Aptitude stuff

aptitude search mysql       # Look for something
dpkg -S `which tsclient`    # What package does it belong to?
dpkg -L aria2c              # What does this package provide?
dpkg -i *.deb               # Install a deb file
dpkg -s nodejs              # Show info

dpkg --get-selections       # list installed packages

Apt archives path

/var/cache/apt/archives

List services

service --status-all