diff --git a/scripts/testbed_cron.sh b/scripts/testbed_cron.sh
index 5491a68..c9f299b 100755
--- a/scripts/testbed_cron.sh
+++ b/scripts/testbed_cron.sh
@@ -2,8 +2,14 @@
 set -ex
 THIS_DIR=$( cd "$( dirname "${BASH_SOURCE[0]:-${(%):-%x}}" )" && pwd )
 
+check_username() {
+    ( echo $1 | grep -qxE "^[a-z][-a-z0-9_]*\$" ) || return 1
+    return 0
+}
+
 touch_user() {
     test -n "$1"
+    check_username $1 || { echo "Invalid user name $1 !"; exit -1; }
     if id -u $1 1>/dev/null 2>&1; then
         return
     fi
@@ -12,13 +18,8 @@ touch_user() {
         exit 1
     fi
 
-    adduser \
-        --shell /bin/bash \
-        --disabled-password \
-        --home /home/$1 \
-        --gecos "nasp member" \
-        $1
-    usermod -a -G nasp $1
+    useradd -m --groups nasp $1
+    su - $1 -c "true"
 
     mkdir -p /home2/$1
     chown $1: /home2/$1