Installing Remmina on Debian Stretch

1. Add the repository to apt. Create the file /etc/apt/sources.list.d/remmina.list with the following content:
   
   

   deb http://ftp.debian.org/debian stretch-backports main

   
   
2. Update packages:
   
   

   sudo apt-get update

   
   
3. Install Remmina:
   
   

   sudo apt install -t stretch-backports remmina remmina-plugin-rdp remmina-plugin-secret

   
   

Source: https://remmina.org/how-to-install-remmina/