diff --git a/cd b/cd
deleted file mode 100644
index 2db24e9..0000000
--- a/cd
+++ /dev/null
@@ -1,5 +0,0 @@
-echo 'nameserver 9.9.9.9' > '/etc/resolv.conf' \
-&& apt-get update \
-&& apt-get install --yes 'git' \
-&& git clone "${GITHUB_SERVER_URL}/rwx.work/cd" '/usr/local/sbin' \
-&& cd-bootstrap
diff --git a/cd-bootstrap b/cd-bootstrap
deleted file mode 100755
index 85c1259..0000000
--- a/cd-bootstrap
+++ /dev/null
@@ -1,20 +0,0 @@
-# ssh
-
-mkdir --parents ~/.ssh
-
-echo "${CD}" > ~/.ssh/id_ed25519
-unset CD
-chmod 400 ~/.ssh/id_ed25519
-
-echo -n "\
-|1|BcccCTMLpM9HHSgJmPu/FFOwOv0=|+3BKK02xibpCPxQ9Nghi2GbXLng= \
-ssh-ed25519 \
-AAAAC3NzaC1lZDI1NTE5AAAAIPHCNcgHlQoiNTXfnUZYvHz9OZwYsmBCrSSV7a7Zche5
-" > ~/.ssh/known_hosts
-
-# packages
-
-apt-get install --yes \
-'python3' \
-'rsync' \
-'tree' \
diff --git a/cd-bootstrap.sh b/cd-bootstrap.sh
new file mode 100755
index 0000000..dbab7b6
--- /dev/null
+++ b/cd-bootstrap.sh
@@ -0,0 +1,27 @@
+KEY_ALGORITHM='ed25519'
+KEY_DIRECTORY='.ssh'
+KEY_PATH="${KEY_DIRECTORY}/id_${KEY_ALGORITHM}"
+KEY_PUBLIC='AAAAC3NzaC1lZDI1NTE5AAAAIPHCNcgHlQoiNTXfnUZYvHz9OZwYsmBCrSSV7a7Zche5'
+PACKAGES=(
+'python3'
+'rsync'
+'tree'
+)
+SERVER="$(basename ${GITHUB_SERVER_URL})"
+
+# ssh
+cd \
+|| exit
+mkdir "${KEY_DIRECTORY}" \
+|| exit
+echo "${CD}" > "${KEY_PATH}" \
+|| exit
+unset CD
+chmod '400' "${KEY_PATH}" \
+|| exit
+echo "${SERVER} ssh-${KEY_ALGORITHM} ${KEY_PUBLIC}" \
+> "${KEY_DIRECTORY}/known_hosts" \
+|| exit
+
+# packages
+apt-get install --yes "${PACKAGES[@]}"
diff --git a/cd.sh b/cd.sh
new file mode 100644
index 0000000..583d97d
--- /dev/null
+++ b/cd.sh
@@ -0,0 +1,27 @@
+NAMESERVERS=(
+'9.9.9.9'
+)
+PACKAGES=(
+'git'
+)
+REPOSITORY='rwx.work/cd'
+TARGET='/usr/local/sbin'
+
+for nameserver in "${NAMESERVERS[@]}" ; do
+    echo "nameserver ${nameserver}" \
+    >> '/etc/resolv.conf' \
+    || exit
+done
+
+apt-get update \
+|| exit
+
+apt-get install --yes "${PACKAGES[@]}" \
+|| exit
+
+git clone \
+"${GITHUB_SERVER_URL}/${REPOSITORY}" \
+"${TARGET}" \
+|| exit
+
+cd-bootstrap.sh