I can modify the boot parameter to boot to VGA, but it would be best if the system can at least fallback to VGA from the default by itself, as far as I remember I could use Ctrl-Alt-BS to switch resolution on some early Linux distro but can no longer now, is there any way to do that ?
 
Old 05-02-2021, 12:57 AM   #2
mrmazda
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Enabling Ctrl-Alt-BS

Simple? Not really. Automagic is supposed to make it so you need do nothing to enjoy a monitor's native mode. It just can't always do so, sometimes the fault of the display, sometimes due to poor or absent support for an old or otherwise uncommon GPU, sometimes due to startup bling an old GPU doesn't support, sometimes a combination.

Have you experienced a failure to fallback often, or just with a particular old display? Are you looking for suitable fallback to happen for a text mode only boot, or for graphical mode only, or both? Are you OK with troubleshooting from a text mode command prompt, mostly just annoyed when you see the out of range message after a GUI tries to start?

Normally, the native resolution of a display is determined, and employed, automatically by both kernel graphics driver and X graphics driver. When out of range occurs it's usually because the monitor's EDID is broken, which can break automatic determination of correct modelines to employ. This seems to be a less frequent problem with flat panel displays. Sometimes the failure is due to an installation to USB that incorporates device specific boot parameters that are inappropriate for other hardware. Sometimes the failure can be worked around by a reboot that includes nomodeset on the kernel command line. vga= though deprecated still works as it used to, until KMS kicks in, which won't happen if nomodeset is a boot parameter. Some UEFI BIOS don't support VESA modes at all, or not properly.

Ctrl-Alt-BS is a dirty exit from graphics mode entirely. IIRC, changing modes via hotkey in graphical mode was either Ctrl-PgUp/PgDn or Ctrl-Alt-PgUp/PgDn. I haven't tried them in years. With most drivers, GUI modes can be changed manually using xrandr or a GUI tool that is xrandr-based.

If you've never tried using Knoppix for rescue booting, you should. It's Debian-based, and expert at making the most of problematic hardware. It includes a lot of help from F2 & F3 screens at its boot menu.

Edit Follows:
Ctrl-Alt-BS is very often disabled in a default installation. Enabling it requires a configuration file either be created, or modified if already existing, either /etc/X11/xorg.conf, or /etc/X11/xorg.conf.d/00-keyboard.conf, containing:
Code:
Section "InputClass"
        Identifier "system-keyboard"
        MatchIsKeyboard "on"
        Option "XkbLayout" "us"
        Option "XkbOptions" "terminate:ctrl_alt_bksp"
EndSection

Last edited by mrmazda; 05-03-2021 at 08:47 PM. Reason: Noticed important omission re Ctrl-Alt-BS
 
Old 05-03-2021, 07:26 PM   #3
joboy
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Quote:
Originally Posted by mrmazda View Post
Simple? Not really. Automagic is supposed to make it so you need do nothing to enjoy a monitor's native mode. It just can't always do so, sometimes the fault of the display, sometimes due to poor or absent support for an old or otherwise uncommon GPU, sometimes due to startup bling an old GPU doesn't support, sometimes a combination.

Have you experienced a failure to fallback often, or just with a particular old display? Are you looking for suitable fallback to happen for a text mode only boot, or for graphical mode only, or both? Are you OK with troubleshooting from a text mode command prompt, mostly just annoyed when you see the out of range message after a GUI tries to start?

Normally, the native resolution of a display is determined, and employed, automatically by both kernel graphics driver and X graphics driver. When out of range occurs it's usually because the monitor's EDID is broken, which can break automatic determination of correct modelines to employ. This seems to be a less frequent problem with flat panel displays. Sometimes the failure is due to an installation to USB that incorporates device specific boot parameters that are inappropriate for other hardware. Sometimes the failure can be worked around by a reboot that includes nomodeset on the kernel command line. vga= though deprecated still works as it used to, until KMS kicks in, which won't happen if nomodeset is a boot parameter. Some UEFI BIOS don't support VESA modes at all, or not properly.

Ctrl-Alt-BS is a dirty exit from graphics mode entirely. IIRC, changing modes via hotkey in graphical mode was either Ctrl-PgUp/PgDn or Ctrl-Alt-PgUp/PgDn. I haven't tried them in years. With most drivers, GUI modes can be changed manually using xrandr or a GUI tool that is xrandr-based.

If you've never tried using Knoppix for rescue booting, you should. It's Debian-based, and expert at making the most of problematic hardware. It includes a lot of help from F2 & F3 screens at its boot menu.

Thanks for the tip, I tried all Ctrl keys combination but none worked, I wished the system automatically fallback to VGA if it found something wrong. You reminded me of Knoppix, I used it long time ago and it worked like magic and came with lot of apps, I wished MINT worked the same way at the booting part.
 
Old 05-03-2021, 08:49 PM   #4
mrmazda
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Quote:
Originally Posted by joboy View Post
I wished MINT worked the same way at the booting part.
Sounds like a reason to think about switching to something else.
 
  


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