Fixing Kali Linux Not Updating

The first thing after installing a fresh version of Kali Linux is to run this command line 

  
    sudo apt-get install && apt-get upgrade -y
apt-install will download the necessary files into your machine.
apt-get upgrade will insall them on your machine

KALI LINUX PROPER SOURCES.LIST

You can find the official list of repositories from the Kali's offical website
https://www.kali.org/docs/general-use/kali-linux-sources-list-repositories/

Make sure you have the coorect repositories in place, so it fetch from the right sources.
You can check cthat by running the following command

  
  grep -v '#' /etc/apt/sources.list | sort -u
The result from the command should be the following: 
  
deb http://http.kali.org/kali kali-rolling main contrib non-free non-free-firmware

ERROR RUNNING APT-GET UPDATE

  
    root@kali-pentest:~# apt update
Get:1 http://mirrors.ocf.berkeley.edu/kali kali-rolling InRelease [30.5 kB]
Err:1 http://mirrors.ocf.berkeley.edu/kali kali-rolling InRelease
  The following signatures were invalid: EXPKEYSIG ED444FF07D8D0BF6 Kali Linux Repository 
Fetched 30.5 kB in 1s (25.4 kB/s)
Reading package lists... Done
Building dependency tree       
Reading state information... Done
167 packages can be upgraded. Run 'apt list --upgradable' to see them.
W: An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: http://mirrors.ocf.berkeley.edu/kali kali-rolling InRelease: The following signatures were invalid: EXPKEYSIG ED444FF07D8D0BF6 Kali Linux Repository 
W: Failed to fetch http://http.kali.org/kali/dists/kali-rolling/InRelease  The following signatures were invalid: EXPKEYSIG ED444FF07D8DXK21 Kali Linux Repository

The problem here which is clearly stated in the error message is that the GPG key ED444FF07D8DXK21 is invalid. This issue can be easily resolved. Simply add the invalid signature to your GPG key store.
The SKS Keyserver Network is being deprecated and probably gone by now. Just use another GPG key server like:

  • keyserver.ubuntu.com
  • keys.openpgp.org
  • pgp.mit.edu
  
    gpg --keyserver pgp.mit.edu --recv-key ED444FF07D8DXK21