Смотрим вывод команды man aptitude:
safe-upgrade
Upgrades installed packages to their most recent version. Installed packages will not be removed unless they are unused (see the section
“Managing Automatically Installed Packages” in the aptitude reference manual). Packages which are not currently installed may be installed to
resolve dependencies unless the --no-new-installs command-line option is supplied.
If no <package>s are listed on the command line, aptitude will attempt to upgrade every package that can be upgraded. Otherwise, aptitude will
attempt to upgrade only the packages which it is instructed to upgrade. The <package>s can be extended with suffixes in the same manner as
arguments to aptitude install, so you can also give additional instructions to aptitude here; for instance, aptitude safe-upgrade bash dash-
will attempt to upgrade the bash package and remove the dash package.
It is sometimes necessary to remove one package in order to upgrade another; this command is not able to upgrade packages in such situations.
Use the full-upgrade command to upgrade as many packages as possible.
full-upgrade
Upgrades installed packages to their most recent version, removing or installing packages as necessary. This command is less conservative than
safe-upgrade and thus more likely to perform unwanted actions. However, it is capable of upgrading packages that safe-upgrade cannot upgrade.
If no <package>s are listed on the command line, aptitude will attempt to upgrade every package that can be upgraded. Otherwise, aptitude will
attempt to upgrade only the packages which it is instructed to upgrade. The <package>s can be extended with suffixes in the same manner as
arguments to aptitude install, so you can also give additional instructions to aptitude here; for instance, aptitude full-upgrade bash dash-
will attempt to upgrade the bash package and remove the dash package.
Note
This command was originally named dist-upgrade for historical reasons, and aptitude still recognizes dist-upgrade as a synonym for
full-upgrade.
Вкратце это означает следующее:
safe-upgrade
Обновляет установленные пакеты до последней версии. Не удаляет и не устанавливает пакеты по зависимостям.
full-upgrade
Обновляет установленные пакеты до последней версии. Удаляет и устанавливает пакеты по зависимостям. То есть обновляет систему до следующей версии.
У тебя система превратилась в Runtu XFCE 14.04.3
Для Ubuntu 14.04 обновления будут выпускать до апреля 2019 года, для Runtu так же - так как используются репозитории Ubuntu.