diff --git a/cd.sh b/cd.sh
index 819404e..5f799d4 100644
--- a/cd.sh
+++ b/cd.sh
@@ -1,3 +1,5 @@
+#! /usr/bin/env bash
+
 CD_DNS_SERVERS=(
 '9.9.9.9'
 )
@@ -25,7 +27,7 @@ CD_STEP=0
 
 function cd_step {
     if [ "${1}" ] ; then
-        CD_STEP=$((CD_STEP+1))
+        ((CD_STEP++))
         echo "
  ↕ ${CD_STEP} ↔ ${1}
 "
@@ -42,7 +44,7 @@ local text="${2}"
     fi
 }
 
-function cd_set_dns {
+function cd_set_dns_resolving {
 local server
 local text=''
     cd_step "set name servers"
@@ -54,18 +56,26 @@ local text=''
     || exit
 }
 
-function cd_main {
-    cd_set_dns
-
-cd_step "configure package manager"
-echo -n "\
+function cd_set_packages_configuration {
+    cd_step "configure package manager"
+    case "${CD_OS_NAME}" in
+        'debian')
+    cd_write '/etc/apt/apt.conf.d/apt.conf' "\
 Acquire::Check-Valid-Until True;
 APT::Get::Show-Versions True;
 APT::Install-Recommends False;
 APT::Install-Suggests False;
-Dir::Etc::SourceParts '';
-" > '/etc/apt/apt.conf.d/apt.conf' \
-|| exit
+Dir::Etc::SourceParts \"\";
+"
+        ;;
+        *) exit 1 ;;
+    esac
+}
+
+function cd_main {
+    cd_set_dns_resolving
+    cd_set_packages_configuration
+
 cd_step "configure package repositories"
 echo -n "\
 deb https://deb.debian.org/debian bookworm main