If you are a user of Debian 8 Jessie and wish to continue receiving security updates, you must update to the latest version, Debian 9 Stretch as soon as possible. The previous release of this Linux distro, which was released in 2015 has stopped to have support and, therefore, will no longer receive regular security updates.
From now on, the integrity of the system is not guaranteed in case of stability, performance or safety failures. The Debian LTS team will continue to maintain Debian 8 until June 2020, but will only release patches for the vulnerabilities they consider most critical.
To update to the most recent version, Debian 9.4, it is first recommended to perform a system check to eliminate obsolete packages that may create problems during the update process. Simply start your terminal and execute the command aptitude search '~ o'.
The next step will be to proceed with the update. To update the repositories, applications and packages of the distribution we will execute apt-get update, apt-get upgrade and apt-get dist-upgrade.
Once this is done it is advisable to execute a series of commands to verify that you have all the packages installed and thus move the software repositories from Jessie to Stretch: dpkg -C, sed -i ' s / jessie / stretch / g '/etc/apt/sources.list and apt-get update.
After following these steps you just need to restart the system to start using Debian 9 Stretch, which will have basic support until 2020 and extended support until 2022.