using 'ChatGPT' instead of 'Googling'

 Nowadays, many queries can be more accurately answered by Copilot or ChatGPT or Gemini rather than just doing a web search - for eg, we could just copy-paste error messages which we got on trying to run an AWS VM image with virtualbox, and chatgpt gave accurate fixes. Gemini / Copilot providing links to references is another very useful feature, using which we can double-check if the references match our environment etc.

no python found

When getting the error "no python found" even after 
sudo apt-get install python
"python is already the newest version." 

https://stackoverflow.com/questions/3655306/ubuntu-usr-bin-env-python-no-such-file-or-directory

If Python 3 is not installed, install it: sudo apt-get install python3

Then, a good option is to install sudo apt install python-is-python3

Or, invoke python3 instead of just python. Or, create a symlink 

whereis python3
sudo ln -s /usr/bin/python3 /usr/bin/python

simple http server for debugging, in one line of python

 https://linuxconfig.org/running-a-simple-http-web-server-with-one-terminal-command-and-python

We just need to run the following line in the directory which we want as the server's home directory - 

python3 -m http.server --bind 127.0.0.1 9000

Used this while troubleshooting OpenSpace showcomposer ui issues.

git error remote origin already exists

 Via https://dev.to/devmercy/four-ways-to-solve-the-remote-origin-already-exists-error-1f2

git remote remove origin

git remote set-url origin https://github.com/newgit/url.git

Or, we can, instead of removing the URL called origin, rename it,

git remote rename origin backup

Or we might have already set the origin correctly, which we can then check using

git remote -v

which will list all remotes.

a lot of github workflows

Learnt a lot about many different workflows, how to get various things done, which can be used in future for incorporating into various projects.

• automated deb creation with auto dependency detection
• build opencv with cuda support
• ffmpeg linking on Windows
• Make CMake display a message on the console
• android apps without android studio

automated deb creation with auto dependency detection

Apparently, CMake can do some automation for us - with CMake,

set (CPACK_DEBIAN_PACKAGE_SHLIBDEPS ON)

https://www.guyrutenberg.com/2012/07/19/auto-detect-dependencies-when-building-debs-using-cmake/

https://cmake.org/cmake/help/latest/cpack_gen/deb.html#variable:CPACK_DEBIAN_PACKAGE_SHLIBDEPS

for more info

Example of multi-package build on github actions - 

https://github.com/giuspen/cherrytree/blob/master/build.sh

build opencv with cuda support

https://github.com/luxonis/depthai-core/issues/885

Package 'libtbb2' has no installation candidate

Trying

libtbbmalloc2

https://gist.github.com/kanaryayi/115731930a9767d8607374552993bad3 - Install OpenCV 4.9 with CUDA support - this gist has some build flags which are useful, and also dependencies.

CUDA backend requires CUDA Toolkit - we need to download it from the NVIDIA website.
https://developer.nvidia.com/cuda-toolkit

wget https://developer.download.nvidia.com/compute/cuda/repos/ubuntu2404/x86_64/cuda-keyring_1.1-1_all.deb

sudo dpkg -i cuda-keyring_1.1-1_all.deb

sudo apt-get update

sudo apt-get -y install cudnn cuda-toolkit

get url from

https://developer.nvidia.com/cuda-downloads?target_os=Linux&target_arch=x86_64

(deb network install)

More options are at

https://docs.nvidia.com/cuda/cuda-installation-guide-linux/#meta-packages

CMake Warning at /home/sssvv/opencv_contrib/modules/cudacodec/CMakeLists.txt:26 (message):

  cudacodec::VideoReader requires Nvidia Video Codec SDK.  Please resolve

  dependency or disable WITH_NVCUVID=OFF

CMake Warning at /home/sssvv/opencv_contrib/modules/cudacodec/CMakeLists.txt:30 (message):

  cudacodec::VideoWriter requires Nvidia Video Codec SDK.  Please resolve

  dependency or disable WITH_NVCUVENC=OFF

But this page says,

https://developer.nvidia.com/nvidia-video-codec-sdk/download

"FFMPEG is a cross-platforms solution to record, convert, and stream audio and video. FFMPEG supports video hardware acceleration on NVIDIA GPUs."

So do we really need cuda support? (for using NVidia nvenc codec with opencv)

I've put in a question at the OpenCV forum, no answers so far.

https://forum.opencv.org/t/make-videowriter-use-h264-nvenc-codec/21049

Maybe I can try downloading the Nvidia Video Codec SDK, compile OpenCV with that, and then try again.

Learnt how to build with Windows / Linux, building the latest OpenCV and ffmpeg from source, 
Windows workflow - setting PKG_CONFIG_PATH is important here.

Linux workflow - uses actions/cache to cache OpenCV once it is built.

ffmpeg linking on Windows

https://stackoverflow.com/questions/77742801/how-do-i-include-ffmpeg-for-development-in-a-windows-program

(long answer)

choco install ffmpeg has the issue that the pc files are not present - mention of pc files here,

https://stackoverflow.com/questions/77747559/how-can-i-install-ffmpeg-so-that-pkg-config-can-find-it

Solution was to download from https://github.com/BtbN/FFmpeg-Builds/

https://github.com/hn-88/test-ffmpeg-codec-listing has Windows and Linux workflows.

https://people.freedesktop.org/~dbn/pkg-config-guide.html provided help on how to use pkg-config, and the full discussion is at https://github.com/hn-88/test-ffmpeg-codec-listing/issues/1

Make CMake display a message on the console

Equivalent of echo "our hello world" would be message("our hello world") - https://cmake.org/cmake/help/book/mastering-cmake/chapter/Writing%20CMakeLists%20Files.html

android apps without android studio

Directly building android apps on github actions - for learning, there is gradle init as mentioned at https://medium.com/@sdiony/can-you-really-develop-android-apps-without-android-studio-cdd9b951de65

but copy-pasting from existing projects, samples, is much easier - 
https://github.com/hn-88/OpenCV-android-samples
https://github.com/hn-88/android-ndk-samples/

Indian income tax filing - a good overview guide

 Valueresearch has a good guide on what to keep ready, at https://www.valueresearchonline.com/stories/224462/income-tax-return-filing-preparation/

1. Form16
2. Form 26AS
3. Capital gains statements
4. Interest certificates
5. Investment / donation proofs (for old tax regime)
6. Loan interest certificates - home loan, EV loan interest may have deductions
7. Bank account details
8. Wait till AIS / TIS / 26AS is ready to avoid re-filing

While I knew about the other points, I was not very clear about significance of 26AS, and how to access TIS etc. AIS = Annual Information Statement, TIS = Taxpayer Information Summary according to this FAQ page which has lots of information - https://www.incometax.gov.in/iec/foportal/ais-faq 

Edit: 17th May 2025 - the TIS / AIS for me has info from LIC, SBI and HDFC as well as the mutual fund companies, but not from Canara Bank (savings bank interest.) I guess Canbank's reporting system to the government is not fully functional.

I can check / reconcile the following from TIS - 

1. Interest - Savings Bank
2. Interest - Deposits
3. LIC receipts
4. MF sale
5. MF purchase

diskpart instead of fdisk on windows 11

As the title suggests, used diskpart to delete an EFI partition, since fdisk is no longer bundled with Windows 11. An earlier post has the syntax - https://hnsws.blogspot.com/2023/09/delete-efi-partition-with-windows.html

Then also created a partition and formatted it within diskpart, https://adminhowto.com/how-to-reformat-a-usb-drive-using-windows-diskpart/

create partition primary

format fs=fat32 quick

refreshed github token

 Refreshed a github personal access fine-grained token by logging on to the relevant account and going to https://github.com/settings/personal-access-tokens/

For uploading files to a repository, the permissions needed are:

User permissions: None

Per-repository permissions: (for the relevant repo) 

Read access to metadata
Read and write access to actions, code, and workflows.

The post about google apps script code to auto-upload to github-pages is at https://hnsws.blogspot.com/2024/03/workaround-for-cors-errors-on-api-calls.html 

qemu for arm64 on x86_64 Linux machine

This is just documenting the various points to note, trials, errors etc when I tried to run arm64 on x86_64 using qemu. This post does not have a very satisfactory ending - the VM was far too slow for me to try OpenSpace or OCVWarp or anything else for arm64 tests.

Via bing copilot

https://documentation.ubuntu.com/server/how-to/virtualisation/qemu/index.html#boot-arm64-virtual-machines-on-qemu

https://documentation.ubuntu.com/server/how-to/graphics/gpu-virtualization-with-qemu-kvm/#gpu-virtualization-with-qemu-kvm

general qemu setup 

https://christitus.com/vm-setup-in-linux/

from

https://www.youtube.com/watch?v=Kq849CpGd88

qemu-system-aarch64 \

 -m 2048\

 -cpu max \

 -M virt \

 -nographic \

 -drive if=pflash,format=raw,file=efi.img,readonly=on \

 -drive if=pflash,format=raw,file=varstore.img \

 -drive if=none,file=noble-server-cloudimg-arm64.img,id=hd0 \

 -device virtio-blk-device,drive=hd0 \

 -netdev type=tap,id=net0 \

 -device virtio-net-device,netdev=net0

could not find net0, so tried

without network

---------------

qemu-system-aarch64 \

 -m 2048\

 -cpu max \

 -M virt \

 -nographic \

 -drive if=pflash,format=raw,file=efi.img,readonly=on \

 -drive if=pflash,format=raw,file=varstore.img \

 -drive if=none,file=noble-server-cloudimg-arm64.img,id=hd0 \

 -device virtio-blk-device,drive=hd0 

This went into a loop around 10 minutes in,

[FAILED] Failed to start systemd-resolved.service - Network Name Resolution.

See 'systemctl status systemd-resolved.service' for details.

         Starting systemd-resolved.service - Network Name Resolution...

[FAILED] Failed to start systemd-resolved.service - Network Name Resolution.

See 'systemctl status systemd-resolved.service' for details.

         Starting systemd-resolved.service - Network Name Resolution...

[FAILED] Failed to start systemd-resolved.service - Network Name Resolution.

See 'systemctl status systemd-resolved.service' for details.

         Starting systemd-resolved.service - Network Name Resolution...

[    **] (1 of 2) Job apparmor.service/start running (13min 35s / no limit)

When running virt-manager,

"The emulator may not have search permissions for the path"

First run with sudo and then without?

https://askubuntu.com/questions/722034/permission-error-in-virtual-machine-manager

sudo virt-manager

(say yes when it asks to fix the problem, go to next step, then cancel)

then

virt-manager

That worked.

Chrome remote desktop is an option - 

https://medium.com/@selvamraju007/install-and-launch-ubuntu-22-04-desktop-on-google-cloud-1fba8c0f9585

https://remotedesktop.google.com/?pli=1

But not available for arm64?

Login incorrect

ubuntu login: password[  361.700501] cloud-init[1126]: Cloud-init v. 24.4.1-0ubuntu0~24.04.3 running 'modules:final' at Fri, 09 May 2025 07:42:17 +0000. Up 360.36 seconds.

Password: ci-info: no authorized SSH keys fingerprints found for user ubuntu.

Probably must run

virt-sysprep

https://stackoverflow.com/questions/29137679/login-credentials-of-ubuntu-cloud-server-image

--password ubuntu:password:ubuntu

sets the password ubuntu for the user ubuntu.

virt-sysprep [--options] -a disk.img

https://manpages.ubuntu.com/manpages/trusty/man1/virt-sysprep.1.html

virt-sysprep --password ubuntu:password:ubuntu -a ubuntu2404-arm64.img

sudo apt install libguestfs-tools

virt-customize --password ubuntu:password:ubuntu -a ubuntu2404-arm64.img

virt-customize -a ubuntu2404-arm64.img  --password ubuntu:password:ubuntu

Extra parameter on the command line: ‘ --password’.

Try ‘virt-customize --help’ or consult virt-customize(1) for more information

Needed to run as sudo.

sudo virt-customize -v -x -a ubuntu2404-arm64.img --root-password password:password

Boots up in around 5 minutes.

Increase size of disk

https://computingforgeeks.com/how-to-extend-increase-kvm-virtual-machine-disk-size/

sudo qemu-img resize /home/sssvv/Downloads/QEMU/noble-server-cloudimg-arm64.img +20G

qemu-img: Command not found: resize /home/sssvv/Downloads/QEMU/noble-server-cloudimg-arm64.img +20G

maybe needs converting to raw?

https://bobcares.com/blog/qemu-img-error-resizing-image-invalid-argument/

Jenkins and Github

 I was curious to know how Jenkins CI/CD works with Github, similar to what is seen on the OpenSpace repository. So one way is to use webhooks, as detailed in this guide,

Complete Step-by-Step Jenkins CICD with GitHub Integration | by Mudasir | Medium

bash: cannot execute: required file not found

bash: cannot execute: required file not found

The problem, it turned out, was an incorrect path in the shebang.

#!/bin/bash

echo "Hello, World!"

will fail on a machine which does not have bash at /bin (or a link to bash there). I believe cron jobs also have problems if the shebang does not directly point to bash? Anyway, we can always do a 

which bash

to find the correct path and enter it in the shebang.

download just one directory from github repository

 Via 
https://stackoverflow.com/questions/7106012/download-a-single-folder-or-directory-from-a-github-repository

https://downgit.github.io/

for using 

https://github.com/hn-88/android-ndk-samples/tree/main/hello-libs

in

https://github.com/hn-88/OpenCV-android-samples/

virtualizing Raspberry Pi on an iPad with UTM

 We can virtualize a Raspberry Pi with UTM, but need old 32 bit version, since 64 bit is broken on UTM, tho' QEMU works - 

https://github.com/utmapp/UTM/issues/4827

script to run multiple commands on a remote server over ssh

 Made Chatgpt write the following script. The EOF syntax is useful. In our case, we need to put in the appropriate -pPORT also.

write a bash shell script to ssh into two servers server1 and server2 with ssh keys key1.pem and key2.pem, run sudo apt upgrade on both, and show the result on the terminal.

#!/bin/bash

# Define servers and keys

SERVER1="user1@server1"

KEY1="key1.pem"

SERVER2="user2@server2"

KEY2="key2.pem"

# Function to upgrade a server

upgrade_server() {

  local SERVER=$1

  local KEY=$2

  echo "Upgrading packages on $SERVER..."

  

  ssh -i "$KEY" -o StrictHostKeyChecking=no "$SERVER" << 'EOF'

    echo "Running apt update..."

    sudo apt update

    echo "Running apt upgrade..."

    sudo DEBIAN_FRONTEND=noninteractive apt upgrade -y

EOF

}

# Upgrade both servers

upgrade_server "$SERVER1" "$KEY1"

echo "---------------------------------------------"

upgrade_server "$SERVER2" "$KEY2"

x86 Emulation on iPad with UTM

Continuing my earlier post about UTM - finally got JIT to work on iPad. Apparently I had been successful earlier also, but had thought that the QEMU error was due to JIT not being enabled. Going into settings (in the context menu of each VM, accessed by long-press) and trying to increase RAM, UTM gave the warning that the system had only 1700 MB of RAM left, of which 1300 or so was free, hence increasing the VM's RAM beyond this would cause crashes. Ubuntu 14.04 boots up in around 4 minutes. Unfortunately, maybe due to Ubuntu's behaviour when running on a display without acceleration, very slow to respond. Nearly a minute for keystrokes to appear on screen!

What I followed was this:

Installed AltStore via AltServer for Windows - https://faq.altstore.io/altstore-classic/how-to-install-altstore-windows

Installed StikJIT & StosVPN via AltStore - StikJIT user manual

https://github.com/StephenDev0/StikJIT/blob/main/user-manual.md

Copied over the pairing file created as per the user manual above, using iCloud Drive (Installed that also on the Windows machine.)

Then, the procedure is - 

• Swipe up from down and hold, to show all applications - swipe up applications which you want to close and start again with JIT, like UTM.
• Start StosVPN, click to start the connection
• Start StikJIT - one-time requirement of passing on the path to the pairing file, then
• Click Enable JIT - a few moments later, it prompts for which app to enable JIT for, from a list of apps - choose UTM, and then UTM opens up with JIT enabled. Can start up JMs at this point. 

But as mentioned in the first paragraph of this post, we need to choose those VM images (or create such VMs) which can work with 512 MB or 768 MB of RAM on this 9th gen iPad, since it has limited free RAM. Perhaps trying Raspberry Pi might be a good option.

monitoring websites for changes - followthatpage

 There was a request from one of my colleagues for suggestions - he wanted a tool to automatically let him know when some particular websites had changes. Something similar to an RSS feed for a website which doesn't have an RSS feed, I guess. 

I replied that I use

https://www.followthatpage.com/

to monitor up to 20 pages for free per account per day - so if you don't want daily checks, you can add more pages, too.

There are many other "freemium" and paid options, too. 

development for Android / iOS - preliminaries

Seeing that the mobile devices were quite competitive with the desktop's processing power in a previous post, thought about working on porting various tools like OCVWarp to Android and iOS if feasible.

OpenCV Android - had earlier cloned / forked NDK samples.

OpenCV for iOS - samples are at https://github.com/opencv/opencv_for_ios_book_samples

https://docs.opencv.org/4.11.0/d3/dc9/tutorial_table_of_content_ios.html

The binaries are available here 

https://sourceforge.net/projects/opencvlibrary/files/opencv-ios/

only up to OpenCV v3.4.3, but iOS framework seems to be available at

https://sourceforge.net/projects/opencvlibrary/

and

https://github.com/opencv/opencv/releases/tag/4.11.0

To check if swift playgrounds is available on 9th gen ipad - https://www.theverge.com/2021/6/15/22534902/ipad-pro-apple-swift-playgrounds-4-wwdc-2021

To check if example opencv apps can run on ipad.

info about various ARM platforms

 https://www.baeldung.com/linux/arm64-armel-armhf-overview

So, arm64 is sometimes referred to as aarch64. But the github arm64 appimage builds are not compatible with Ubuntu on raspberry pi 4 etc, maybe because of library differences, since the github runners are Ubuntu 24.04. 

simple logger created by chatgpt

I wanted to make a simple load-average logger. Thought of making ChatGPT do the typing, instead of me creating the simple code.

The result was quite OK.

https://github.com/hn-88/GSheetLoadLogger

The prompts and conversation are in the issues tab.

moving Virtualbox VMs to external drive

VirtualBox Manager
> Right-click on the VM
> Select "Move"
> Choose the new location and click "Move"

(Tho' the progress bar doesn't seem to work, it moved the VM and associated files to the external drive in approx the usual time it would take for a 12 GB file move.)