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

Conflict between pandas 0.25.0 and pandas-datareader 0.7.0

For Python users, there is a conflict between "pandas 0.25.0" and "pandas-datareader 0.7.0".

If you do an "from pandas_datareader import data", you will got a conflict:

    "ImportError: cannot import name StringIO from pandas.compat"

To get rid of this issue, use "pandas 0.24.2" + "pandas-datareader 0.7.0" instead.

Linux mounted NTFS partition as read-only suddenly

Sometimes in dual boot system (Windows / Linux), the NTFS partitions might have some problem causing the Linux mounted the NTFS partitions as read-only. To solve this problem, one might try following to see if it works:

Step 1: Unmount the partition first

This can be done via Disks application OR command line:

• e.g. umount -v /dev/sda1

Step 2: Run ntfsfix on the target partition

• e.g. sudo ntfsfix /dev/sda1

If the command is successful, the following output should be shown:

  Mounting volume... The disk contains an unclean file system (0, 0).

  Metadata kept in Windows cache, refused to mount.

  FAILED

  Attempting to correct errors... 

  Processing $MFT and $MFTMirr...

  Reading $MFT... OK

  Reading $MFTMirr... OK

  Comparing $MFTMirr to $MFT... OK

  Processing of $MFT and $MFTMirr completed successfully.

  Setting required flags on partition... OK

  Going to empty the journal ($LogFile)... OK

  Checking the alternate boot sector... OK

  NTFS volume version is 3.1.

  NTFS partition /dev/sda1 was processed successfully.

Step 3: Remount the partition

    The partition should be read-write enabled

NFC notes on NDEF message for URL

Just a note for encoding URL in NDEF message, the NDEF record should user TNF_WELL_KNOWN as its TNF. And NDEF record type should be RTD_URI. And the first byte could be encoded for different protocols (e.g. 0x01 = "http://www", 0x02 = "https://www", etc.

References:
Beginning NFC
Professional NFC Application Development for Android