$ sudo apt-get update
$ sudo apt-get install monodevelop-debugger-gdb 

monodevelop-debugger-gdb is installed in your system.

Make ensure the monodevelop-debugger-gdb package were installed using the commands given below,

$ sudo dpkg-query -l | grep monodevelop-debugger-gdb *

You will get with monodevelop-debugger-gdb package name, version, architecture and description in a table

monodevelop-debugger-gdb package basic information: