xpro.se

If you get error:

# apt update
...
W: GPG error: ...repositories... Release: The following signatures were invalid: EXPKEYSIG [KEY]

you can list expired keys:

sudo apt-key list | grep "expired: "

and then try to get new keys:

sudo apt-key adv --keyserver keys.gnupg.net --recv-keys [KEY]

Ref: https://askubuntu.com/questions/650032/gpg-errorthe-following-signatures-were-invalid-keyexpired

Tip howto list 3:rd party apps/program/software in Debian 8:

 sudo aptitude search "~o"

Here it is a sample output

i A gcc-4.7-base - GCC, the GNU Compiler Collection (base package)
id  libdb4.7     - Berkeley v4.7 Database Libraries [runtime]
i   libudev0     - libudev shared library

The first character of each line indicates the current state of the package. The most common states are:

• p, meaning that no trace of the package exists on the system,
• c, meaning that the package was deleted but its configuration files remain on the system,
• i, meaning that the package is installed, and
• v, meaning that the package is virtual.

The second character indicates the stored action to be performed on the package, if any, otherwise a blank space is displayed. The most common actions are:

• i, meaning that the package will be installed,
• d, meaning that the package will be deleted, and
• p, meaning that the package and its configuration files will be removed.

If the third character is A, the package was automatically installed.

For a complete list of the possible state and action flags, see the section Accessing Package Information in the aptitude reference guide.

Ref: https://askubuntu.com/questions/98223/how-do-i-get-a-list-of-obsolete-packages