ca-certificates software package provides Common CA certificates, 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 ca-certificates
ca-certificates is installed in your system.
Make ensure the ca-certificates package were installed using the commands given below,
$ sudo dpkg-query -l | grep ca-certificates *
You will get with ca-certificates package name, version, architecture and description in a table
| Distro | Ubuntu 16 04 lts xenial xerus |
| Section | Miscellaneous |
| Package | ca-certificates |
| Version | 20160104ubuntu1 |
| Description | Common CA certificates |
| Sub Section | Misc |