blctl - backlight control utility
blctl [OPTION]... [BRIGTHNESS]
blctl controls backlight settings using the /sys/class/backlight interface of the Linux kernel. It supports changing brightness in a configurable number of steps, as well as powering the backlight on and off on devices that support power control over the backlight interface.
Brightness
Control
The brightness setting is administered using the
BRIGHTNESS argument, which may be one of:
|
min |
Minimal brightness. |
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max |
Maximal brightness. |
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inc |
Step increment. |
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dec |
Step decrement. |
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sN |
Step setting to step #N (range 0..CNT-1). |
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VALUE |
Brightness value (range MIN..MAX). |
Minimal and maximal values default to HW minimum/maximum and may be adjusted with the -m MIN and -M MAX options or in the configuration file. The values of MIN, MAX, and BRIGHTNESS may also be specified as floating-point values (0.0 to 1.0) or percentages (0% to 100%) for proportional setting from the corresponding range (e.g., -M 0.9 sets maximal brightness to 90% of HW maximum, -m 0.1 sets minimal brightness to 10% of maximal brightness, and using 0.5 as BRIGHTNESS sets brightness to the middle of the range between MIN and MAX).
Step adjustment using inc/dec and sN requires the step count to be set with the -s option or in the configuration file. If the -r option is given, the step adjustment with inc/dec cycles through all available steps.
Power
Control
Power control is available only on devices where the
backlight driver allows turning the backlight on and off by
writing numeric values into the bl_power file under
/sys/class/backlight/IFC. The Linux kernel uses the
value of 0 for power-on and 4 for power-off;
however, some drivers may use different values (e.g.,
0 for power-on and 1 for power-off). The
power-on and power-off values used by blctl may be
adjusted using the -O and -o options or in the
configuration file.
Backlight power control is administered with the -p PWR option, where PWR may be one of:
|
on |
Turn the backlight on. |
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off |
Turn the backlight off. |
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toggle |
Toggle between on and off. |
Options without arguments may be concatenated after a single hyphen. Space between an option and its argument may be omitted.
|
-c CFG |
Use configuration file CFG. | ||
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-h |
Output usage information. | ||
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-i IFC |
Use the backlight interface /sys/class/backlight/IFC. | ||
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-m MIN |
Minimal brightness (range 0..MAX, default 0). | ||
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-M MAX |
Maximal brightness (range 0..HW maximum, default: HW maximum). | ||
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-o OFF |
Power-off value for bl_power (default: 4). | ||
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-O ON |
Power-on value for bl_power (default: 0). | ||
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-p PWR |
Power setting (range 0..4 or one of on/off/toggle). | ||
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-r |
Recurring brightness step adjustment. | ||
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-s CNT |
Step count for step brightness setting. | ||
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-v |
Output verbose information. |
The
configuration file consists of option=value
lines. Leading and trailing whitespaces and any text after
the # symbol are ignored. Boolean values can be either
on, yes, or true for true (enabled) or
off, no, or false for false (disabled).
Recognized configuration options are:
iface=IFC
Backlight interface selection (equivalent to -i).
max=MAX
Maximal brightness value (equivalent to -M).
min=MIN
Minimal brightness value (equivalent to -m).
power-on=ON
On value for power control (equivalent to -O).
power-off=OFF
Off value for power control (equivalent to -o).
recur=boolean
Recurring step adjustment (equivalent to -r).
steps=CNT
Step count for step brightness adjustment (equivalent to -s).
Configuration options are ignored if the corresponding command line options are used.
Copyright (c)
2025 Vic B <vic@4ever.vip>.
License GPLv3: GNU GPL version 3
<https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and
redistribute it.
There is NO WARRANTY, to the extent permitted by
law.