Never forget:

• :w !sudo tee %
  Save a file in vim when you neglected to open the file with sudo but already made changes you don't want to lose.

• Ctrl+X,*
  Evaluate globbing on your current input on the bash command line.

• postfix flush
  Pump out the postfix queue on your backup MX after you've fixed the issue with your primary MX.

• git tag -l | xargs -n 1 git push --delete origin; git tag | xargs git tag -d
  Delete all tags from a git repo - remotely and locally.

• sudo apt-get purge $(for tag in "linux-image" "linux-headers"; do dpkg-query -W -f'${Package}\n' "$tag-[0-9]*.[0-9]*.[0-9]*" | sort -V | awk 'index($0,c){exit} //' c=$(uname -r | cut -d- -f1,2); done)
  Delete old kernels

• https://signup.microsoft.com/productkeystart
  Register new Office 365 product keys for an existing tenant.