How do I export a list of installed Debian packages on a system, and then install those same packages on a new system?
sudo dpkg --get-selections > /tmp/dpkglist.txt
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: 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.
aptitude also satisfies this usecase, and it preserves information about "automatically installed" packages that other methods do not. Run the following on the reference machine:
aptitude search -F '%p' '~i!~M' > package_list
package_list to the other machine and run
xargs aptitude --schedule-only install < package_list; aptitude install;
That's a good idea, and you might also set up one server with apt-proxy if you make a habit of this.
faultyservers answer worked for me only after running a different command as per http://rayslinux.blogspot.de/2012/10/ubuntu-1210-dpkg-warning-package-not-in.html
sudo apt-get install dselect
sudo dselect access
sudo dselect update
Before that running
sudo apt-get dselect-upgrade
dpkg: warning: package not in database at line 302: xfonts-utils
dpkg: warning: found unknown packages; this might mean the available database is outdated, and needs to be updated through a frontend method
pi@FHEM-new:/tmp $ sudo apt-get dselect-upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
I was trying to install the same packages from my old Raspberry Pi (running Raspbian GNU/Linux 7 (wheezy)) on my new Raspberry (Raspbian GNU/Linux 8 (jessie)).