Arch Linux

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,240

[SOLVED] Backlight failure with systemd

For some weeks once kernel 3.14 was released I have had my old Samsung boot initially with a normal screen but once X starts it goes so dim I can barely see the screen. Although the brightness can be restored with the hardware keyboard keys I was trying understand what happened.

Reverting to the kernel 3.13.7-1-ARCH it boots fine and the screen brightness looks normal - however for this kernel I get messages in the systemd journal:

May 02 17:08:49 samsung1 systemd[1]: Starting Load/Save Screen Backlight Brightness of backlight:intel_backlight...
May 02 17:08:49 samsung1 systemd-backlight[191]: Failed to write system attribute: Invalid argument
May 02 17:08:49 samsung1 systemd[1]: systemd-backlight@backlight:intel_backlight.service: main process exited, code=exited, status=1/FAI
May 02 17:08:49 samsung1 systemd[1]: Failed to start Load/Save Screen Backlight Brightness of backlight:intel_backlight.
May 02 17:08:49 samsung1 systemd[1]: Unit systemd-backlight@backlight:intel_backlight.service entered failed state.

Can someone point me to how to diagnose this further?

Thanks

Edit: I have filed upstream at https://bugs.freedesktop.org/show_bug.cgi?id=78200

Last edited by mcloaked (2014-05-07 17:15:55)

---

Mike C

mcloaked

Member

From: Yorkshire, UK

Registered: 2012-02-02

Posts: 1,240

Re: [SOLVED] Backlight failure with systemd

This turned out not a kernel or systemd bug but a somewhat difficult to diagnose issue with a script that I was running during KDE login which set the screen brightness, but when the numerical value of the max-brightness changed during a kernel update this became a problem - but systemd saved the value at shutdown and restored it at next boot which persisted the wrong value of the brightness parameter. I have documented the details in the bug report referenced in the first post.  Using different coding in my script now sets the correct brightness with the new value of max_brightness that appears in /sys/... and the problem has now gone away.

---

Mike C