screen brightness slider has no effect

Asked by Kevin Leeds on 2016-02-13

f.lux also has no effect.
also when i try to do
 sudo echo 50 > /sys/class/backlight/acpi_video0/brightness
then it says 'bash: brightness: permission denied'.

Trusty Tahr 14.04 updated to current

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Kevin Leeds
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This question was originally filed as bug #1545264.

sudo echo 50 > /sys/class/backlight/acpi_video0/brightness

Doesn't work because the only part of the command with sudo access is the echo part. Sudo doesn't traverse the redirection. If you want it to work then use:

echo 50 | sudo tee /sys/class/backlight/acpi_video0/brightness

Here, the echo part runs as user but is piped to tee which has been ran with sudo so has full access..

It's a common rookie mistake

Kevin Leeds (knleeds) said : #3

Thank you for the important information regarding Tee!
I guess I'm not too old to be a rookie.
It still has no effect on the brightness, however.
I have dual monitors. It may be caused by my the fact they're DisplayPort and not DVI plugs, but they're DVI monitors, so I have two identical adaptors attached, that seem good quality. I have no idea if it's relevant. Thank you!

Kevin Leeds (knleeds) said : #4

(Also, how can I report my dual monitor config to you for better diagnosis?)

Kevin Leeds (knleeds) said : #5

I have tried different numbers 15, 5, 1, 0 and still the monitor remains apparently the same brightness. The idea is supposed to be not to fully wake me up since it's nighttime.

What is the output of:

sudo dmidecode -t 1; lsb_release -a; uname -a


Kevin Leeds (knleeds) said : #7

# dmidecode 2.12
SMBIOS 2.7 present.

Handle 0x0001, DMI type 1, 27 bytes
System Information
 Manufacturer: Dell Inc.
 Product Name: OptiPlex 7010
 Version: 01
 Serial Number: 2S2QT02
 UUID: 4C4C4544-0053-3210-8051-B2C04F543032
 Wake-up Type: Power Switch
 SKU Number: OptiPlex 7010
 Family: Not Specified

No LSB modules are available.
Distributor ID: Ubuntu
Description: Ubuntu 14.04.3 LTS
Release: 14.04
Codename: trusty
Linux kevin-desktop 3.19.0-49-generic #55~14.04.1-Ubuntu SMP Fri Jan 22 11:24:31 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

Wait, if you have reported a bug then you don't need a question as well and all conversations regarding the bug should happen in one place, on the bug report.