gdb64 software package provides GNU Debugger (64-bit), you can install in your Ubuntu 16.04 LTS (Xenial Xerus) by running the commands given below on the terminal,
$ sudo apt-get update $ sudo apt-get install gdb64
gdb64 is installed in your system.
Make ensure the gdb64 package were installed using the commands given below,
$ sudo dpkg-query -l | grep gdb64 *
You will get with gdb64 package name, version, architecture and description in a table
| Distro | Ubuntu 16 04 lts xenial xerus |
| Section | Development |
| Package | gdb64 |
| Version | 7.11-0ubuntu1 |
| Description | GNU Debugger (64-bit) |
| Sub Section | Devel |