diff --git a/shadowsocks-all.sh b/shadowsocks-all.sh
index ce4fa88..b91022d 100644
--- a/shadowsocks-all.sh
+++ b/shadowsocks-all.sh
@@ -490,11 +490,11 @@ install_prepare() {
 }
 
 install_libsodium() {
-    if [ ! -f /usr/local/lib/libsodium.a ]; then
+    if [ ! -f /usr/lib/libsodium.a ]; then
         cd ${cur_dir}
         tar zxf ${libsodium_file}.tar.gz
         cd ${libsodium_file}
-        ./configure && make && make install
+        ./configure --prefix=/usr && make && make install
         if [ $? -ne 0 ]; then
             echo -e "${red}Error:${plain} ${libsodium_file} install failed."
             install_cleanup
@@ -503,17 +503,18 @@ install_libsodium() {
     else
         echo -e "${green}Info:${plain} ${libsodium_file} already installed."
     fi
-
-    echo "/usr/local/lib" > /etc/ld.so.conf.d/local.conf
-    ldconfig
 }
 
 install_mbedtls() {
-    cd ${cur_dir}
-    tar xf ${mbedtls_file}-gpl.tgz
-    cd ${mbedtls_file}
-    make SHARED=1 CFLAGS=-fPIC
-    make install
+    if [ ! -f /usr/lib/libmbedtls.a ]; then
+        cd ${cur_dir}
+        tar xf ${mbedtls_file}-gpl.tgz
+        cd ${mbedtls_file}
+        make SHARED=1 CFLAGS=-fPIC
+        make DESTDIR=/usr install
+    else
+        echo -e "${green}Info:${plain} ${mbedtls_file} already installed."
+    fi
 }
 
 install_shadowsocks_python() {
diff --git a/shadowsocks-libev-debian.sh b/shadowsocks-libev-debian.sh
index 3ba01a9..1ce32d2 100644
--- a/shadowsocks-libev-debian.sh
+++ b/shadowsocks-libev-debian.sh
@@ -254,13 +254,9 @@ pre_install(){
 download_files(){
     cd ${cur_dir}
 
-    if [ -f ${shadowsocks_libev_ver}.tar.gz ]; then
-        echo "${shadowsocks_libev_ver}.tar.gz [found]"
-    else
-        if ! wget --no-check-certificate -O ${shadowsocks_libev_ver}.tar.gz ${download_link}; then
-            echo "Failed to download ${shadowsocks_libev_ver}.tar.gz"
-            exit 1
-        fi
+    if ! wget --no-check-certificate -O ${shadowsocks_libev_ver}.tar.gz ${download_link}; then
+        echo "Failed to download ${shadowsocks_libev_ver}.tar.gz"
+        exit 1
     fi
 
     if ! wget --no-check-certificate -O ${libsodium_file}.tar.gz ${libsodium_url}; then
@@ -305,25 +301,26 @@ EOF
 
 # Install Shadowsocks-libev
 install_shadowsocks(){
-    if [ ! -f /usr/local/lib/libsodium.a ]; then
+    if [ ! -f /usr/lib/libsodium.a ]; then
         cd ${cur_dir}
         tar zxf ${libsodium_file}.tar.gz
         cd ${libsodium_file}
-        ./configure && make && make install
+        ./configure --prefix=/usr && make && make install
         if [ $? -ne 0 ]; then
             echo "${libsodium_file} install failed!"
             exit 1
         fi
     fi
 
-    echo "/usr/local/lib" > /etc/ld.so.conf.d/local.conf
-    ldconfig
+    if [ ! -f /usr/lib/libmbedtls.a ]; then
+        cd ${cur_dir}
+        tar xf ${mbedtls_file}-gpl.tgz
+        cd ${mbedtls_file}
+        make SHARED=1 CFLAGS=-fPIC
+        make DESTDIR=/usr install
+    fi
 
-    cd ${cur_dir}
-    tar xf ${mbedtls_file}-gpl.tgz
-    cd ${mbedtls_file}
-    make SHARED=1 CFLAGS=-fPIC
-    make install
+    ldconfig
 
     cd ${cur_dir}
     tar zxf ${shadowsocks_libev_ver}.tar.gz
diff --git a/shadowsocks-libev.sh b/shadowsocks-libev.sh
index de347fd..7ebe027 100644
--- a/shadowsocks-libev.sh
+++ b/shadowsocks-libev.sh
@@ -253,13 +253,9 @@ pre_install(){
 download_files(){
     cd ${cur_dir}
 
-    if [ -f ${shadowsocks_libev_ver}.tar.gz ]; then
-        echo "${shadowsocks_libev_ver}.tar.gz [found]"
-    else
-        if ! wget --no-check-certificate -O ${shadowsocks_libev_ver}.tar.gz ${download_link}; then
-            echo "Failed to download ${shadowsocks_libev_ver}.tar.gz"
-            exit 1
-        fi
+    if ! wget --no-check-certificate -O ${shadowsocks_libev_ver}.tar.gz ${download_link}; then
+        echo "Failed to download ${shadowsocks_libev_ver}.tar.gz"
+        exit 1
     fi
 
     if ! wget --no-check-certificate -O ${libsodium_file}.tar.gz ${libsodium_url}; then
@@ -338,20 +334,18 @@ firewall_set(){
 
 # Install Shadowsocks-libev
 install_shadowsocks(){
-    if [ ! -f /usr/local/lib/libsodium.a ]; then
+    if [ ! -f /usr/lib/libsodium.a ]; then
         cd ${cur_dir}
         tar zxf ${libsodium_file}.tar.gz
         cd ${libsodium_file}
-        ./configure && make && make install
+        ./configure --prefix=/usr && make && make install
         if [ $? -ne 0 ]; then
             echo "${libsodium_file} install failed!"
             exit 1
         fi
     fi
 
-    echo "/usr/local/lib" > /etc/ld.so.conf.d/local.conf
     ldconfig
-
     cd ${cur_dir}
     tar zxf ${shadowsocks_libev_ver}.tar.gz
     cd ${shadowsocks_libev_ver}