DEV Community: Nur Kholis M

Change Brightness in Linux Desktop

Nur Kholis M — Thu, 27 Aug 2026 08:21:14 +0000

Issue

I don't know why PC doesn't have brightness screen control in linux desktop. Only laptop have it.

Some recommend to use ddcutil:

$ sudo ddcutil detect
Display 1
   I2C bus:  /dev/i2c-6
   DRM connector:           card1-DP-3
   EDID synopsis:
      Mfg id:               SKY - SKYDATA S.P.A.
      Model:                H24G30Q
      Product code:         9233  (0x2411)
      Serial number:        0000000000000
      Binary serial number: 0 (0x00000000)
      Manufacture year:     2024,  Week: 34
   VCP version:         2.1
$ sudo ddcutil getvcp 10
VCP code 0x10 (Brightness            ): current value = 0, max value = 100

My monitor already have 0 brightness but it still look too bright for me. Until i found xrandr, it can make my screen brightness to black completely.

$ xrandr --output DP-3 --brigtness 0.0

Then I make bash-script change-brightness.sh to make it simpler. but everytime I want to change brightness I have to go to terminal, I want to just click the systray icon and slide the brightness just like regular people.

Fix

Then I found yad which can turn bash script into UI using GTK. I then change my script:

$ cat ~/.local/bin/change-brightness.sh
#!/bin/sh
MON=$(xrandr -q | grep " connected" | cut -f1 -d ' ')
XR=$(xrandr --verbose | grep -i brightness | cut -f2 -d ' ' | head -n1)
BrCur=`awk "BEGIN {print $XR*100}"`
BrMax="100"
BrMin="5"
Step="5"

yad --text "Output: $MON" --text-align=left \
    --scale --step $Step --mouse --skip-taskbar --min-value $BrMin --max-value $BrMax \
    --value $BrCur --print-partial --undecorated --width 300 \
    --on-top --escape-ok --no-buttons  --close-on-unfocus \
| while read BrNew; do
    xrandr --output $MON --brightness $(awk "BEGIN {print $BrNew/100}")
done

Add to xfce-panel

Open xfce4-panel Preferences > Items > Add "Launcher"

Click and Edit "Laucher"

Click "Add a new empty item"

Add your script here. make sure to use full path:

Now I can change my screen brightness from systray icon. 🎉

GlobalProtect: Unstable VPN make WiFi randomly disconnected

Nur Kholis M — Wed, 26 Aug 2026 04:54:25 +0000

Issue

I use GlobalProtect in my Xubuntu PC. I experience randomly Wifi disconnection while VPN is not stable. It is very annoying. VPN disconnection should not make wifi disconnected too.

Jul 24 14:00:38 dell NetworkManager[824]: <info>  [1784876438.3238] device (wlan0): new IWD device state is disconnected
Jul 24 14:00:38 dell NetworkManager[824]: <info>  [1784876438.3239] device (wlan0): state change: activated -> failed (reason 'supplicant-disconnect', sys-iface-state: 'managed')
Jul 24 14:00:38 dell NetworkManager[824]: <info>  [1784876438.3242] manager: NetworkManager state is now CONNECTING
Jul 24 14:00:38 dell NetworkManager[824]: <warn>  [1784876438.3247] device (wlan0): Activation: failed for connection 'wifi-01'
Jul 24 14:00:38 dell NetworkManager[824]: <info>  [1784876438.3257] device (wlan0): state change: failed -> disconnected (reason 'none', sys-iface-state: 'managed')
Jul 24 14:00:38 dell NetworkManager[824]: <info>  [1784876438.3258] dhcp4 (wlan0): canceled DHCP transaction
Jul 24 14:00:38 dell NetworkManager[824]: <info>  [1784876438.3258] dhcp4 (wlan0): activation: beginning transaction (timeout in 45 seconds)
Jul 24 14:00:38 dell NetworkManager[824]: <info>  [1784876438.3258] dhcp4 (wlan0): state changed no lease
Jul 24 14:00:38 dell dbus-daemon[746]: [system] Activating via systemd: service name='org.freedesktop.nm_dispatcher' unit='dbus-org.freedesktop.nm-dispatcher.service' requested by ':1.14' (uid=0 pid=824 comm="/usr/sbin/NetworkManager --no-daemon" label="unconfined")
Jul 24 14:00:38 dell systemd[1]: Starting NetworkManager-dispatcher.service - Network Manager Script Dispatcher Service...
Jul 24 14:00:38 dell systemd[1]: Started NetworkManager-dispatcher.service - Network Manager Script Dispatcher Service.
Jul 24 14:00:38 dell NetworkManager[824]: <info>  [1784876438.6953] device (wlan0): new IWD device state is connecting
Jul 24 14:00:38 dell NetworkManager[824]: <info>  [1784876438.6976] device (wlan0): Activation: starting connection 'wifi-01' (3538330f-b11d-462b-93c0-edf1723f74a7)
Jul 24 14:00:38 dell NetworkManager[824]: <info>  [1784876438.6979] device (wlan0): state change: disconnected -> prepare (reason 'none', sys-iface-state: 'managed')
Jul 24 14:00:38 dell NetworkManager[824]: <info>  [1784876438.6992] device (wlan0): state change: prepare -> config (reason 'none', sys-iface-state: 'managed')
Jul 24 14:00:39 dell NetworkManager[824]: <info>  [1784876439.6444] device (wlan0): new IWD device state is connecting
Jul 24 14:00:39 dell NetworkManager[824]: <warn>  [1784876439.6444] device (wlan0): IWD is connecting to the wrong AP, replacing activation
Jul 24 14:00:39 dell NetworkManager[824]: <info>  [1784876439.6448] device (wlan0): state change: config -> disconnected (reason 'supplicant-disconnect', sys-iface-state: 'managed')
Jul 24 14:00:39 dell NetworkManager[824]: <info>  [1784876439.6494] device (wlan0): Activation: starting connection 'wifi-01' (5eca904e-d162-4b2f-8f8d-7b43a93ded07)
Jul 24 14:00:39 dell NetworkManager[824]: <info>  [1784876439.6498] device (wlan0): state change: disconnected -> prepare (reason 'none', sys-iface-state: 'managed')
Jul 24 14:00:39 dell NetworkManager[824]: <info>  [1784876439.6512] device (wlan0): state change: prepare -> config (reason 'none', sys-iface-state: 'managed')
Jul 24 14:00:39 dell NetworkManager[824]: <info>  [1784876439.7139] device (wlan0): new IWD device state is connected
Jul 24 14:00:39 dell NetworkManager[824]: <info>  [1784876439.7143] device (wlan0): state change: config -> ip-config (reason 'none', sys-iface-state: 'managed')
Jul 24 14:00:39 dell NetworkManager[824]: <info>  [1784876439.7152] dhcp4 (wlan0): activation: beginning transaction (timeout in 45 seconds)
Jul 24 14:00:41 dell NetworkManager[824]: <info>  [1784876441.7397] dhcp4 (wlan0): state changed new lease, address=192.168.1.12, acd pending
Jul 24 14:00:41 dell NetworkManager[824]: <info>  [1784876441.8913] dhcp4 (wlan0): state changed new lease, address=192.168.1.12
Jul 24 14:00:41 dell NetworkManager[824]: <info>  [1784876441.8923] policy: set 'wifi-01' (wlan0) as default for IPv4 routing and DNS
Jul 24 14:00:41 dell NetworkManager[824]: <info>  [1784876441.9060] device (wlan0): state change: ip-config -> ip-check (reason 'none', sys-iface-state: 'managed')
Jul 24 14:00:41 dell NetworkManager[824]: <info>  [1784876441.9079] device (wlan0): state change: ip-check -> secondaries (reason 'none', sys-iface-state: 'managed')
Jul 24 14:00:41 dell NetworkManager[824]: <info>  [1784876441.9081] device (wlan0): state change: secondaries -> activated (reason 'none', sys-iface-state: 'managed')
Jul 24 14:00:41 dell NetworkManager[824]: <info>  [1784876441.9086] manager: NetworkManager state is now CONNECTED_SITE
Jul 24 14:00:41 dell NetworkManager[824]: <info>  [1784876441.9090] device (wlan0): Activation: successful, device activated.
Jul 24 14:00:42 dell NetworkManager[824]: <info>  [1784876442.4536] manager: NetworkManager state is now CONNECTED_GLOBAL

Cause

Later I know that GlobalProtect is managed by NetworkManager by default. So when GP get unstable all other interface managed by NM will also affected.

Fix

Make NetworkManager not managed GlobalProtect.

$ vim /etc/NetworkManager/conf.d/99-globalprotect.conf
[keyfile]
unmanaged-devices=interface-name:gpd0

Change gpd0 interface match to your environment.

Restart NM:
$ sudo systemctl restart NetworkManager

LightDM: Disable Numlock active

Nur Kholis M — Wed, 26 Aug 2026 04:32:57 +0000

Issue

My Numlock indicator always turn on when LightDM login display. Since I'm using mini/laptop size keyboard which doesn't have any specific number key, it make annoying when inputting user password. My keyboard char U, I, O, J, K, L, M become number 4, 5, 6, 1, 2, 3, 0

Cause

LightDM in xubuntu have several default startup script in path /usr/share/lightdm/lightdm.conf.d/:

/usr/share/lightdm/lightdm.conf.d/
├── 50-disable-guest.conf
├── 50-disable-log-backup.conf
├── 50-greeter-wrapper.conf
├── 50-guest-wrapper.conf
├── 50-ubuntu.conf
├── 50-unity-greeter.conf
├── 50-xserver-command.conf
├── 50-xubuntu-numlock.conf
├── 60-lightdm-gtk-greeter.conf
└── 60-xubuntu.conf

One of the is 50-xubuntu-numlock.conf:

$ cat lightdm.conf.d/50-xubuntu-numlock.conf
[Seat:*]
greeter-setup-script=xubuntu-numlockx

Fix

Just disable that script by renaming it:

$ sudo mv /usr/share/lightdm/lightdm.conf.d/50-xubuntu-numlock.conf{,.disabled}

Fix LightDM Flicker Screen

Nur Kholis M — Thu, 06 Aug 2026 04:07:07 +0000

Issue

My login screen got flicker and black/blank screen when I move the cursor or press any key.
I believe it because lightdm use wrong frequency of my monitor. Lets fix it:

Fix

1. Identify your current display information

$ xrandr -q
Screen 0: minimum 320 x 200, current 2560 x 1440, maximum 16384 x 16384
DisplayPort-0 connected primary 2560x1440+0+0 (normal left inverted right x axis y axis) 527mm x 296mm
   2560x1440    165.00 + 144.00 + 119.99    59.95*
   2560x1440i   240.00   199.89
   1920x1080    120.00   119.88    60.00    60.00    50.00    59.94
   1680x1050     59.95
   1280x1024     75.02    60.02
   1440x900      59.89
   1280x720      60.00    50.00    59.94
   1024x768      75.03    70.07    60.00
   800x600       72.19    75.00    60.32    56.25
   720x576       50.00
   720x480       60.00    59.94
   640x480       75.00    72.81    60.00    59.94
   720x400       70.08
   2560x1440_60.00  59.96

It will display all existing available options in your current hardware. I choose first line.

2. Create script to force to use 60Hz frequency

$ vim /etc/lightdm/lightdm-xrandr.sh
#!/usr/bin/bash
xrandr --output DisplayPort-0 --mode 2560x1440 --rate 59.95

$ chmod +x /etc/lightdm/lightdm-xrandr.sh

3. Add script to lightdm

$ sudo cat lightdm.conf.d/80-flicker-fix.conf
[Seat:*]
display-setup-script=/etc/lightdm/lightdm-xrandr.sh

Refs

https://share.google/aimode/UrKzqwhzmI3QnENhP

Fix Radeon HD 6400 Series (Caicos) on Ubuntu

Nur Kholis M — Thu, 29 May 2025 02:06:22 +0000

Hi, I got my old VGA card black/blank display when using Ubuntu 24.04. On Windows 10 it is work perfectly on 1440p (2K) resolution.

Here is my VGA card info:

$ lspci -k -d ::03xx                                                                                                                                      
01:00.0 VGA compatible controller: Advanced Micro Devices, Inc. [AMD/ATI] Caicos [Radeon HD 6450/7450/8450 / R5 230 OEM]                                  │
        Subsystem: Bitland(ShenZhen) Information Technology Co., Ltd. Radeon HD 6450                                                                      
        Kernel driver in use: radeon                                                                                                                      
        Kernel modules: radeon, amdgpu

This old card correctly use radeon driver instead of newer amdgpu driver. I also can confirm driver is works well by executing DRI_PRIME=1 glxgears while monitoring Radeon GPU usage with radeontop utility.

But still monitor will be blank if change from onboard Intel GPU (i915) to Radeon GPU on PCIe interface. 😭

After days of googling, go to forums, try and error. ChatGPT is life saver 😃

Here options need to grub config /etc/default/grub to fix those issue:

#GRUB_CMDLINE_LINUX_DEFAULT="quiet splash"
GRUB_CMDLINE_LINUX_DEFAULT="radeon.si_support=1 radeon.cik_support=1 amdgpu.si_support=0 amdgpu.cik_support=0 radeon.dpm=0 radeon.audio=0 radeon.modeset=1"

Then sudo update-grub

It now my monitor can display 2560x1440p (2K) again. yay...🎉

Selenium: chromedriver dismatch version

Nur Kholis M — Fri, 15 Mar 2024 09:11:22 +0000

Issue

Selenium failed to run with these error messages;

selenium.common.exceptions.SessionNotCreatedException: Message: session not created: This version of ChromeDriver only supports Chrome version 114
Current browser version is 122.0.6261.129 with binary path /Applications/Google Chrome.app/Contents/MacOS/Google Chrome
Stacktrace:
0   chromedriver                        0x000000010f9746b8 chromedriver + 4937400
1   chromedriver                        0x000000010f96bb73 chromedriver + 4901747
2   chromedriver                        0x000000010f529616 chromedriver + 435734
3   chromedriver                        0x000000010f55bd10 chromedriver + 642320
4   chromedriver                        0x000000010f55718a chromedriver + 622986
5   chromedriver                        0x000000010f55367c chromedriver + 607868
6   chromedriver                        0x000000010f59aa08 chromedriver + 899592
7   chromedriver                        0x000000010f599ebf chromedriver + 896703
8   chromedriver                        0x000000010f590de3 chromedriver + 859619
9   chromedriver                        0x000000010f55ed7f chromedriver + 654719
10  chromedriver                        0x000000010f5600de chromedriver + 659678
11  chromedriver                        0x000000010f9302ad chromedriver + 4657837
12  chromedriver                        0x000000010f935130 chromedriver + 4677936
13  chromedriver                        0x000000010f93bdef chromedriver + 4705775
14  chromedriver                        0x000000010f93605a chromedriver + 4681818
15  chromedriver                        0x000000010f90892c chromedriver + 4495660
16  chromedriver                        0x000000010f953838 chromedriver + 4802616
17  chromedriver                        0x000000010f9539b7 chromedriver + 4802999
18  chromedriver                        0x000000010f96499f chromedriver + 4872607
19  libsystem_pthread.dylib             0x00007fff2058b8fc _pthread_start + 224
20  libsystem_pthread.dylib             0x00007fff20587443 thread_start + 15

Caused

Missmatch version between chrome and chromedriver

Fix

Download matched version of chromedriver here. then copy to /opt/local/bin/chromedriver in macOS with macports.

Refs

Unable to join domain

Nur Kholis M — Wed, 06 Mar 2024 10:03:26 +0000

Issue

Unable to join domain to Active Directory server with these error

GSSAPI Error: Unspecified GSS failure. Minor code may provide more information (Server not found in Kerberos database) ...
! Couldn't authenticate to active directory: SASL(-1): generic failure: GSSAPI Error: Unspecified GSS failure. Minor code may provide more information (Server not found in Kerberos database) 
adcli: couldn't connect to [redacted] domain: Couldn't authenticate to active directory: SASL(-1): generic failure:  
! Insufficient permissions to join the domain realm: Couldn't join realm: Insufficient permissions to join the domain ...

Caused

Some UDP port is blocked by firewall

53/udp  open
123/udp open|filtered
88/udp  open|filtered
389/udp open|filtered
464/udp open|filtered
137/udp open|filtered
138/udp open|filtered
636/udp open|filtered

Resolution

Open firewall to these UDP port on AD server

53/udp  open
123/udp open
88/udp  open|filtered
389/udp open
464/udp open|filtered
137/udp open|filtered
138/udp open|filtered
636/udp closed

References

How to find valid Knox Service Name in Ranger Policy

Nur Kholis M — Wed, 06 Mar 2024 04:20:44 +0000

Issue

We don't have any clue what is name of valid service for "Knox Service" entry in Ranger Policies UI

Resolution

You can find all knox service name in /var/lib/knox/gateway/conf/topologies/cdp-proxy.xml

Here is the full list:

ATLAS
ATLAS-API
CM-API
CM-UI
CRUISE-CONTROL
HBASEUI
HDFSUI
HUE
IMPALA
IMPALAUI
JOBHISTORYUI
KUDUUI
LIVYSERVER
LIVY_FOR_SPARK3
NAMENODE
OOZIE
OOZIEUI
RANGER
RANGERUI
RESOURCEMANAGER
RESOURCEMANAGERAPI
SCHEMA-REGISTRY
SMM-API
SMM-UI
SOLR
SPARK3HISTORYUI
SPARKHISTORYUI
WEBHDFS
YARNUI
YARNUIV2
ZEPPELINUI
ZEPPELINWS