diff --git a/knowledge base/apt.md b/knowledge base/apt.md
index 942d7f4..02516aa 100644
--- a/knowledge base/apt.md	
+++ b/knowledge base/apt.md	
@@ -3,17 +3,77 @@
 ## TL;DR
 
 ```sh
-# mark all packages as non-explicitly installed
-apt-mark auto $(sudo apt-mark showmanual)
+# Update the packages lists.
+sudo apt update
 
-# remove orphaned packages
-apt autoremove --purge
+# Upgrade the system.
+sudo apt upgrade
+sudo apt dist-upgrade
+
+# Look for packages.
+apt search 'ansible'
+apt search --names-only 'python'
+
+# Show details of packages.
+apt show 'vlc'
+
+# List a package's dependencies.
+apt depends 'ufw'
+
+# Install packages.
+sudo apt install 'nano' 'python3-zstd/stable'
+
+# Remove packages.
+sudo apt remove 'dhclient' 'sudo'
+sudo apt remove --purge 'bluez'
+sudo apt purge 'crda'
+
+# Remove orphaned packages.
+sudo apt autoremove --purge
+
+# List packages.
+sudo apt list
+sudo apt list --upgradable
+sudo apt list --installed
+
+# List explicitly installed packages only.
+sudo apt-mark showmanual
+
+# Mark packages as explicitly installed.
+sudo apt-mark manual 'vim' 'unattended-upgrades'
+
+# List non-explicitly installed packages only.
+sudo apt-mark showauto
+
+# Mark packages as non-explicitly installed.
+sudo apt-mark auto 'zsh' 'bash-completion'
+sudo apt-mark auto $(sudo apt-mark showmanual)
+
+# Reconfigure packages.
+sudo dpkg-reconfigure 'mariadb-server'
+```
+
+## Automate security upgrades
+
+Leverage `unattended-upgrades` for this.
+
+```sh
+# Check what packages would be installed.
+sudo unattended-upgrade -d --dry-run
+
+# Run manually.
+sudo unattended-upgrade
 ```
 
 ## Further readings
 
 - [Apt configuration]
 - [Configuring Apt sources]
+- [Unattended Upgrades]
+- [cheat.sh]
 
+<!-- external references -->
 [apt configuration]: https://wiki.debian.org/AptConfiguration
 [configuring apt sources]: https://wiki.debian.org/SourcesList
+[unattended upgrades]: https://wiki.debian.org/UnattendedUpgrades
+[cheat.sh]: