List all installed packages in Ubuntu

To get a list of packages installed locally do this in your terminal:

dpkg --get-selections | grep -v deinstall

To save that list to a text file called packages on your desktop do this in your terminal:

dpkg --get-selections | grep -v deinstall > ~/Desktop/packages

(you don't need to run this as the superuser, so no sudo necessary here)

Create a backup of what packages are currently installed:

dpkg --get-selections > list.txt

Then (on another system) restore installations from that list:

dpkg --clear-selections
sudo dpkg --set-selections < list.txt

To get rid of stale packages

sudo apt-get autoremove

To get installed like at backup time (i.e. to install packages set by `dpkg --set-selections`)

sudo apt-get dselect-upgrade

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