Only overwrite with a tarball if we haven't already set up an install

gentoostrap.sh

@@ -104,6 +104,8 @@ build-gentoo() {
 		chmod 0600 "$file"
 	done
 	# We grab the checksums first to verify the integrity of any tarball leftover from a previous run
+	local shouldextract=1
+	[ -f "$_optdest/bin/bash" ] && unset shouldextract
 	log "Downloading stage3 signature"
 	curl -s "$stage3.DIGESTS" -o "$stage3sig"
 	if ! [ -f "$stage3file" ]; then
@@ -117,8 +119,11 @@ build-gentoo() {
 	if ! grep "$stage3sig" -e "$(sha512sum "$stage3file" | awk '{print $1}')" > /dev/null 2>&1; then
 		error "stage3 checksum verification failed" 50
 	fi
+	if [ -n "$shouldextract" ]; then
 		log "Decompressing tarball; this will prompt for root privileges"
 		sudo tar xf "$stage3file" -C "$_optdest"
+	fi
+	unset shouldextract
 
 	# Now we do some pre-chroot configuration
 	pushd "$_optdest" > /dev/null 2>&1