diff --git a/cd.sh b/cd.sh
index c362a84..618fc4d 100644
--- a/cd.sh
+++ b/cd.sh
@@ -1,14 +1,33 @@
-NAMESERVERS=(
+CD_DNS_SERVERS=(
 '9.9.9.9'
 )
-REPOSITORY='rwx.work/cd'
+CD_REPOSITORY='rwx.work/cd'
+
+CD_DNS_FILE='/etc/resolv.conf'
+case "${CD_OS_NAME}" in
+    'debian')
+        case "${CD_OS_VERSION}" in
+            'bookworm')
+                echo 'bookworm!'
+            ;;
+            *)
+                echo 'CD_OS_VERSION'
+                exit 2
+            ;;
+        esac
+    ;;
+    *)
+        echo 'CD_OS_NAME'
+        exit 1
+    ;;
+esac
 
 echo "
  1/14 set name servers
 "
-for nameserver in "${NAMESERVERS[@]}" ; do
-    echo "nameserver ${nameserver}" \
-    >> '/etc/resolv.conf' \
+for server in "${CD_DNS_SERVERS[@]}" ; do
+    echo "nameserver ${server}" \
+    >> "${CD_DNS_FILE}" \
     || exit
 done
 
@@ -80,7 +99,7 @@ echo "
 11/14 clone Continuous Delivery
 "
 git clone \
-"${GITHUB_SERVER_URL}/${REPOSITORY}" \
+"${GITHUB_SERVER_URL}/${CD_REPOSITORY}" \
 "${DIRECTORY}" \
 || exit