This question has been asked many times by many users, but there is no definate answer and it still remains an open bug even after all this time. This appears to be a problem with Ubuntu on some selected number of laptops. I'm using Ubuntu 20.04 for almost 2 years now, but this problem arose in last 1 or 2 months. Most solutions I have read online regarding this are to run an automated script to lower the brightness on every startup. But that is not a native solution. I would like a permanent fix to this because this bug didn't exist for me before 1-2 months ago. My other laptop which is also running 20.04 doesn't have this issue. I'm running the latest version of Ubuntu 20.04 on Dell 5559 laptop with an SSD.
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Both have the same video card and same driver? – David Feb 26 '22 at 16:22
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Both are Dell laptops, but have different hardwares. I have mentioned the one that is having the issue. – Vin Raghav Feb 26 '22 at 16:25
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You pointed out the other one does not have this issue so yes the hardware differences especially the video card do matter. – David Feb 26 '22 at 16:26
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Please see my answer. If it's helpful, please remember to accept it by clicking on the checkmark icon that appears just to the left of my answer. Thanks! – heynnema Feb 26 '22 at 16:54
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Does this answer your question? Full brightness on startup after the recent update – heynnema Feb 26 '22 at 17:06
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See also Brightness is reset to maximum on every restart – ggorlen Jan 26 '23 at 23:51
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The problem is that there's a process that runs at boot, and also at shutdown, that tries to restore/save backlight settings. One some configurations the restore happens incorrectly, and can cause the brightness problem that you see. Here we will add a minor kernel option so that this process doesn't restore an invalid brightness setting.
man systemd-backlight
Rather than using the script that you found, (that I probably wrote), do this:
Edit /etc/default/grub:
sudo -H gedit /etc/default/grub
Locate the line that looks like:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
And change it to:
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash systemd.restore_state=0"
sudo update-grub
Set your brightness to the desired level.
reboot
heynnema
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Could you explain what this will do? Will this impact just the brightness state or everything? – Vin Raghav Feb 27 '22 at 04:33
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@VinRaghav I updated my answer. It's a harmless mod that only effects the brightness being restored to an incorrect value at boot time. – heynnema Feb 27 '22 at 08:02
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@VinRaghav How do you figure? It only effects the backlight restore at boot time. Did you try it? – heynnema Mar 05 '22 at 17:37