diff --git a/cd.sh b/cd.sh
index 5f799d4..6ffb0c3 100644
--- a/cd.sh
+++ b/cd.sh
@@ -56,11 +56,26 @@ local text=''
     || exit
 }
 
+function cd_set_packages_repositories {
+    cd_step "configure package repositories"
+    case "${CD_OS_NAME}" in
+        'debian')
+            cd_write '/etc/apt/sources.list' "\
+deb https://deb.debian.org/debian bookworm main
+deb https://deb.debian.org/debian bookworm-backports main
+deb https://deb.debian.org/debian bookworm-updates main
+deb https://deb.debian.org/debian-security bookworm-security main
+"
+        ;;
+        *) exit 1 ;;
+    esac
+}
+
 function cd_set_packages_configuration {
     cd_step "configure package manager"
     case "${CD_OS_NAME}" in
         'debian')
-    cd_write '/etc/apt/apt.conf.d/apt.conf' "\
+            cd_write '/etc/apt/apt.conf.d/apt.conf' "\
 Acquire::Check-Valid-Until True;
 APT::Get::Show-Versions True;
 APT::Install-Recommends False;
@@ -74,17 +89,9 @@ Dir::Etc::SourceParts \"\";
 
 function cd_main {
     cd_set_dns_resolving
+    cd_set_packages_repositories
     cd_set_packages_configuration
 
-cd_step "configure package repositories"
-echo -n "\
-deb https://deb.debian.org/debian bookworm main
-deb https://deb.debian.org/debian bookworm-backports main
-deb https://deb.debian.org/debian bookworm-updates main
-deb https://deb.debian.org/debian-security bookworm-security main
-" > '/etc/apt/sources.list' \
-|| exit
-
 cd_step "disable package verification"
 echo -n "\
 Acquire::https::Verify-Peer False;