diff --git a/cd.sh b/cd.sh
index eb54620..8d3a52c 100644
--- a/cd.sh
+++ b/cd.sh
@@ -1,24 +1,26 @@
 #! /usr/bin/env sh
 
-[ "${CD_DNS}" ] || CD_DNS="\
+# defaults
+CD_DEFAULT_DNS="\
 9.9.9.9 \
 "
+
 CD_PYTHON_MODULES="\
 cd \
 rwx \
 "
 
-# steps
+# main
 cd_main () {
     cd_set_environment
-    cd_set_dns_resolving ${CD_DNS}
+    cd_set_dns_resolving
     cd_set_packages_repositories
     cd_set_packages_configuration
+    cd_write_ca_certificates
     cd_set_https_verification_off
     cd_update_packages_catalog
     cd_install_packages_tools
     cd_install_ca_certificates
-    cd_write_ca_certificates
     cd_update_ca_certificates
     cd_set_https_verification_on
     cd_update_packages_catalog
@@ -30,9 +32,10 @@ cd_main () {
     cd_execute_python_module ${CD_PYTHON_MODULES}
 }
 
-# functions
+# steps
 
 cd_set_environment () {
+local variable
     cd_step "Set environment"
     #
     CD_CA_PACKAGE="ca-certificates"
@@ -42,8 +45,13 @@ cd_set_environment () {
     #
     case "${CD_OS_NAME}" in
         "debian")
+            case "${CD_OS_VERSION}" in
+                "bookworm"|"bullseye") cd_nop ;;
+                *) cd_error_os "CD_OS_VERSION" ;;
+            esac
             CD_PYTHON_PACKAGE="python3"
             CD_PYTHON_PACKAGES="/usr/lib/python3/dist-packages"
+            CD_CA_ROOT="/usr/local/share/ca-certificates"
         ;;
         "alma")
             case "${CD_OS_VERSION}" in
@@ -53,6 +61,7 @@ cd_set_environment () {
                 ;;
                 *) cd_error_os "CD_OS_VERSION" ;;
             esac
+            CD_CA_ROOT="/etc/pki/ca-trust/source/anchors"
         ;;
         *) cd_error_os "CD_OS_NAME" ;;
     esac
@@ -81,30 +90,25 @@ cd_set_environment () {
     CD_PROJECTS_URL="${CD_SERVER_URL}/${CD_PROJECTS_GROUP}"
     CD_PROJECT_URL="${CD_PROJECTS_URL}/${CD_PROJECT_NAME}"
     #
-    echo -n "\
-CD_OS_NAME=${CD_OS_NAME}
-CD_OS_VERSION=${CD_OS_VERSION}
-#
-CD_DNS_FILE=${CD_DNS_FILE}
-#
-CD_PYTHON_COMMAND=${CD_PYTHON_COMMAND}
-CD_PYTHON_PACKAGES=${CD_PYTHON_PACKAGES}
-#
-CD_SERVER_URL=${CD_SERVER_URL}
-CD_PROJECTS_GROUP=${CD_PROJECTS_GROUP}
-CD_PROJECT_NAME=${CD_PROJECT_NAME}
-CD_PROJECT_BRANCH=${CD_PROJECT_BRANCH}
-#
-CD_PROJECTS_URL=${CD_PROJECTS_URL}
-CD_PROJECT_URL=${CD_PROJECT_URL}
-"
+    cd_echo "CD_OS_NAME" "CD_OS_VERSION"
+    cd_split
+    cd_echo "CD_DNS_FILE"
+    cd_split
+    cd_echo "CD_PYTHON_PACKAGE" "CD_PYTHON_PACKAGES" "CD_CA_ROOT"
+    cd_split
+    cd_echo "CD_SERVER_URL" \
+        "CD_PROJECTS_GROUP" "CD_PROJECT_NAME" "CD_PROJECT_BRANCH"
+    cd_split
+    cd_echo "CD_PROJECTS_URL" "CD_PROJECT_URL"
 }
 
 cd_set_dns_resolving () {
 local server
+local servers
 local text=""
     cd_step "Set DNS resolving"
-    for server in "${@}" ; do
+    [ "${CD_DNS}" ] && servers="${CD_DNS}" || servers="${CD_DEFAULT_DNS}"
+    for server in ${servers} ; do
         text="${text}nameserver ${server}
 "
     done
@@ -118,10 +122,10 @@ local file
     case "${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
+deb https://deb.debian.org/debian ${CD_OS_VERSION} main
+deb https://deb.debian.org/debian ${CD_OS_VERSION}-backports main
+deb https://deb.debian.org/debian ${CD_OS_VERSION}-updates main
+deb https://deb.debian.org/debian-security ${CD_OS_VERSION}-security main
 "
         ;;
         "alma")
@@ -129,7 +133,6 @@ deb https://deb.debian.org/debian-security bookworm-security main
             cd_sed "${file}" "|^m|# m|" "|^# b|b|"
             cd_cat "${file}"
         ;;
-        *) cd_error_os "cd_set_packages_repositories" ;;
     esac
 }
 
@@ -147,25 +150,40 @@ Dir::Etc::SourceParts \"\";
 "
         ;;
         "alma") cd_mkdir "/etc/dnf/dnf.conf.d" ;;
-        *) cd_error_os "cd_set_packages_configuration" ;;
     esac
 }
 
+cd_write_ca_certificates () {
+local index
+local text
+    cd_step "Copy CA"
+    cd_mkdir "${CD_CA_ROOT}"
+    index=1
+    eval "text=\${CD_CA_${index}}"
+    while [ "${text}" ] ; do
+        cd_write "${CD_CA_ROOT}/${index}.crt" "${text}"
+        CD_CA=$((CD_CA+1))
+        index=$((index+1))
+        eval "text=\${CD_CA_${index}}"
+    done
+}
+
 cd_set_https_verification_off () {
-    cd_step "Set HTTPS verification off"
-    case "${CD_OS_NAME}" in
-        "debian")
-            cd_write "/etc/apt/apt.conf.d/https" "\
+    if [ "${CD_CA}" ] ; then
+        cd_step "Set HTTPS verification off"
+        case "${CD_OS_NAME}" in
+            "debian")
+                cd_write "/etc/apt/apt.conf.d/https" "\
 Acquire::https::Verify-Peer False;
 "
-        ;;
-        "alma")
-            cd_write "/etc/dnf/dnf.conf.d/https.conf" "\
+            ;;
+            "alma")
+                cd_write "/etc/dnf/dnf.conf.d/https.conf" "\
 sslverify=False
 "
-        ;;
-        *) cd_error_os "cd_set_https_verification_off" ;;
-    esac
+            ;;
+        esac
+    fi
 }
 
 cd_update_packages_catalog () {
@@ -173,7 +191,6 @@ cd_update_packages_catalog () {
     case "${CD_OS_NAME}" in
         "debian") apt-get update || exit ;;
         "alma") dnf makecache || exit ;;
-        *) cd_error_os "cd_update_packages_catalog" ;;
     esac
 }
 
@@ -182,7 +199,6 @@ cd_install_packages_tools () {
     case "${CD_OS_NAME}" in
         "debian") cd_install_package "apt-utils" ;;
         "alma") echo "TODO" ;;
-        *) cd_error_os "cd_install_packages_tools" ;;
     esac
 }
 
@@ -191,41 +207,22 @@ cd_install_ca_certificates () {
     cd_install_package "${CD_CA_PACKAGE}"
 }
 
-cd_write_ca_certificates () {
-local index
-local target
-local text
-    cd_step "Copy CA"
-    case "${CD_OS_NAME}" in
-        "debian") target="/usr/local/share/ca-certificates" ;;
-        "alma") target="/etc/pki/ca-trust/source/anchors" ;;
-        *) cd_error_os "cd_copy_ca" ;;
-    esac
-    index=1
-    eval "text=\${CD_CA_${index}}"
-    while [ "${text}" ] ; do
-        cd_write "${target}/${index}.crt" "${text}"
-        index=$((index+1))
-        eval "text=\${CD_CA_${index}}"
-    done
-}
-
 cd_update_ca_certificates () {
     cd_step "Update CA"
     case "${CD_OS_NAME}" in
         "debian") update-ca-certificates || exit ;;
         "alma") update-ca-trust || exit ;;
-        *) cd_error_os "cd_update_ca" ;;
     esac
 }
 
 cd_set_https_verification_on () {
-    cd_step "Set HTTPS verification on"
-    case "${CD_OS_NAME}" in
-        "debian") cd_rm "/etc/apt/apt.conf.d/https" ;;
-        "alma") cd_rm "/etc/dnf/dnf.conf.d/https.conf" ;;
-        *) cd_error_os "cd_set_https_verification_on" ;;
-    esac
+    if [ "${CD_CA}" ] ; then
+        cd_step "Set HTTPS verification on"
+        case "${CD_OS_NAME}" in
+            "debian") cd_rm "/etc/apt/apt.conf.d/https" ;;
+            "alma") cd_rm "/etc/dnf/dnf.conf.d/https.conf" ;;
+        esac
+    fi
 }
 
 cd_upgrade_packages () {
@@ -233,7 +230,6 @@ cd_upgrade_packages () {
     case "${CD_OS_NAME}" in
         "debian") apt-get upgrade --assume-yes || exit ;;
         "alma") dnf upgrade --assumeyes || exit ;;
-        *) cd_error_os "cd_upgrade_packages" ;;
     esac
 }
 
@@ -252,7 +248,6 @@ cd_clean_packages_cache () {
     case "${CD_OS_NAME}" in
         "debian") apt-get clean || exit ;;
         "alma") dnf clean all || exit ;;
-        *) cd_error_os "cd_clean_packages_cache" ;;
     esac
 }
 
@@ -265,8 +260,9 @@ local url
     root="$(mktemp --directory)" || exit
     echo "${root}"
     for repository in "${@}" ; do
+        cd_split
         url="${CD_PROJECTS_URL}/${repository}"
-        echo -n "
+        echo -n "\
 ${url}
 ↓
 "
@@ -283,6 +279,7 @@ ${CD_PYTHON_PACKAGES}
         "${path}" "${CD_PYTHON_PACKAGES}" \
         || exit
     done
+    cd_split
     cd_rm "${root}"
 }
 
@@ -298,21 +295,33 @@ ${1}
     "${CD_PYTHON_COMMAND}" -m "${1}" "${CD_STEP}" "${self}"
 }
 
-# tools
+# functions
 
 cd_cat () {
     if [ -f "${1}" ] ; then
-        echo " ↙ $(realpath "${1}")"
+        echo "╭╴$(realpath "${1}")"
         cat "${1}" || exit
     fi
 }
 
+cd_echo () {
+local name
+    if [ "${1}" ] ; then
+        for name in "${@}" ; do
+            eval "echo ${name}=\${${name}}"
+        done
+    fi
+}
+
 cd_error_ci () {
     echo "× CI: ${1}"
     exit 1
 }
+
 cd_error_os () {
-    echo "× OS: ${1}"
+local variable="${1}"
+    echo -n "× OS: "
+    cd_echo "${variable}"
     exit 2
 }
 
@@ -321,7 +330,6 @@ cd_install_package () {
         case "${CD_OS_NAME}" in
             "debian") apt-get install --assume-yes "${1}" || exit ;;
             "alma") dnf install --assumeyes "${1}" || exit ;;
-            *) exit 1 ;;
         esac
     fi
 }
@@ -333,6 +341,8 @@ cd_mkdir () {
     fi
 }
 
+cd_nop () { true ; }
+
 cd_rm () {
     if [ -e "${1}" ] ; then
         echo "← $(realpath "${1}")"
@@ -373,12 +383,10 @@ cd_write () {
 local file="${1}"
 local text="${2}"
     if [ "${file}" ] ; then
-        echo -n "${text}" \
-        > "${file}" \
-        || exit
+        echo -n "${text}" > "${file}" || exit
         cd_cat "${file}"
     fi
 }
 
-# main
+# run
 cd_main
diff --git a/readme.md b/readme.md
index 95f9c4b..f2dcd3e 100644
--- a/readme.md
+++ b/readme.md
@@ -9,6 +9,12 @@
   * [X] ForgeJo / Gitea / GitHub
   * [X] GitLab
 
+## How
+
+### Variables
+
+| CD_DNS | Space separated servers |
+
 ## Tasks
 
 * use constants for OS names