If I had a running debian system, the following command could be issued to get list of installed packages:
dpkg --get-selections > packages.lst But now I have only a full backup of root partition (complete system backup) of the working system and nothing more. How can I generate list of installed packages from these files?
chroot into it, and run dpkg would be the easiest thing. See https://superuser.com/a/417004/20798 for how to get a working /proc, /sys, and /dev inside the chroot.
Since you have a working debian system outside the backup, you could probably just use
dpkg --admindir=dir --get-selections The dir defaults to /var/lib/dpkg, so put the path to your backup's /var/lib/dpkg.
Don't forget that dpkg --get-selections doesn't show which packages were manually installed, and which were only installed to satisfy dependencies (and thus should be auto-removed when no longer needed because newer versions of the packages you actually want have different deps, or because you purge a manually installed package.)
I use aptitude, which makes it easy to mark everything as auto-installed, then go through and mark some packages as manually installed until nothing you want to keep is getting auto-removed. Start with big meta-packages, like build-essential, the Debian equivalents of ubuntu-standard and ubuntu-desktop, and stuff like that. In aptitude, hit r to see the reverse-depends of a package (pkgs that depend on it).
apt-mark or (far more convenient but not installed by default) apt-clone to clone a set of installed packages including the automatic/manual flag. dpkg --admindir=dir --get-selections also lists deinstalled packages and other non-installed ones. You need to parse it to get only installed packages. dpkg --set-selections. In which case, run aptitude before letting dpkg actually act on those selections, and mark all the to-be-uninstalled packages as don't-change. Or go through the list and see which cruft you actually want to purge (and change it from deinstall to purge). Peter's approach is better but you could also just parse /var/lib/dpkg/status which doesn't require a chroot:
$ perl -00ne 'if(/: install/){/Package:\s*(\S+)/ && print "$1\n"}' /var/lib/dpkg/status On my machine, that returned the same list of packages as dpkg --get-selections | awk '$NF=="install"{print $1}' (the awk parsing is needed because otherwise it also shows deinstalled packages).
dpkg --get-selections, 3925 packages according to your one-liner and 1473 packages missing in your one-liner. dpkg --get-selections doesn't list only installed packages. It will also show uninstalled ones. Compare the output of my one-liner to that of dpkg --get-selections | awk '$NF=="install"{print $1}' instead. Alternatively, just run dpkg --get-selections | grep deinstall to see the various packages you don't want listed. dpkg_installed command returns 193 less packages than dpkg --get-selections commad. your one-liner has 1204 additional, 1473 missing packages when compared to dpkg --get-selections command and 1204 additional, 1280 missing packages when compared to dpkg_installed command. dpkg_installed? Where can I get it, it sounds useful and I'd like to check this on my machine. I can tell you that here, dpkg --get-selections | awk '$NF=="install"{print $1}' and the perl one-liner return the same list. In any case, there's no point in comparing it to dpkg --get-selections since that prints various things you don't want. dpkg_installed in place of dpkg --get-selections | awk '$NF=="install"{print $1}'. By the way, I run couple of tests and it seems that there something wrong with my current installation, since I can not find some of my installed applications in dpkg --get-selections list. I'm toggling my downvote till I run these commands on some other installations. You can have a listing using of you packages using :
awk '/Package:/ {print $2}' /var/lib/dpkg/status
