Install ssh-askpass-gnome by entering the following commands in the terminal:
sudo apt update sudo apt install ssh-askpass-gnome
Description:
interactive X program to prompt users for a passphrase for ssh-add
This has been split out of the main openssh-client package so that openssh-client does not need to depend on GTK+. . You probably want the ssh-askpass package instead, but this is provided to add to your choice and/or confusion.
Homepage: http://www.openssh.com/
Version: 1:7.6p1-4
Section: universe/gnome