Ubuntu / Debian etc. using apt-get:
You should first run
upgrade. Neither of them
automatically runs the other.
apt-get update updates the list of available packages and their versions, but it does not install or upgrade any packages.
apt-get upgrade actually installs newer versions of the packages you have. After updating the lists, the package manager knows about
available updates for the software you have installed. This is why you
first want to
However with Red Hat / CentOS using yum the
update command will ask you if you want to apply the updates it finds.
$ sudo yum update
grabs a list of all available updates and asks you if you would like to apply them. Like this:
kf5-sonnet-core x86_64 5.33.0-1.el7 epel 150 k
kf5-sonnet-ui x86_64 5.33.0-1.el7 epel 141 k
Upgrade 52 Packages
Total size: 15 M
Is this ok [y/d/N]:
When your friend refers to update as "small changes" and upgrade as "big changes" he actually means the difference between upgrade and dist-upgrade.
From the apt-get manual:
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 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. The dist-upgrade
command may therefore 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