Use krename application.

jhead -n%Y%m%d-%H%M%S *.jpg 

exiv2 -k -r '%Y-%m-%d_%H-%M-%S_:basename:' rename “$i” exiv2 -v -r '%Y%m%d.%H%M%S.:basename:' rename “$i”

exiftool -d %Y-%m-%d_%H-%M-%S%%-c.%%e "-filename<CreateDate" DIR 
If you want to keep track of original filename and write extension lower case:
 
exiftool -d %Y%m%d_%H%M%S%%-c-%%f.%%le "-filename<DateTimeOriginal" [.|DIR]
The same works also with the whole filename in lowercase:
 
exiftool -d %Y%m%d_%H%M%S%%-c-%%lf.%%le "-filename<DateTimeOriginal" [.|DIR]

for i in *.jpg; do echo "Processing $i"; exiftool -all= "$i"; done