grass644 software package provides virtual package provided by grass-core, you can install in your Debian 8 (Jessie) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install grass644
grass644 is installed in your system.
Make ensure the grass644 package were installed using the commands given below,
$ sudo dpkg-query -l | grep grass644*
You will get with grass644 package name, version, architecture and description in a table
| Distro | Debian 8 jessie |
| Section | Virtual packages |
| Package | grass644 |
| Version | |
| Description | virtual package provided by grass-core |
| Sub Section | virtual |