If you are new to Linux servers, you may be a little confused about the terminology used for new software. Sometimes you will hear the word “update”, and other times you will hear the word “upgrade”. The two should not be used interchangeably, as they can have very different and sometimes serious consequences.
First, it is important to understand how a Linux distribution works. The actually operating system, sometimes called GNU/Linux, consists of the Linux kernel and some components that work with it. Nevertheless, when you install a Linux server, you will actually get a lot of extra software that the distribution vendor has decided is important. You also get access to a software repository containing binary packages that the distribution vendor maintains.
Updates refer to minor fixes to the core operating system, software, or extra packages. These are usually security updates or bug fixes. The version of the Linux distribution will normally not increase. An update can be as simple as a single file or involve multiple software packages. For a server, you may have a long-term release of a Linux distribution that will be supported for 5 or even 10 years. Updates are crucial for the security of your system, but upgrades may not be necessary.
An upgrade is a complete system-wide snapshot version increase of all software within your Linux distribution. Your dedicated server will receive a new major kernel version, new libraries, new software packages, and may even have some new configuration file changes. In some cases, packages from the old version may not be compatible with the new one, and vice versa.
Because of this, you should be very careful when upgrading a server. Unless it is absolutely necessary, you should avoid it. When you perform your next hardware upgrade, that is the perfect time for a new version of Linux. Otherwise, just maintain the current version with updates.