diff --git a/cd.sh b/cd.sh
index cd52fec..e1d5b05 100644
--- a/cd.sh
+++ b/cd.sh
@@ -23,7 +23,7 @@ case "${CD_OS_NAME}" in
 esac
 CD_STEP=0
 
-function step {
+function cd_step {
     if [ "${1}" ] ; then
         ((CD_STEP++))
         echo "
@@ -32,14 +32,29 @@ function step {
     fi
 }
 
-step "set name servers"
-for server in "${CD_DNS_SERVERS[@]}" ; do
-    echo "nameserver ${server}" \
-    >> "${CD_DNS_FILE}" \
-    || exit
-done
+function cd_write {
+local file="${1}"
+local text="${2}"
+    if [ "${file}" ] ; then
+        echo -n "${text}" \
+        > "${file}" \
+        || exit
+    fi
+}
 
-step "configure package manager"
+function cd_set_dns {
+local server
+local text=''
+    cd_step "set name servers"
+    for server in "${CD_DNS_SERVERS[@]}" ; do
+        text+="nameserver ${server}
+"
+    done
+    cd_write "${CD_DNS_FILE}" "${text}" \
+    || exit
+}
+
+cd_step "configure package manager"
 echo -n "\
 Acquire::Check-Valid-Until True;
 APT::Get::Show-Versions True;
@@ -48,7 +63,7 @@ APT::Install-Suggests False;
 Dir::Etc::SourceParts '';
 " > '/etc/apt/apt.conf.d/apt.conf' \
 || exit
-step "configure package repositories"
+cd_step "configure package repositories"
 echo -n "\
 deb https://deb.debian.org/debian bookworm main
 deb https://deb.debian.org/debian bookworm-backports main
@@ -57,45 +72,52 @@ deb https://deb.debian.org/debian-security bookworm-security main
 " > '/etc/apt/sources.list' \
 || exit
 
-step "disable package verification"
+cd_step "disable package verification"
 echo -n "\
 Acquire::https::Verify-Peer False;
 " > '/etc/apt/apt.conf.d/https' \
 || exit
-step "update package catalog"
+cd_step "update package catalog"
 apt-get update \
 || exit
-step "install CA certificates package"
+cd_step "install CA certificates package"
 apt-get install --yes 'ca-certificates' \
 || exit
-step "enable package verification"
+cd_step "enable package verification"
 rm '/etc/apt/apt.conf.d/https' \
 || exit
 
-step "update package catalog"
+cd_step "update package catalog"
 apt-get update \
 || exit
-step "upgrade packages"
+cd_step "upgrade packages"
 apt-get upgrade --yes \
 || exit
 
-step "install Git"
+cd_step "install Git"
 apt-get install --yes 'git' \
 || exit
 
 DIRECTORY="$(mktemp --directory)" \
 || exit
-step "clone Continuous Delivery"
+cd_step "clone Continuous Delivery"
 git clone \
 "${GITHUB_SERVER_URL}/${CD_REPOSITORY}" \
 "${DIRECTORY}" \
 || exit
 
-step "install Python"
+cd_step "install Python"
 apt-get install --yes 'python3' \
 || exit
-step "clean package cache"
+cd_step "clean package cache"
 apt-get clean \
 || exit
-step "bootstrap"
+cd_step "bootstrap"
 "${DIRECTORY}/bootstrap.sh"
+
+
+function cd_main {
+    cd_set_dns
+}
+
+cd_main