install the same debian packages on another system

Question

How do I export a list of installed Debian packages on a system, and then install those same packages on a new system?

Answer 1

To backup:

sudo dpkg --get-selections > /tmp/dpkglist.txt

To Restore:

sudo dpkg --set-selections < /tmp/dpkglist.txt
sudo apt-get -y update
sudo apt-get dselect-upgrade

Also see this question for additional options and info: http://serverfault.com/questions/737/ubuntu-how-to-setup-a-new-machine-like-an-existing-one

I have the above running in a daily cronjob that checks the dpgklist into SVN as part of our server inventory. This will allow you to keep a reasonable accurate inventory of installed packages across your servers and its easy to do a quick side-by-side diff to see if a server is missing a particular package.

Answer 2

You can also use aptitude for the same. This preserves information about "automatically installed" packages that other methods do not.

Run following on the reference machine

aptitude search -F '%100p' '~i!~M' > package_list

copy package_list to the other machine and run

xargs aptitude --schedule-only install < package_list; aptitude install;

Answer 3

That's a good idea, and you might also set up one server with apt-proxy if you make a habit of this.