Add a ton of simple improvements to contrib/mkimage/debootstrap, especially comments in the extra files put inside the image

This also adds support for squeeze-lts. :)

Docker-DCO-1.1-Signed-off-by: Andrew Page <admwiggin@gmail.com> (github: tianon)

contrib/mkimage.sh

@@ -6,7 +6,7 @@ mkimg="$(basename "$0")"
 usage() {
 	echo >&2 "usage: $mkimg [-d dir] [-t tag] script [script-args]"
 	echo >&2 "   ie: $mkimg -t someuser/debian debootstrap --variant=minbase jessie"
-	echo >&2 "       $mkimg -t someuser/ubuntu debootstrap --include=ubuntu-minimal trusty"
+	echo >&2 "       $mkimg -t someuser/ubuntu debootstrap --include=ubuntu-minimal --components main,universe trusty"
 	echo >&2 "       $mkimg -t someuser/busybox busybox-static"
 	echo >&2 "       $mkimg -t someuser/centos:5 rinse --distribution centos-5"
 	exit 1

contrib/mkimage/debootstrap

@@ -23,9 +23,14 @@ shift
 # now for some Docker-specific tweaks
 
 # prevent init scripts from running during install/update
-echo >&2 "+ cat > '$rootfsDir/usr/sbin/policy-rc.d'"
+echo >&2 "+ echo exit 101 > '$rootfsDir/usr/sbin/policy-rc.d'"
 cat > "$rootfsDir/usr/sbin/policy-rc.d" <<'EOF'
 #!/bin/sh
+
+# For most Docker users, "apt-get install" only happens during "docker build",
+# where starting services doesn't work and often fails in humorous ways. This
+# prevents those failures by stopping the services from attempting to start.
+
 exit 101
 EOF
 chmod +x "$rootfsDir/usr/sbin/policy-rc.d"
@@ -34,17 +39,25 @@ chmod +x "$rootfsDir/usr/sbin/policy-rc.d"
 (
 	set -x
 	chroot "$rootfsDir" dpkg-divert --local --rename --add /sbin/initctl
-	ln -sf /bin/true "$rootfsDir/sbin/initctl"
+	cp -a "$rootfsDir/usr/sbin/policy-rc.d" "$rootfsDir/sbin/initctl"
+	sed -i 's/^exit.*/exit 0/' "$rootfsDir/sbin/initctl"
 )
 
-# shrink the image, since apt makes us fat (wheezy: ~157.5MB vs ~120MB)
+# shrink a little, since apt makes us cache-fat (wheezy: ~157.5MB vs ~120MB)
 ( set -x; chroot "$rootfsDir" apt-get clean )
 
 # Ubuntu 10.04 sucks... :)
 if strings "$rootfsDir/usr/bin/dpkg" | grep -q unsafe-io; then
 	# force dpkg not to call sync() after package extraction (speeding up installs)
 	echo >&2 "+ echo force-unsafe-io > '$rootfsDir/etc/dpkg/dpkg.cfg.d/docker-apt-speedup'"
-	echo 'force-unsafe-io' > "$rootfsDir/etc/dpkg/dpkg.cfg.d/docker-apt-speedup"
+	cat > "$rootfsDir/etc/dpkg/dpkg.cfg.d/docker-apt-speedup" <<-'EOF'
+	# For most Docker users, package installs happen during "docker build", which
+	# doesn't survive power loss and gets restarted clean afterwards anyhow, so
+	# this minor tweak gives us a nice speedup (much nicer on spinning disks,
+	# obviously).
+
+	force-unsafe-io
+	EOF
 fi
 
 if [ -d "$rootfsDir/etc/apt/apt.conf.d" ]; then
@@ -52,16 +65,36 @@ if [ -d "$rootfsDir/etc/apt/apt.conf.d" ]; then
 	aptGetClean='"rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true";'
 	echo >&2 "+ cat > '$rootfsDir/etc/apt/apt.conf.d/docker-clean'"
 	cat > "$rootfsDir/etc/apt/apt.conf.d/docker-clean" <<-EOF
+		# Since for most Docker users, package installs happen in "docker build" steps,
+		# they essentially become individual layers due to the way Docker handles
+		# layering, especially using CoW filesystems.  What this means for us is that
+		# the caches that APT keeps end up just wasting space in those layers, making
+		# our layers unnecessarily large (especially since we'll normally never use
+		# these caches again and will instead just "docker build" again and make a brand
+		# new image).
+
+		# Ideally, these would just be invoking "apt-get clean", but in our testing,
+		# that ended up being cyclic and we got stuck on APT's lock, so we get this fun
+		# creation that's essentially just "apt-get clean".
 		DPkg::Post-Invoke { ${aptGetClean} };
 		APT::Update::Post-Invoke { ${aptGetClean} };
 
 		Dir::Cache::pkgcache "";
 		Dir::Cache::srcpkgcache "";
+
+		# Note that we do realize this isn't the ideal way to do this, and are always
+		# open to better suggestions (https://github.com/dotcloud/docker/issues).
 	EOF
 
 	# remove apt-cache translations for fast "apt-get update"
-	echo >&2 "+ cat > '$rootfsDir/etc/apt/apt.conf.d/docker-no-languages'"
-	echo 'Acquire::Languages "none";' > "$rootfsDir/etc/apt/apt.conf.d/docker-no-languages"
+	echo >&2 "+ echo Acquire::Languages 'none' > '$rootfsDir/etc/apt/apt.conf.d/docker-no-languages'"
+	cat > "$rootfsDir/etc/apt/apt.conf.d/docker-no-languages" <<-'EOF'
+	# In Docker, we don't often need the "Translations" files, so we're just wasting
+	# time and space by downloading them, and this inhibits that.  For users that do
+	# need them, it's a simple matter to delete this file and "apt-get update". :)
+
+	Acquire::Languages "none";
+	EOF
 fi
 
 if [ -z "$DONT_TOUCH_SOURCES_LIST" ]; then
@@ -76,39 +109,53 @@ if [ -z "$DONT_TOUCH_SOURCES_LIST" ]; then
 	if [ -z "$lsbDist" -a -r "$rootfsDir/etc/debian_version" ]; then
 		lsbDist='Debian'
 	fi
+	# normalize to lowercase for easier matching
+	lsbDist="$(echo "$lsbDist" | tr '[:upper:]' '[:lower:]')"
 	case "$lsbDist" in
-		debian|Debian)
+		debian)
 			# updates and security!
 			if [ "$suite" != 'sid' -a "$suite" != 'unstable' ]; then
 				(
 					set -x
-					sed -i "p; s/ $suite main$/ ${suite}-updates main/" "$rootfsDir/etc/apt/sources.list"
+					sed -i "
+						p;
+						s/ $suite / ${suite}-updates /
+					" "$rootfsDir/etc/apt/sources.list"
 					echo "deb http://security.debian.org $suite/updates main" >> "$rootfsDir/etc/apt/sources.list"
+					# LTS
+					if [ "$suite" = 'squeeze' ]; then
+						head -1 "$rootfsDir/etc/apt/sources.list" \
+							| sed "s/ $suite / ${suite}-lts /" \
+								>> "$rootfsDir/etc/apt/sources.list"
+					fi
 				)
 			fi
 			;;
-		ubuntu|Ubuntu)
-			# add the universe, updates, and security repositories
+		ubuntu)
+			# add the updates and security repositories
 			(
 				set -x
 				sed -i "
-					s/ $suite main$/ $suite main universe/; p;
-					s/ $suite main/ ${suite}-updates main/; p;
-					s/ $suite-updates main/ ${suite}-security main/
+					p;
+					s/ $suite / ${suite}-updates /; p;
+					s/ $suite-updates / ${suite}-security /
 				" "$rootfsDir/etc/apt/sources.list"
 			)
 			;;
-		tanglu|Tanglu)
+		tanglu)
 			# add the updates repository
 			if [ "$suite" != 'devel' ]; then
 				(
 					set -x
-					sed -i "p; s/ $suite main$/ ${suite}-updates main/" "$rootfsDir/etc/apt/sources.list"
+					sed -i "
+						p;
+						s/ $suite / ${suite}-updates /
+					" "$rootfsDir/etc/apt/sources.list"
 				)
 			fi
 			;;
-		steamos|SteamOS)
-			# add contrib and non-free
+		steamos)
+			# add contrib and non-free if "main" is the only component
 			(
 				set -x
 				sed -i "s/ $suite main$/ $suite main contrib non-free/" "$rootfsDir/etc/apt/sources.list"