It ain’t gonna do itself
As with major linux distributions, developers are constantly adding new code and features with the main goal of maintaining a system up to date in the face of constant software change.
In order to rest assured your linux system is up to date and smooth running, there are a few simple commands to execute from the terminal.
For CentOS/RHEL:
yum -y update
For Ubuntu/debian:
apt update && apt -y dist-upgrade
Keep in mind these updates generally come in effect after a system reboot. This is mainly due to new kernel version which cannot be loaded on-the-fly but rather at startup.
These update commands can be configured as a routine but since a reboot is required in most cases, it would be better to do manually at regular intervals.