Removing unused packages in Linux

To remove unused packages in Linux, we will use the following software:

• deborphan
• gtkorphan (GUI based)
• rpmorphan

References

• https://www.ostechnix.com/how-to-find-and-remove-unused-packages-in-linux/

Deleting files specified in a text based file list

To delete a list of files specified in a text based file list, do the following:

> for /f %i in (files_to_delete.txt) do del %i

Reference:
https://superuser.com/questions/355584/how-to-delete-files-from-a-folder-using-a-list-of-file-names-in-windows

Export text based file list for the difference between 2 directories (Windows version)

The following is a tutorial for exporting a text-based file list showing the difference between 2 directories (e.g. D:\DirA, D:\DirB):

Step 1: Create a text-based file list for both directories

> cd D:\DirA
> dir /s /b /a:-d > file-list-dir-a.txt
> cd D:\DirB
> dir /s /b /a:-d > file-list-dir-b.txt

Step 2: Use WinMerge to get the difference between the 2 file lists:

Note: To display difference only, you need to set "View > Diff Context > 0 Lines".

Step 3: Copy the difference from WinMerge and create a text file to store it.

Ubuntu dock shows applications in current workspace only

In Ubuntu dock, to show applications in current workspace only, run the following command:

$ gsettings set org.gnome.shell.extensions.dash-to-dock isolate-workspaces true

References

• https://askubuntu.com/questions/992558/how-can-i-configure-the-ubuntu-dock-to-show-windows-only-from-the-current-worksp
• https://extensions.gnome.org/extension/887/workspace-isolated-dash/

Running Springboot web app in IntelliJ Idea Community Edition

When you run your springboot application in IntelliJ idea Community Edition having the following error, you can try the solution below to solve the problem.

Error "Failed to introspect annotated methods on class org.springframework.boot.web.servlet.support.SpringBootServletInitializer"

If your "pom.xml" has dependency with "provided" scope, you may have trouble when running your application in IntelliJ Idea Community Edition.

<dependency>   

  <groupId>org.springframework.boot</groupId>   

  <artifactId>spring-boot-starter-tomcat</artifactId>   

  <scope>provided</scope>

</dependency>

Some suggests that you can change the scope from "provided" to "compile". Here is another solution for this issue:

In your "Run/Debug Configurations", check "Include dependencies with 'Provided' scope". Then you can run the application from IntelliJ Idea Community Edition.

Image bytes to np array in Python

For reference:

# data - image bytes

im = Image.open(BytesIO(data))
I =  numpy.asarray(im)
print("I type:", type(I), "I shape:", I.shape)

>> I type: <class 'numpy.ndarray'> I shape: (512, 512, 3)

Slow Ubuntu startup time due to apt-daily.service

The  apt-daily.service  makes users feel very slow when running at startup. There is a workaround to delay its execution after system boot up:

Do the following:
 sudo systemctl edit apt-daily.timer 

And paste the config to the config file:
 # apt-daily timer configuration override 
 [Timer] 
 OnBootSec=15min 
 OnUnitActiveSec=1d 
 AccuracySec=1h 
 RandomizedDelaySec=30min 

References:
https://askubuntu.com/questions/800479/ubuntu-16-04-slow-boot-apt-daily-service
https://ubuntu-mate.community/t/shorten-boot-time-apt-daily-service/12297

Android Emulator 29.2.0 problem with Ubuntu 19.04

It just crashed with segmentation fault.

Display card tested: Radeon RX 550, Intel UHD Graphics 630

From https://androidstudio.googleblog.com/2019/09/emulator-2920-stable.html, the OS may crashes with incompatible Vulkan drivers. 

Temporary rollback to emulator 29.1.12-5839083 as a workaround.

Adjust VirtualBox VMS BIOS time

Syntax

   VBoxManage modifyvm "VMS Name" --biossystemtimeoffset -ms

   Note:
   ms - milliseconds


For example

   VBoxManage modifyvm "VMS Name" --biossystemtimeoffset -86400000

Kalman filter

Just finding some resources for learning about Kalman filter, seems it is a very useful technique which applicable on a lot of different areas.

References:

https://blog.maddevs.io/reduce-gps-data-error-on-android-with-kalman-filter-and-accelerometer-43594faed19c