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Using intel video drivers with kms and i915 on arch linux I haven't been able to start Xorg in a different tty than from the calling one logged as root. By example:

Logged as root on tty1

X vt7 :0

Freezes the PC and within the Xorg.0.log I see

intel(0): failed to set mode: Permission denied [13]

In the other hand

Logged as root on tty1

X vt1 :0

Everything works as usual

I know is not really a serious problem since I still can use Xorg but I'm really intrigued about this behavior for two main reasons

  1. permissions for all tty1 ... tty49 are cwr-w----- root tty
  2. even if a I'm logged in both tty1 and tty2 with root and try to start X server on tty2 from tty1 it doesn't work as if it only had permission for the calling tty

Does anyone have and idea on what's going on?

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You were on the right track. This has indeed something to do with KMS. For video drivers that supports KMS X can be set up to run as a non-root user. You can check if your X is run as a non-root user in the way: How to determine if X server runs with root privileges. To strengthen my point, I quote directly from the Arch Linux homepage:

"xorg-server 1.16 is now available 2014-07-28

  • The new version comes with the following changes: X is now rootless with the help of systemd-logind, this also means that it must be launched from the same virtual terminal as was used to log in, redirecting stderr also breaks rootless login. The old root execution behavior can be restored through the Xorg.wrap config file (man xorg.wrap). Please note that launching X through a login-manager (gdm, kdm, ...) doesn't yet provide rootless access.
  • The default configuration files are now in /usr/share/X11/xorg.conf.d, all host configurations are still taking place in /etc/X11/xorg.conf ..."

It's generally a good idea to either read the update messages after running pacman -Syu or subscribing to the arch-announce mailing list which you can do here and check the website https://www.archlinux.org/ first.

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