Sometimes you need to know to which debian or ubuntu package a specific file belongs, e.g. because you deleted a system file and want to reinstall it. There is a handy utility called apt-file which searches for a filename in all debian packages.
Installation
apt-get install apt-file
Usage example
search for the file /etc/sysctl.conf
apt-file search /etc/sysctl.conf
result:
apt-file search /etc/sysctl.conf
procps: /etc/sysctl.conf
mypc:~#
Now we see that the file is part of the debian / ubuntu package with the name "procps".