Fix bug.

install_nginx.sh

@@ -6,6 +6,9 @@ ubuntu_ver="$(lsb_release -rs)"
 sudo apt install -y make
 org_pwd="$(pwd)"
 cpu_cores="$(nproc --all)"
+if [[ -z "$cpu_cores" ]]; then
+    cpu_cores="1"
+fi
 openssl_ver="$(openssl version|xargs| awk '{print $2}')"
 openssl_dir=""
 openssl_source_dir=""