diff --git a/functions.sh b/functions.sh
index 68ee286..3ed4c8f 100644
--- a/functions.sh
+++ b/functions.sh
@@ -2,20 +2,32 @@
 
 SCRIPTNAME="$( basename -- "$0" )"
 
+# check : current user is root?
+check_root () {
+    [[ $EUID -eq 0 ]]
+}
+
+# ok if root
 ensure_root () {
-  if [[ $EUID -ne 0 ]]; then
-    echo "This script must be run as root" 
-    exit 1
-  fi
+    if ! check_root; then
+	echo "ERROR : This script must be run as root"
+	exit 1
+    else
+	return 0
+    fi
 }
 
+# ok if non root
 ensure_not_root () {
-  if [[ $EUID -eq 0 ]]; then
-    echo "This script must not be run as root" 
-    exit 1
-  fi
+    if check_root; then
+	echo "ERROR : This script must not be *run* as root"
+	exit 1
+    else
+	return 0
+    fi
 }
 
+# ok if running script from current directory
 ensure_pwd_is_scriptdir () {
   if [[ $PWD != $ABSDIR ]]; then
     echo "Please cd in the script directory before running it :"
@@ -25,22 +37,107 @@ ensure_pwd_is_scriptdir () {
   fi
 }
 
+# make sure systemd directory exists
 ensure_systemd_as_user_dir_exists () {
-  mkdir -p ${HOME}/.config/systemd/user/
+  [[ -d ${HOME}/.config/systemd/user/ ]] || mkdir -p ${HOME}/.config/systemd/user/
 }
 
+# check: systemd unit exists
 check_systemd_unit_exists () {
   systemctl --user cat -- ${1} &> /dev/null
 }
 
+# ok if systemd unit file {1} exists
+ensure_systemd_unit_exists () {
+    if ! check_systemd_unit_exists ${1}; then
+	echo "ERROR : systemd unit ${1} does not exists!"
+	exit 1
+    else
+	return 0
+    fi
+}
+
+# ok if systemd unit file {1} does not exists
+ensure_systemd_unit_not_exists () {
+    if check_systemd_unit_exists ${1}; then
+	echo "ERROR : systemd unit ${1} already exists!"
+	exit 1
+    else
+	return 0
+    fi
+}
+
+# check: systemd unit running
 check_systemd_unit_running () {
   systemctl --user is-active --quiet service ${1}
 }
 
-check_container_exists () {
-  podman container exists ${1}
+# ok if systemd unit {1} is running
+ensure_systemd_unit_running () {
+    if ! check_systemd_unit_running ${1}; then
+	echo "ERROR : systemd unit ${1} is not running!"
+	exit 1
+    else
+	return 0
+    fi
 }
 
-check_container_running () {
-  [[ "podman container inspect -f '{{.State.Status}}' ${1}" != "running" ]]
+# ok if systemd unit {1} is NOT running
+ensure_systemd_unit_not_running () {
+    if check_systemd_unit_running ${1}; then
+	echo "ERROR : systemd unit ${1} is running!"
+	exit 1
+    else
+	return 0
+    fi
+}
+
+# check: container $1 exists?
+check_container_exists () {
+    podman container exists ${1}
+}
+
+# ok if container exists
+ensure_container_exists () {
+    if ! check_container_exists ${1}; then
+	echo "ERROR : container ${1} does not exists"
+	exit 1
+    else
+	return 0
+    fi
+}
+
+# ok if container does not exists
+ensure_container_not_exists () {
+    if check_container_exists ${1}; then
+	echo "ERROR : container ${1} already exists"
+	exit 1
+    else
+	return 0
+    fi
+}
+
+# check: container ${1} is running?
+check_container_running () {
+  [[ "podman container inspect -f '{{.State.Status}}' ${1}" == "running" ]]
+}
+
+# ok if container exists
+ensure_container_running () {
+    if ! check_container_running ${1}; then
+	echo "ERROR : container ${1} is not running"
+	exit 1
+    else
+	return 0
+    fi
+}
+
+# ok if container does not exists
+ensure_container_not_running () {
+    if check_container_running ${1}; then
+	echo "ERROR : container ${1} is running"
+	exit 1
+    else
+	return 0
+    fi
 }