SSH returns: no matching host key type found. Their offer: ssh-dss

 Fix is

ssh -oHostKeyAlgorithms=+ssh-dss root@192.168.8.109

Read more here https://askubuntu.com/questions/836048/ssh-returns-no-matching-host-key-type-found-their-offer-ssh-dss 

format decimal and doubles in Java to desired decimal places

 To format numbers in java, simple

String.format("%.2f", 132.2372342)

Free up space in ubuntu server

 Clean old kernels

• Check for kernet is use : uname –r
• Check for old kernels : dpkg --get-selections | grep linux-image
• Remove unused kernels : dpkg --get-selections | grep linux-image

Clean APT (Pulled from https://askubuntu.com/questions/5980/how-do-i-free-up-disk-space)

• To delete downloaded packages (.deb) already installed (and no longer needed)
• sudo apt-get clean
• To remove all stored archives in your cache for packages that can not be downloaded anymore (thus packages that are no longer in the repository or that have a newer version in the repository).
• sudo apt-get autoclean
• To remove unnecessary packages (After uninstalling an app there could be packages you don't need anymore)
• sudo apt-get autoremove

Finally, Check Disk Space

• df -h /

view largest installed debian packages on unix

More details on this link https://www.commandlinefu.com/commands/view/3842/list-your-largest-installed-packages-on-debianubuntu

dpkg-query -Wf '${Installed-Size}\t${Package}\n' | sort -n | tail -n 10

See more details here https://linoxide.com/show-installed-package-size-ubuntu-debian/

pull multiple files from android via adb

Got answer from https://stackoverflow.com/questions/11074671/adb-pull-multiple-files

adb shell 'ls /sdcard/DCIM/Camera/20200327*.mp4' | tr -d '\r' | xargs -n1 adb pull

get the size of folder contents

du -sh 

Output

15M big_folder
0 dead.letter
4.0K some_file
4.0K some_other_file

challenges with grails unique: true

Grails does not evaluate a unique constraint at GORM level but at the database level

    static constraints = {
        property unique: true
    }

This means that you would not get a grails.validation.ValidationException but a org.springframework.dao.DataIntegrityViolationException.

This means that

domainInstance.validate()

would not capture a duplicate "property"