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I have the exact same problem on my IdeaPad 520s with an Geforce MX 940.
It happens everytime when I have an active Nvidia card (prime-select
nvidia). With prime-select intel the poweroff/reboot works fine.
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Desktop Bugs,
Status changed to 'Confirmed' because the bug affects multiple users.
** Changed in: gdm3 (Ubuntu)
Status: New => Confirmed
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Desktop Bugs, which is subscribed to gdm3 in Ubuntu.
** Summary changed:
- Cannot shutdown or restart from user session with nvidia drivers via
nvidia-prime installed
+ Cannot shutdown or restart from user session with nvidia drivers in an xorg
session
** Description changed:
Fresh install of 09/07 image on Lenovo y510p laptop GK107M [GeForce