When running apt-get update with a lot of sources in your sources.list, you may encounter this error:
Reading package lists... Error!
E: Dynamic MMap ran out of room
Add this line APT::Cache-Limit "25165824"; to your /etc/apt/apt.conf, and run apt-get update again.
apt-get -o DPkg::options::=--force-confmiss --reinstall install <package>
Update: apt-get only reinstalls missing config files. You can use dpkg --purge <package> to remove the config files before reinstalling the package.
You run apt-get update, and it complains about some missing key IDs:
W: There is no public key available for the following key IDs:
B5D0C804ADB11277
W: GPG error: http://volatile.debian.org etch/volatile Release: The following signatures couldn’t be verified because the public key is not available: NO_PUBKEY EC61E0B0BBE55AB3
W: You may want to run apt-get update to correct these problems
B5D0C804ADB11277 and EC61E0B0BBE55AB3 are the missing gpg pub keys. Fetch them with gpg, and import them into apt :
gpg --keyserver subkeys.pgp.net --recv-key B5D0C804ADB11277
gpg -a --export B5D0C804ADB11277 | apt-key add -
apt-get update
OR (new and improved!)
apt-key advanced --keyserver subkeys.pgp.net --recv-keys B5D0C804ADB11277
apt-get update
or, with a different server: apt-key advanced --keyserver pgp.mit.edu --recv-keys