===== Create a repository to update an offline system  =====

When running a Debian system (Debian, Ubuntu, Cumulus, ...) without internet connection, it cannot receive upgrades with ''apt update && apt upgrade -y''\\
But with any Debian based system that is online, it is possible to download the required packages and dependencies (!).

Maybe the source for the latest required repository changed. Therefore, it might be needed to update /etc/apt/sources.list

''apt-get dist-upgrade'' is adding and removing packages if necessary - that doesn't matter on the online system when creating the repository, but it might be important on the offline system:
try on a non-production system first. Using ''apt-get upgrade'' on the offline system will not add nor remove packages but "hold back" (not update) packages that require to add or remove not installed packages. 

Create the required directory structure on the online and offline system

<code bash>
mkdir /var/spool/repo-offline
mkdir /var/spool/repo-offline/archives
mkdir /var/spool/repo-offline/archives/partial
mkdir /var/spool/repo-offline/lists
mkdir /var/spool/repo-offline/lists/partial
mkdir /var/spool/repo-offline/<preferences.d>
mkdir /var/spool/repo-offline/<apt.conf.d>
</code>
Copy following files from the offline system to /var/spool/repo-offline/ on the online system (note /etc/apt/trusted.gpg.d/ is the whole directory)

<code bash>
/etc/apt/trusted.gpg.d/
/etc/apt/sources.list
/etc/apt/trusted.gpg
/var/lib/dpkg/status
</code>

On the **offline** system create the file ''/var/spool/repo-offline/apt.conf''
<code bash>
cat > /var/spool/repo-offline/apt.conf
APT
{
  Get::Download-Only "false";
};

Dir
{
  /* point to the file containing the current versions */
  State "/var/lib/dpkg/";
  State::status "status";

  /* set cache location */
  Cache::archives "/var/spool/repo-offline/archives/";

  /* point to the configuration directory */
  Etc "/var/spool/repo-offline/";
};
</code>

Close cat with <CTRL-d>

On the **online** system create a similar file ''/var/local/repo-offline/apt.conf''
<code bash>
cat > /var/spool/repo-offline/apt.conf
APT
{
  Get::Download-Only "true";
};

Dir
{
  /* point to the file containing the current versions */
  State "/var/spool/repo-offline/";
  State::status "status";

  /* set cache location */
  Cache::archives "/var/spool/repo-offline/archives/";

  /* point to the configuration directory */
  Etc "/var/spool/repo-offline/";
};

</code>
Close cat with <CTRL-d>
==== Create the repository on the online system ====

<code bash>
export APT_CONFIG="</var/spool/repo-offline/apt.conf>"
apt-get update
apt-get --no-download dist-upgrade
</code>

When apt is finished downloading, copy the whole directory /var/local/repo-offline/, **except** the files ''**apt.conf**'' and ''status'' to the offline system
==== Upgrade the offline system ====
<code bash>
export APT_CONFIG="</var/spool/repo-offline/apt.conf>"
apt-get check
apt-get dist-upgrade
</code>