diff --git a/tools/dev/bash_profile b/tools/dev/bash_profile
index b43ac32..1c449a2 100644
--- a/tools/dev/bash_profile
+++ b/tools/dev/bash_profile
@@ -120,13 +120,17 @@
         export ONOS_INSTANCES=$(env | grep 'OC[0-9]*=' | sort | cut -d= -f2)
         setPrimaryInstance 1 >/dev/null
         cell
+        onos-verify-cell
         ;;
     "return")
         curl -sS -X DELETE "http://$CELL_WARDEN:4321/?user=$(id -un)"
+        unset ONOS_CELL ONOS_NIC ONOS_IP ONOS_APPS ONOS_BOOT_FEATURES
+        unset OCI OCN OCT ONOS_INSTANCES ONOS_FEATURES
+        unset $(env | sed -n 's:\(^OC[0-9]\{1,\}\)=.*:\1 :g p')
         ;;
 
     "status")
-        curl -sS "http://$CELL_WARDEN:4321/"
+        curl -sS "http://$CELL_WARDEN:4321/" | sort
         ;;
 
     "")
diff --git a/tools/test/bin/onos-cell b/tools/test/bin/onos-cell
new file mode 100755
index 0000000..45a68b9
--- /dev/null
+++ b/tools/test/bin/onos-cell
@@ -0,0 +1,9 @@
+#!/bin/bash
+# -----------------------------------------------------------------------------
+# List available ONOS cells configuration.
+# -----------------------------------------------------------------------------
+
+[ ! -d "$ONOS_ROOT" ] && echo "ONOS_ROOT is not defined" >&2 && exit 1
+. $ONOS_ROOT/tools/dev/bash_profile
+
+cell "$@"
\ No newline at end of file
diff --git a/utils/warden/src/main/java/org/onlab/warden/Warden.java b/utils/warden/src/main/java/org/onlab/warden/Warden.java
index b1e4c71..0e09def 100644
--- a/utils/warden/src/main/java/org/onlab/warden/Warden.java
+++ b/utils/warden/src/main/java/org/onlab/warden/Warden.java
@@ -55,7 +55,6 @@
     private static final long TIMEOUT = 10; // 10 seconds
     private static final int MAX_MINUTES = 240; // 4 hours max
     private static final int MINUTE = 60_000; // 1 minute
-    private static final int DEFAULT_MINUTES = 60;
 
     private final File log = new File("warden.log");
 
@@ -158,10 +157,11 @@
         long now = System.currentTimeMillis();
         Reservation reservation = currentUserReservation(userName);
         if (reservation == null) {
+            checkArgument(minutes > 0, "Number of minutes must be positive");
             Set<String> cells = getAvailableCells();
             checkState(!cells.isEmpty(), "No cells are presently available");
             String cellName = ImmutableList.copyOf(cells).get(random.nextInt(cells.size()));
-            reservation = new Reservation(cellName, userName, now, minutes == 0 ? DEFAULT_MINUTES : minutes);
+            reservation = new Reservation(cellName, userName, now, minutes);
         } else if (minutes == 0) {
             // If minutes are 0, simply return the cell definition
             return getCellDefinition(reservation.cellName);