When logging into my Ubuntu server after not accessing it for a while some server information is shown when logging in via SSH.
As shown in the above image that message states I have 69 updates that can be applied immediately.
To resolve the issue run the update and upgrade commands.
sudo apt -y update && sudo apt -y upgrade
Due to the number of updates, the whole process can take a few minutes (For my updates it took around ten minutes).
During the upgrade process, some prompts might appear where you need to select some services to restart after the updates.
When logging into the server you may also see a message requesting the server to restart.
Use the reboot command to restart the server.
sudo reboot
You will be taken out of the session as the server will be restarted, wait a minute or so, and SSH back to ensure the server is up and running again.