-CHROOT_SCRIPTS='yes'
-CONFFILES='/etc/debootstrap'
-DEBCONF='yes'
-DEBIAN_FRONTEND='noninteractive'
-DEBOOTSTRAP='debootstrap'
-EXTRAPACKAGES='yes'
-FALLBACK_MIRROR='http://cdn.debian.net/debian'
-FORCE=''
-HOSTNAME='grml'
-INITRD='yes'
-INSTALL_NOTES='/etc/debootstrap/install_notes'
-LOCALES='yes'
-MIRROR="$FALLBACK_MIRROR"
-MKFS='mkfs.ext3'
-PACKAGES='yes'
-PRE_SCRIPTS='yes'
-RECONFIGURE='console-data'
-RELEASE='squeeze'
-RM_APTCACHE='yes'
-SCRIPTS='yes'
-SECURE='yes'
-TIMEZONE='Europe/Vienna'
-TUNE2FS='tune2fs -c0 -i0'
-UPGRADE_SYSTEM='yes'
-VMSIZE="2G"
+[ -n "$CHROOT_SCRIPTS" ] || CHROOT_SCRIPTS='yes'
+[ -n "$CONFFILES" ] || CONFFILES='/etc/debootstrap'
+[ -n "$DEBCONF" ] || DEBCONF='yes'
+[ -n "$DEBIAN_FRONTEND" ] || DEBIAN_FRONTEND='noninteractive'
+[ -n "$DEBOOTSTRAP" ] || DEBOOTSTRAP='debootstrap'
+[ -n "$DEFAULT_LOCALES" ] || DEFAULT_LOCALES='en_US.UTF-8'
+[ -n "$EXTRAPACKAGES" ] || EXTRAPACKAGES='yes'
+[ -n "$FALLBACK_MIRROR" ] || FALLBACK_MIRROR='http://http.debian.net/debian'
+[ -n "$FORCE" ] || FORCE=''
+[ -n "$HOSTNAME" ] || HOSTNAME='grml'
+[ -n "$INITRD" ] || INITRD='yes'
+[ -n "$INSTALL_NOTES" ] || INSTALL_NOTES='/etc/debootstrap/install_notes'
+[ -n "$LOCALES" ] || LOCALES='yes'
+[ -n "$MIRROR" ] || MIRROR="$FALLBACK_MIRROR"
+[ -n "$MKFS" ] || MKFS='mkfs.ext4'
+[ -n "$PACKAGES" ] || PACKAGES='yes'
+[ -n "$PRE_SCRIPTS" ] || PRE_SCRIPTS='yes'
+[ -n "$RECONFIGURE" ] || RECONFIGURE='console-data'
+[ -n "$RELEASE" ] || RELEASE='wheezy'
+[ -n "$RM_APTCACHE" ] || RM_APTCACHE='yes'
+[ -n "$SCRIPTS" ] || SCRIPTS='yes'
+[ -n "$SECURE" ] || SECURE='yes'
+[ -n "$TIMEZONE" ] || TIMEZONE='Europe/Vienna'
+[ -n "$TUNE2FS" ] || TUNE2FS='tune2fs -c0 -i0'
+[ -n "$UPGRADE_SYSTEM" ] || UPGRADE_SYSTEM='yes'
+[ -n "$VMSIZE" ] || VMSIZE="2G"
+[ -n "$FIXED_DISK_IDENTIFIERS" ] || FIXED_DISK_IDENTIFIERS="no"