apt-get en el servidor

El apt-get para actualizar el servidor Ubuntu funciona igual que en el sobremesa, solo que deberemos de tener más cuidado, ya que si se rompiera algo (y eso puede ser muy probable) nuestra web crítica de comercio electrónico iría al traste.  Idealmente podemos tener un servidor de test donde poder probar las compatibilidades con las nuevas versiones.

Los comandos más utilizados:

sudo apt-get update        # Trae la lista de actualizaciones
sudo apt-get upgrade       # Actualiza los paquetes instalados y nada más
sudo apt-get dist-upgrade  # Instala actualizaciones (nuevas versiones y resuelve conflictos)
sudo apt-get do-release-upgrade  #Actualiza sistema operativo, peligroso en servidor
sudo apt-get autoclean

Normalmente en un servidor trabajaremos con una versión LTS que dura bastante tiempo, las actualizaciones de sistema operativo suele dar problemas por lo que son las que debemos probar su compatibilidad previamente.

También utilizo la opción ‘-s’ de ‘simular’ para que muestre lo que apt-get va a hacer.

En la documentación de apt-get:

update

update is used to resynchronize the package index files from their sources. The indexes of available packages are fetched from the location(s) specified in /etc/apt/sources.list. For example, when using a Debian archive, this command retrieves and scans the Packages.gz files, so that information about new and updated packages is available. An update should always be performed before an upgrade or dist-upgrade. Please be aware that the overall progress meter will be incorrect as the size of the package files cannot be known in advance.

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. 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 packages.

-s, --simulate, --just-print, --dry-run, --recon, --no-act

No action; perform a simulation of events that would occur but do not actually change the system. Configuration Item: APT::Get::Simulate.

Simulated runs performed as a user will automatically deactivate locking (Debug::NoLocking), and if the option APT::Get::Show-User-Simulation-Note is set (as it is by default) a notice will also be displayed indicating that this is only   simulation. Runs performed as root do not trigger either NoLocking or the notice – superusers should know what they are doing without further warnings from apt-get.

Simulated runs print out a series of lines, each representing a dpkg operation: configure (Conf), remove (Remv) or unpack (Inst). Square brackets indicate broken packages, and empty square brackets indicate breaks that are of no consequence (rare).

Documentación sobre el do-release-upgrade:
La manera recomendada de actualizar una instalación de una Edición Servidor es usar la utilidad do-release-upgrade, que forma parte del paqueteupdate-manager-core, no tiene dependencias gráficas y se instala de forma predeterminada.
Los sistemas basados en Debian también pueden actualizarse usando apt-get dist-upgrade. Sin embargo, se recomienda usar do-release-upgrade porque tiene la habilidad de manejar cambios en la configuración del sistema que algunas veces son necesarios entre diferentes versiones.
Para actualizar a la versión más reciente, introduzca en un terminal:

do-release-upgrade