sudo apt-get upgrade: 不會對系統產生重大的影響，可以在任何時候運行。

sudo apt-get dist-upgrade: 涉及核心的升級，通常會對系統功能產生實際的影響，可能在需要的情況下卸載一些已經安裝的軟件也可能安裝一些額外的軟件，通常應該謹慎操作，特別是有未完成的工作，但是在允許的情況下應該盡力升級，應為可能涉及一些重大的核心升級，比如安全。

dist-upgrade will perform updates to software that makes actual changes to the system and can have an impact on the functionality of your system. Using ubuntu, a dist-upgrade often involves kernel upgrades. Kernel upgrades can really change things, especially if you have manually installed proprietary drivers. If you are currently working on a project for school or work, it is best to wait until the project is finished before performing a dist-upgrade. You can safely perform an upgrade at any time and it will not have a large impact on system functionality. You should, however, perform a dist-upgrade whenever possible as there are often security updates for the kernel. Also, a dist-upgrade may uninstall existing packages or install extra packages where an upgrade will not.

upgrade
   upgrade is used to install the newest versions of all packages
   currently installed on the system from the sources enumerated in
   /etc/apt/sources.list. Packages currently installed with new
   versions available are retrieved and upgraded; under no
   circumstances are currently installed packages removed, or packages
   not already installed retrieved and installed. New versions of
   currently installed packages that cannot be upgraded without
   changing the install status of another package will be left at
   their current version. An update must be performed first so that
   apt-get knows that new versions of packages are available.

dist-upgrade
   dist-upgrade in addition to performing the function of upgrade,
   also intelligently handles changing dependencies with new versions
   of packages; apt-get has a "smart" conflict resolution system, and
   it will attempt to upgrade the most important packages at the
   expense of less important ones if necessary. So, dist-upgrade
   command may remove some packages. The /etc/apt/sources.list file
   contains a list of locations from which to retrieve desired package
   files. See also apt_preferences(5) for a mechanism for overriding
   the general settings for individual packages.
 

ref: https://www.quora.com/What-does-command-sudo-apt-get-dist-upgrade

ref: https://askubuntu.com/questions/81585/what-is-dist-upgrade-and-why-does-it-upgrade-more-than-upgrade

ubuntu sudo apt-get upgrade 和 sudo apt-get dist-upgrade區別