Batch image reduction in Linux

The ImageMagick toolkit is used.
@ Ubuntu
Sudo apt-Get install ImageMagick

Reference
$ Convert-resize 50% x50 % 1.jpg unzip small.jpg
You can reduce the size of 1.jpg to 1/4.
Reference
$ Convert-sample 400x300 1.jpg unzip small.jpg
The size of 1.jpg can be reduced to 400x300.
Note that the two ratios/numbers are separated by the letter X, not the multiplication number.

Then let's make a batch conversion (the online tutorial is for, although I prefer find)
Reference
For IMG in 'ls *. jpg '; do convert-resize 50% x50 % $ IMG small _ $ IMG; done

If you want to recursively convert the image of the current directory and subdirectory, use find:
Reference
Find-name "*. jpg"-exec convert-resize 50% x50 % {} found 2.16.small.jpg