How to create and use a local repository mirror on Ubuntu 9.10. These instructions should work with minor modifications for other versions of Ubuntu.

# File: HOWTO Create a Local Repository Mirror on Ubuntu.notes
# Date: 2010/03/17
# Refs: https://help.ubuntu.com/community/Debmirror
#       http://ubuntuforums.org/archive/index.php/t-599479.html
#       http://www.arsgeek.com/2007/02/14/how-to-set-up-your-own-local-repositories-with-apt-mirror/
#       http://pwet.fr/man/linux/commandes/debmirror
# Desc: How to create a local repository for 
#       Ubuntu 9.10 Karmic Koala.

# -------------------------------------
#           Setup the Server
# -------------------------------------
# Install Ubuntu (I used 9.10) on a machine with plenty of 
# free storage space (I used an 8GB OS vmdk and an 80GB data 
# vmdk used through LVM so that I could easily add/grow to
# it in the future if necessary).

# Create the mirror user, I'll be using ubuntu.
# NOTE: You don't have to add this user to the wheel but if you don't, the steps below that require sudo
#       will require you to run them from an account with root or wheel access and may also require
#       that you change the ownership/group of files/directories afterwards.
sudo useradd -m ubuntu -Gusers,wheel
sudo password ubuntu

# UPDATE 2012/01/30: As Dave points out below, you'll need to create your mirrorkeyring folder with the correct user account.
#                    If you aren't already running as that user, you can change your shell using su
su - ubuntu

# Update your apt-get package listing
sudo apt-get update

# Install debmirror
sudo apt-get install debmirror

# Create the location for the repo data to live
sudo mkdir -P /mirror/ubuntu

# Set the permissions for the repo data
sudo chown -R ubuntu:ubuntu /mirror/ubuntu
sudo chmod -R 771 /mirror/ubuntu

# Setup the keyring for correctly verifying Release signatures
gpg --no-default-keyring --keyring /home/ubuntu/mirrorkeyring/trustedkeys.gpg --import /usr/share/keyrings/ubuntu-archive-keyring.gpg

# Create the mirrorbuild.sh script
vim /home/ubuntu/mirrorbuild.sh

# NOTE: The ubuntu community documentation has you using 
#       the HTTP protocol for the mirror build script
#       however, I prefer rsync because we can rate limit.
#       When the download is going to take days,
#       I'd like to be able to use my connection in
#       the interim.

# --------------------------------------------
# BEGIN MIRRORBUILD.SH SCRIPT
# --------------------------------------------

#!/bin/bash

## Setting variables with explanations.

#
# Don't touch the user's keyring, have our own instead
#
export GNUPGHOME=/home/ubuntu/mirrorkeyring

# Arch=         -a      # Architecture. 
# For Ubuntu can be i386, amd64, powerpc and/or sparc (sparc support begins with dapper)
# 
# Comma separated values
arch=i386,amd64

# Minimum Ubuntu system requires main, restricted
# Section=      -s      # Section
# (One of the following - main/restricted/universe/multiverse).
# You can add extra file with $Section/debian-installer.
# ex: main/debian-installer,universe/debian-installer,multiverse/debian-installer,restricted/debian-installer
section=main,restricted,universe,multiverse

# Release=      -d      # Release of the system
# (Dapper, Edgy, Feisty, Gutsy, Hardy, IntrepidJaunty, Karmic), 
# and the -updates and -security ( -backports can be added if desired)
dist=karmic,karmic-updates,karmic-security

# Server=       -h      # Server name,
# minus the protocol and the path at the end
# CHANGE "*" to equal the mirror you want to create your
# mirror from. au. in Australia  ca. in Canada. This can be 
# found in your own /etc/apt/sources.list file, 
# assuming you have Ubuntu installed.
server=us.archive.ubuntu.com

# Dir=          -r      # Path from the main server,
# so http://my.web.server/$dir, Server dependant
# Lead with a '/' for everything but rsync,
# where we lead with a ':'
inPath=:ubuntu

# Proto=        -e      # Protocol to use for transfer
# (http, ftp, hftp, rsync)
# Choose one - http is most usual the service, and the
# service must be availabee on the server you point at.
# NOTE: debmirror uses -aIL --partial by default.
#       However, if you provide the --rsync-options
#       paramter (which we do) then you HAVE to provide 
#       it -aIL --partial in addition to whatever You
#       want to add (e.g. --bwlimit) If you don't
#       debmirror will exit with thousands of files
#       missing.
proto=rsync
rsyncoptions="-aIL --partial --bwlimit=100"

# Outpath=              # Directory to store the mirror in
# Make this a full path to where you want to mirror the material.
#
outPath=/mirror/ubuntu/

# The --nosource option only downloads debs and not deb-src's
# The --progress option shows files as they are downloaded
# --source \ in the place of --no-source \ if you want sources also.
# --nocleanup  Do not clean up the local mirror after mirroring
# is complete. Use this option to keep older repository
# Start script
#
debmirror       -a $arch \
                --no-source \
                -s $section \
                -h $server \
                -d $dist \
                -r $inPath \
                --progress \
                -e $proto \
                --rsync-options="$rsyncoptions" \
                $outPath

# -----------------------------------------------------
# END BUILDMIRROR.SH SCRIPT 
# -----------------------------------------------------

# Add execute permissions on the mirrorbuild.sh script
chmod +x mirrorbuild.sh

# Run the script
./mirrorbuild.sh

# Go home, kick back, have a beer while it downloads 43GBs 
# (in the case of karmic, karmic-update, karmic-securty for
# i386 and amd64)

# --------------------------------------
#          Setup the mirror
# --------------------------------------
# Install apache2
sudo apt-get install apache2

# Symlink the mirror data into the web root
sudo ln -s /mirror/ubuntu /var/www/ubuntu

# Point your browser at http://localhost/ubuntu and
# you should see your pool!

# -------------------------------------
#        Updating the Repo Mirror
# -------------------------------------
# To update the repo mirror, just execute the mirrorbuild.sh
# script used to initially build it.
./mirrorbuild.sh

# -------------------------------------
#   Configure Clients to Use this Repo
# -------------------------------------
# Update the apt sources list
cd /etc/apt
sudo mv sources.list sources.list.orig
sudo sensible-editor sources.list

# Replace 'mirrorbox' with your server's DNS name 
# (e.g. karmic-repo.test.com)
# -----------------------------------------------------------------------------
# BEGIN SOURCES.LIST
# -----------------------------------------------------------------------------
# Local network mirror sources.
deb http://mirrorbox/ubuntu karmic main restricted universe multiverse
deb http://mirrorbox/ubuntu karmic-updates main restricted universe multiverse
deb http://mirrorbox/ubuntu karmic-security main restricted universe multiverse
# -----------------------------------------------------------------------------
# END SOURCES.LIST
# -----------------------------------------------------------------------------

# Test to see if you are able to pull down updates 
# from the new mirror
sudo apt-get update