I just disabled the GDM service to use QT programs and mplayer output. And I need to change HDMI output resolution of my Angstrom distro and it should be on-the-fly. That means basically doing this without GDM-X11:

xrandr --output HDMI-0 --mode 720x480 --rate 60

There are a thousands of samples of doing this with xrandr, but I couldn't find any without it.

  • Why you can't do this with xrandr ? – SHW Sep 10 '15 at 7:17
  • Actually i can, but i'm not going to use GDM in my application. So, i have to do this without X11. – Ceyhan ILERI Sep 10 '15 at 7:33

You seem to be confused about what gdm and x11 do.

The X server uses the X11 protocol to allow applications to use graphical hardware and input devices. It allows them to draw windows on the screen, perform certain operations on those windows, react to user input events, and close the windows again. GDM is one such application. As far as the X server is concerned, it is not a special application. It allows users to log on, but the X server has no concept of users and passwords, it just knows about applications.

It is perfectly possible to use the X server without GDM or another display manager. If you do that, you still need to configure the X server, and doing that is done with the same programs as when you do use GDM (i.e., xrandr and others). Alternatively, you may also be using the framebuffer, in which case configuration is done through other means. However, as this is somewhat more involved and not as efficient (since the X server has better drivers for'most display hardware than the kernel framebuffer), I would recommend against it.

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  • Yeah, I was confused about them but you kinda explained them. I've tried to use framebuffer but it was not efficient as much as I want, then I tried to do it by using X server. And basically, i can use X server even if I disable GDM, right? But when i disable GDM service, doesn't it kill the X processes? Do I need to reconfigure them anyway? Sorry about that kinda confusing questions, and really appreciate for your help! – Ceyhan ILERI Sep 10 '15 at 11:07
  • You want to use "startx", presumably. This starts an X server and a default window manager. – Wouter Verhelst Sep 10 '15 at 11:46

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