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light is not working withough root #48623

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rokk4 opened this issue Oct 17, 2018 · 13 comments
Closed

light is not working withough root #48623

rokk4 opened this issue Oct 17, 2018 · 13 comments

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@rokk4
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rokk4 commented Oct 17, 2018 •
edited

Issue description

Since a few days, around the 14th october, light is not working without root.
Using sudo light -S works fine.
Since #nixos didn't know any further answers, I opened this issue.

Steps to reproduce

/etc/nixos/configuration.nix
programs.light.enable = true;

Technical details

Please run nix-shell -p nix-info --run "nix-info -m" and paste the
results.

  nix-info -m

 - system: `"x86_64-linux"`
 - host os: `Linux 4.18.13, NixOS, 19.03pre155123.32bcd72bf28 (Koi)`
 - multi-user?: `yes`
 - sandbox: `yes`
 - version: `nix-env (Nix) 2.1.3`
 - channels(rokka): `"nixpkgs-19.03pre151875.7c1b85cf6de"`
 - channels(root): `"nixos-19.03pre155123.32bcd72bf28, nixpkgs-19.03pre154774.cefd0f7e86b"`
 - nixpkgs: `/home/rokka/.nix-defexpr/channels/nixpkgs`

[rokka@derGeraet:~]$ nixos-option programs.light.enable
Value:
true

Default:
false

Example:


Description:

"Whether to install Light backlight control with setuid wrapper.\n"

Declared by:
  "/home/rokka/.nix-defexpr/channels/nixpkgs/nixos/modules/programs/light.nix"

Defined by:
  "/etc/nixos/configuration.nix"

[rokka@derGeraet:~]$ nixos-option security.wrappers.light.source
This attribute set contains:

Yes, this is the full output of nixos-option security.wrappers.light.source

[rokka@derGeraet:~]$ sudo ls /run/wrappers/bin/light
[sudo] password for rokka:
ls: cannot access '/run/wrappers/bin/light': No such file or directory

[rokka@derGeraet:~]$ ls /run/wrappers/bin/
dbus-daemon-launch-helper       newgidmap       passwd       polkit-agent-helper-1       sudoedit
dbus-daemon-launch-helper.real  newgidmap.real  passwd.real  polkit-agent-helper-1.real  sudoedit.real
fusermount                      newgrp          ping         sg                          sudo.real
fusermount3                     newgrp.real     ping.real    sg.real                     su.real
fusermount3.real                newuidmap       pkexec       su                          unix_chkpwd
fusermount.real                 newuidmap.real  pkexec.real  sudo                        unix_chkpwd.real

[rokka@derGeraet:~]$ which light
/run/current-system/sw/bin/light

[rokka@derGeraet:~]$ sudo grep light /run/current-system/activate
[sudo] password for rokka:

yes, it has no output at all
@xaverdh
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xaverdh commented Oct 17, 2018 •
edited

As a workaround I suggest doing (as per https://haikarainen.github.io/light/):

services.udev.extraRules = ''
ACTION=="add", SUBSYSTEM=="backlight", RUN+="${pkgs.coreutils}/bin/chgrp video %S%p/brightness", RUN+="${pkgs.coreutils}/bin/chmod g+w %S%p/brightness"
'';

services.udev.path = [
pkgs.coreutils # for chgrp
];

then add your user account to the video group (users.extraUsers.<name>.extraGroups) and add light to your systemPackages instead of setting programs.light.enable.

@dtzWill
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dtzWill commented Oct 18, 2018

Hmm do you have #47544 in the commit you're using? It does those things for you, and should have different text in nixos-option. Try updating I suppose, and please report if any of that is needed beyond enabling and adding yourself to the group.

@emmanuelrosa
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I'm encountering the same issue.

For some reason light is not getting wrapped when programs.light.enable = true. I've narrowed it down to missing code in the activation script. The activation script is supposed to contain a chunk of code that looks something like this:

cp /nix/store/*-security-wrapper/bin/security-wrapper $wrapperDir/light
echo -n "/nix/store/*-light-*/bin/light" > $wrapperDir/light.real

# Prevent races
chmod 0000 $wrapperDir/light
chown root.nogroup $wrapperDir/light

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/light

However, said chunk of code is missing. Here's my activation script (NixOS Loris, commit 777e94d):

#! /nix/store/cinw572b38aln37glr0zb8lxwrgaffl4-bash-4.4-p23/bin/bash

systemConfig=/nix/store/v49n276ycj9kwcyqpr76inqmbjscy523-nixos-system-nixos-laptop-19.09.git.777e94d

export PATH=/empty
for i in /nix/store/d9s1kq1bnwqgxwcvv4zrc36ysnxg8gv7-coreutils-8.30 /nix/store/wnjv27b3j6jfdl0968xpcymlc7chpqil-gnugrep-3.3 /nix/store/krhqmaqal0gklh15rs2bwrqzz8mg9lrn-findutils-4.6.0 /nix/store/1dppisyngjln0m2fzvyzh0gj9wf9i12x-getent-1003.1-2008 /nix/store/f5wl80zkrd3fc1jxsljmnpn7y02lz6v1-glibc-2.27-bin /nix/store/hciblqqf5fwasmiac3ciw30h574nf6kk-shadow-4.6 /nix/store/zmbhwb6l8nvqsxligbsvxm99jbbnbx70-net-tools-1.60_p20170221182432 /nix/store/96jfbs5vj01fiiz6s81wzfvrxhdx0rm5-util-linux-2.33.1-bin; do
    PATH=$PATH:$i/bin:$i/sbin
done

_status=0
trap "_status=1 _localstatus=\$?" ERR

# Ensure a consistent umask.
umask 0022

#### Activation script snippet stdio:
_localstatus=0


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "stdio" "$_localstatus"
fi

#### Activation script snippet binsh:
_localstatus=0
# Create the required /bin/sh symlink; otherwise lots of things
# (notably the system() function) won't work.
mkdir -m 0755 -p /bin
ln -sfn "/nix/store/mcyvp1s45scjkkhyb1m16aqlsb8wr6hs-bash-interactive-4.4-p23/bin/sh" /bin/.sh.tmp
mv /bin/.sh.tmp /bin/sh # atomically replace /bin/sh


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "binsh" "$_localstatus"
fi

#### Activation script snippet domain:
_localstatus=0


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "domain" "$_localstatus"
fi

#### Activation script snippet users:
_localstatus=0
install -m 0700 -d /root
install -m 0755 -d /home

/nix/store/kiapz3kjvb46jbvswdjkmrzg0s4l2zm7-perl-5.28.1/bin/perl -w \
  -I/nix/store/rf4q26ivs49mm45cxgjj35knl08gkx8p-perl5.28.1-File-Slurp-9999.25/lib/perl5/site_perl \
  -I/nix/store/b92bmz80n5pj5k50x32bfr97p3d60zyf-perl5.28.1-JSON-4.00/lib/perl5/site_perl \
  /nix/store/1hkp2n6hz3ybf2rvkjkwrzgbjkrrakzl-update-users-groups.pl /nix/store/s5bs9c487fv77dh3b8kkamr242gqjiqz-users-groups.json


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "users" "$_localstatus"
fi

#### Activation script snippet groups:
_localstatus=0


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "groups" "$_localstatus"
fi

#### Activation script snippet etc:
_localstatus=0
# Set up the statically computed bits of /etc.
echo "setting up /etc..."
/nix/store/kiapz3kjvb46jbvswdjkmrzg0s4l2zm7-perl-5.28.1/bin/perl -I/nix/store/rf4q26ivs49mm45cxgjj35knl08gkx8p-perl5.28.1-File-Slurp-9999.25/lib/perl5/site_perl /nix/store/vn1xs9s2akf79y1pbya2qldydbf2b22m-setup-etc.pl /nix/store/vjib1rlgaznvvqrwmlq3kh139p4r46h1-etc/etc


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "etc" "$_localstatus"
fi

#### Activation script snippet hostname:
_localstatus=0
hostname "nixos-laptop"


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "hostname" "$_localstatus"
fi

#### Activation script snippet specialfs:
_localstatus=0
specialMount() {
  local device="$1"
  local mountPoint="$2"
  local options="$3"
  local fsType="$4"

  if mountpoint -q "$mountPoint"; then
    local options="remount,$options"
  else
    mkdir -m 0755 -p "$mountPoint"
  fi
  mount -t "$fsType" -o "$options" "$device" "$mountPoint"
}
source /nix/store/4pprvrkcfsc560b6v72raymy0f0ziiw6-mounts.sh


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "specialfs" "$_localstatus"
fi

#### Activation script snippet modprobe:
_localstatus=0
# Allow the kernel to find our wrapped modprobe (which searches
# in the right location in the Nix store for kernel modules).
# We need this when the kernel (or some module) auto-loads a
# module.
echo /nix/store/9p1j0gh1z3gahl1nvg637f96yb7djyg2-kmod-25/bin/modprobe > /proc/sys/kernel/modprobe


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "modprobe" "$_localstatus"
fi

#### Activation script snippet nix:
_localstatus=0
# Nix initialisation.
install -m 0755 -d \
  /nix/var/nix/gcroots \
  /nix/var/nix/temproots \
  /nix/var/nix/userpool \
  /nix/var/nix/profiles \
  /nix/var/nix/db \
  /nix/var/log/nix/drvs
install -m 1777 -d \
  /nix/var/nix/gcroots/per-user \
  /nix/var/nix/profiles/per-user \
  /nix/var/nix/gcroots/tmp


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "nix" "$_localstatus"
fi

#### Activation script snippet var:
_localstatus=0
# Various log/runtime directories.

mkdir -m 1777 -p /var/tmp

# Empty, immutable home directory of many system accounts.
mkdir -p /var/empty
# Make sure it's really empty
/nix/store/qzrrw4ycnsj99488xv1v2rwmmjf3q9wr-e2fsprogs-1.44.5-bin/bin/chattr -f -i /var/empty || true
find /var/empty -mindepth 1 -delete
chmod 0555 /var/empty
chown root:root /var/empty
/nix/store/qzrrw4ycnsj99488xv1v2rwmmjf3q9wr-e2fsprogs-1.44.5-bin/bin/chattr -f +i /var/empty || true


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "var" "$_localstatus"
fi

#### Activation script snippet resolvconf:
_localstatus=0
# Systemd resolved controls its own resolv.conf
rm -f /run/resolvconf/interfaces/systemd


# Make sure resolv.conf is up to date if not managed manually or by systemd
/nix/store/288qfr48xix808jiz676sfxwdc8ppjp5-openresolv-3.9.0/bin/resolvconf -u



if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "resolvconf" "$_localstatus"
fi

#### Activation script snippet udevd:
_localstatus=0
# The deprecated hotplug uevent helper is not used anymore
if [ -e /proc/sys/kernel/hotplug ]; then
  echo "" > /proc/sys/kernel/hotplug
fi

# Allow the kernel to find our firmware.
if [ -e /sys/module/firmware_class/parameters/path ]; then
  echo -n "/nix/store/l520474vfisll1z5hv60aa5h163072hl-firmware/lib/firmware" > /sys/module/firmware_class/parameters/path
fi


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "udevd" "$_localstatus"
fi

#### Activation script snippet udisks2:
_localstatus=0
mkdir -m 0755 -p /var/lib/udisks2


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "udisks2" "$_localstatus"
fi

#### Activation script snippet usrbinenv:
_localstatus=0
mkdir -m 0755 -p /usr/bin
ln -sfn /nix/store/d9s1kq1bnwqgxwcvv4zrc36ysnxg8gv7-coreutils-8.30/bin/env /usr/bin/.env.tmp
mv /usr/bin/.env.tmp /usr/bin/env # atomically replace /usr/bin/env


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "usrbinenv" "$_localstatus"
fi

#### Activation script snippet wrappers:
_localstatus=0
# Look in the system path and in the default profile for
# programs to be wrapped.
WRAPPER_PATH=/nix/store/z3hhfzm5w7nniy9d19v2yp342mjbmfnj-system-path/bin:/nix/store/z3hhfzm5w7nniy9d19v2yp342mjbmfnj-system-path/sbin

# We want to place the tmpdirs for the wrappers to the parent dir.
wrapperDir=$(mktemp --directory --tmpdir="/run/wrappers" wrappers.XXXXXXXXXX)
chmod a+rx $wrapperDir

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/dbus-daemon-launch-helper
echo -n "/nix/store/vf3kimm17wqbs63zh5kz85q114q28p0z-dbus-1.12.12/libexec/dbus-daemon-launch-helper" > $wrapperDir/dbus-daemon-launch-helper.real

# Prevent races
chmod 0000 $wrapperDir/dbus-daemon-launch-helper
chown root.messagebus $wrapperDir/dbus-daemon-launch-helper

chmod "u+s,g-s,u+rx,g+rx,o-rx" $wrapperDir/dbus-daemon-launch-helper

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/fusermount
echo -n "/nix/store/0rz1lb2lmx250ga94y9zrffzwgh1qx9s-fuse-2.9.9/bin/fusermount" > $wrapperDir/fusermount.real

# Prevent races
chmod 0000 $wrapperDir/fusermount
chown root.root $wrapperDir/fusermount

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/fusermount

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/fusermount3
echo -n "/nix/store/47yj0mrlx5ybslpfyi7js9v3hgpmwznx-fuse-3.4.1/bin/fusermount3" > $wrapperDir/fusermount3.real

# Prevent races
chmod 0000 $wrapperDir/fusermount3
chown root.root $wrapperDir/fusermount3

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/fusermount3

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/newgidmap
echo -n "/nix/store/hciblqqf5fwasmiac3ciw30h574nf6kk-shadow-4.6/bin/newgidmap" > $wrapperDir/newgidmap.real

# Prevent races
chmod 0000 $wrapperDir/newgidmap
chown root.root $wrapperDir/newgidmap

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/newgidmap

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/newgrp
echo -n "/nix/store/hciblqqf5fwasmiac3ciw30h574nf6kk-shadow-4.6/bin/newgrp" > $wrapperDir/newgrp.real

# Prevent races
chmod 0000 $wrapperDir/newgrp
chown root.root $wrapperDir/newgrp

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/newgrp

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/newuidmap
echo -n "/nix/store/hciblqqf5fwasmiac3ciw30h574nf6kk-shadow-4.6/bin/newuidmap" > $wrapperDir/newuidmap.real

# Prevent races
chmod 0000 $wrapperDir/newuidmap
chown root.root $wrapperDir/newuidmap

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/newuidmap

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/passwd
echo -n "/nix/store/hciblqqf5fwasmiac3ciw30h574nf6kk-shadow-4.6/bin/passwd" > $wrapperDir/passwd.real

# Prevent races
chmod 0000 $wrapperDir/passwd
chown root.root $wrapperDir/passwd

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/passwd

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/ping
echo -n "/nix/store/22nfcbw7n7yd87yql537pma23h47bfzz-iputils-20180629/bin/ping" > $wrapperDir/ping.real

# Prevent races
chmod 0000 $wrapperDir/ping
chown root.root $wrapperDir/ping

# Set desired capabilities on the file plus cap_setpcap so
# the wrapper program can elevate the capabilities set on
# its file into the Ambient set.
/nix/store/22qfvavs0hmg1vh2jwh0cal7apj0g0x0-libcap-2.26/bin/setcap "cap_setpcap,cap_net_raw+p" $wrapperDir/ping

# Set the executable bit
chmod u+rx,g+x,o+x $wrapperDir/ping

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/pkexec
echo -n "/nix/store/g5r63nlmlzn8n6v7ahrfii0b5pk55lar-polkit-0.115-bin/bin/pkexec" > $wrapperDir/pkexec.real

# Prevent races
chmod 0000 $wrapperDir/pkexec
chown root.root $wrapperDir/pkexec

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/pkexec

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/polkit-agent-helper-1
echo -n "/nix/store/r1b8ggg8w9kmdv9fjrir17qxbh1p38sj-polkit-0.115/lib/polkit-1/polkit-agent-helper-1" > $wrapperDir/polkit-agent-helper-1.real

# Prevent races
chmod 0000 $wrapperDir/polkit-agent-helper-1
chown root.root $wrapperDir/polkit-agent-helper-1

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/polkit-agent-helper-1

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/sg
echo -n "/nix/store/hciblqqf5fwasmiac3ciw30h574nf6kk-shadow-4.6/bin/sg" > $wrapperDir/sg.real

# Prevent races
chmod 0000 $wrapperDir/sg
chown root.root $wrapperDir/sg

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/sg

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/su
echo -n "/nix/store/c4w7l847prnan6zzhx718c788bdkrg02-shadow-4.6-su/bin/su" > $wrapperDir/su.real

# Prevent races
chmod 0000 $wrapperDir/su
chown root.root $wrapperDir/su

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/su

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/sudo
echo -n "/nix/store/nik1ylfpjy80pi7qq0llvv7r359bq9s9-sudo-1.8.27/bin/sudo" > $wrapperDir/sudo.real

# Prevent races
chmod 0000 $wrapperDir/sudo
chown root.root $wrapperDir/sudo

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/sudo

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/sudoedit
echo -n "/nix/store/nik1ylfpjy80pi7qq0llvv7r359bq9s9-sudo-1.8.27/bin/sudoedit" > $wrapperDir/sudoedit.real

# Prevent races
chmod 0000 $wrapperDir/sudoedit
chown root.root $wrapperDir/sudoedit

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/sudoedit

cp /nix/store/r49crjh43kjiis3pvbkb1562innv1j9v-security-wrapper/bin/security-wrapper $wrapperDir/unix_chkpwd
echo -n "/nix/store/wm300mkfk9sfx2lv3rcblqm8bza673g0-linux-pam-1.3.0/sbin/unix_chkpwd.orig" > $wrapperDir/unix_chkpwd.real

# Prevent races
chmod 0000 $wrapperDir/unix_chkpwd
chown root.nogroup $wrapperDir/unix_chkpwd

chmod "u+s,g-s,u+rx,g+x,o+x" $wrapperDir/unix_chkpwd


if [ -L /run/wrappers/bin ]; then
  # Atomically replace the symlink
  # See https://axialcorps.com/2013/07/03/atomically-replacing-files-and-directories/
  old=$(readlink -f /run/wrappers/bin)
  ln --symbolic --force --no-dereference $wrapperDir /run/wrappers/bin-tmp
  mv --no-target-directory /run/wrappers/bin-tmp /run/wrappers/bin
  rm --force --recursive $old
else
  # For initial setup
  ln --symbolic $wrapperDir /run/wrappers/bin
fi


if (( _localstatus > 0 )); then
  printf "Activation script snippet '%s' failed (%s)\n" "wrappers" "$_localstatus"
fi


# Make this configuration the current configuration.
# The readlink is there to ensure that when $systemConfig = /system
# (which is a symlink to the store), /run/current-system is still
# used as a garbage collection root.
ln -sfn "$(readlink -f "$systemConfig")" /run/current-system

# Prevent the current configuration from being garbage-collected.
ln -sfn /run/current-system /nix/var/nix/gcroots/current-system

exit $_status

@dtzWill
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dtzWill commented Mar 11, 2019 via email

@emmanuelrosa
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Thank you @dtzWill

Adding myself to the video group worked 👍

@xaverdh
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xaverdh commented Mar 11, 2019

Good, that udev rule is now set up!
I guess this can be closed now?

@dtzWill
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dtzWill commented Mar 11, 2019

Sounds like it, yes!

@dtzWill dtzWill closed this as completed Mar 11, 2019
@asheshambasta
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asheshambasta commented May 12, 2019 •
edited

Adding myself to the video group doesn't seem to do the trick.

Here's the user data:

# Create the video group (I've added this line after just adding the user to the video group)
users.groups.video = {}; 

users.users.ashesh = { 
  isNormalUser = true;
  extraGroups = [ "wheel" "video" ]; 
}

Doing light -U 10 has no effect whatsoever, and just a blank-line is output to stdout.

Scratch that, I was doing something silly.

@rjpcasalino
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rjpcasalino commented Aug 1, 2019 •
edited

Sorry, I know the issue is closed but I was wondering if it'd be worth it to update https://nixos.wiki/wiki/Backlight with the video group info? Or is that doc dead now?

@SrTobi
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SrTobi commented Nov 3, 2020

I have this problem at the moment. Light is working with sudo, but does nothing without.
groups command shows users wheel disk audio video networkmanager for my user.

Has something changed? or is there something I can do to investigate further?

@xaverdh
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xaverdh commented Nov 4, 2020

did you set programs.light.enable = true;?

@SrTobi
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SrTobi commented Nov 6, 2020

Hi, yes it was set... but also began to work now. I don't know why or what changed... maybe a restart? but I thought I already had tried to reboot.

@edrex
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edrex commented Mar 3, 2023 •
edited

Okso

  • light doesn't report permission errors by default. Use light -v 3 to see errors.
  • adding light package to user env doesn't install the needed udev rule, so requires sudo light .... This is as expected.
  • To install the udev rule file, NixOS programs.light.enable is needed.
  • To get the permissions from the rule file applied without restarting, run sudo systemctl restart systemd-udev-trigger.service. (udevadm control --reload-rules && udevadm trigger isn't sufficient, not sure why but see systemctl cat systemd-udev-trigger.service). This seems like a bug. Shouldn't installing new rule files trigger this unit to restart? I searched through past issues but didn't find a clear answer.

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@edrex @asheshambasta @dtzWill @SrTobi @xaverdh @rjpcasalino @emmanuelrosa @rokk4