diff --git a/file/src/main/java/org/apache/zeppelin/file/HDFSFileInterpreter.java b/file/src/main/java/org/apache/zeppelin/file/HDFSFileInterpreter.java
index 3429de0b55a..662d02add81 100644
--- a/file/src/main/java/org/apache/zeppelin/file/HDFSFileInterpreter.java
+++ b/file/src/main/java/org/apache/zeppelin/file/HDFSFileInterpreter.java
@@ -28,6 +28,7 @@
 import java.util.Date;
 import java.util.List;
 import java.util.Properties;
+import java.util.TimeZone;
 
 import org.apache.zeppelin.completer.CompletionType;
 import org.apache.zeppelin.interpreter.InterpreterContext;
@@ -173,7 +174,11 @@ private String listPermission(OneFileStatus fs){
   }
 
   private String listDate(OneFileStatus fs) {
-    return new SimpleDateFormat("yyyy-MM-dd HH:mm").format(new Date(fs.modificationTime));
+    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm");
+    // Format in GMT so the value matches the "GMT" label appended in listOne(),
+    // regardless of the JVM default time zone.
+    sdf.setTimeZone(TimeZone.getTimeZone("GMT"));
+    return sdf.format(new Date(fs.modificationTime));
   }
 
   private String listOne(String path, OneFileStatus fs) {
diff --git a/file/src/test/java/org/apache/zeppelin/file/HDFSFileInterpreterTest.java b/file/src/test/java/org/apache/zeppelin/file/HDFSFileInterpreterTest.java
index 5c9e268e5d4..dc4dcbe5cc8 100644
--- a/file/src/test/java/org/apache/zeppelin/file/HDFSFileInterpreterTest.java
+++ b/file/src/test/java/org/apache/zeppelin/file/HDFSFileInterpreterTest.java
@@ -20,6 +20,7 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNull;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import com.google.gson.Gson;
 
@@ -30,6 +31,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Properties;
+import java.util.TimeZone;
 
 import org.apache.zeppelin.completer.CompletionType;
 import org.apache.zeppelin.interpreter.InterpreterResult;
@@ -183,6 +185,26 @@ void testNoSuchFile() {
     t.close();
   }
 
+  @Test
+  void testListDateFormatsInGmtToMatchLabel() {
+    // ZEPPELIN-6483: the timestamp must be formatted in GMT to match the trailing
+    // "GMT" label, regardless of the JVM default time zone.
+    TimeZone original = TimeZone.getDefault();
+    try {
+      TimeZone.setDefault(TimeZone.getTimeZone("Asia/Seoul"));
+      HDFSFileInterpreter t = new MockHDFSFileInterpreter(new Properties());
+      t.open();
+      InterpreterResult result = t.interpret("ls -l /", null);
+      String out = result.message().get(0).getData();
+      // modificationTime 1438548219672 == 2015-08-02 20:43 GMT (2015-08-03 05:43 in KST)
+      assertTrue(out.contains("2015-08-02 20:43GMT"),
+          "modification time should be shown in GMT to match the label, but was:\n" + out);
+      t.close();
+    } finally {
+      TimeZone.setDefault(original);
+    }
+  }
+
 }
 
 /**
diff --git a/mongodb/src/main/java/org/apache/zeppelin/mongodb/MongoDbInterpreter.java b/mongodb/src/main/java/org/apache/zeppelin/mongodb/MongoDbInterpreter.java
index 54c121fcdff..5521135a391 100644
--- a/mongodb/src/main/java/org/apache/zeppelin/mongodb/MongoDbInterpreter.java
+++ b/mongodb/src/main/java/org/apache/zeppelin/mongodb/MongoDbInterpreter.java
@@ -35,6 +35,7 @@
 import org.apache.commons.lang3.StringUtils;
 import org.apache.zeppelin.interpreter.Interpreter;
 import org.apache.zeppelin.interpreter.InterpreterContext;
+import org.apache.zeppelin.interpreter.InterpreterException;
 import org.apache.zeppelin.interpreter.InterpreterResult;
 import org.apache.zeppelin.interpreter.InterpreterResult.Code;
 import org.apache.zeppelin.scheduler.Scheduler;
@@ -66,13 +67,28 @@ public MongoDbInterpreter(Properties property) {
   }
 
   @Override
-  public void open() {
+  public void open() throws InterpreterException {
     try (final Scanner scanner = new Scanner(MongoDbInterpreter.class.getResourceAsStream("/shell_extension.js"),
             "UTF-8").useDelimiter("\\A")) {
         shellExtension = scanner.next();
     }
-    commandTimeout = Long.parseLong(getProperty("mongo.shell.command.timeout"));
-    maxConcurrency = Integer.parseInt(getProperty("mongo.interpreter.concurrency.max"));
+
+    final String commandTimeoutValue = getProperty("mongo.shell.command.timeout");
+    try {
+      commandTimeout = Long.parseLong(commandTimeoutValue);
+    } catch (NumberFormatException e) {
+      throw new InterpreterException("Invalid value for property "
+          + "'mongo.shell.command.timeout': " + commandTimeoutValue, e);
+    }
+
+    final String maxConcurrencyValue = getProperty("mongo.interpreter.concurrency.max");
+    try {
+      maxConcurrency = Integer.parseInt(maxConcurrencyValue);
+    } catch (NumberFormatException e) {
+      throw new InterpreterException("Invalid value for property "
+          + "'mongo.interpreter.concurrency.max': " + maxConcurrencyValue, e);
+    }
+
     dbAddress = getProperty("mongo.server.host") + ":" + getProperty("mongo.server.port");
     prepareShellExtension();
   }
diff --git a/mongodb/src/test/java/org/apache/zeppelin/mongodb/MongoDbInterpreterTest.java b/mongodb/src/test/java/org/apache/zeppelin/mongodb/MongoDbInterpreterTest.java
index 08991c3a844..cd57db0a96a 100644
--- a/mongodb/src/test/java/org/apache/zeppelin/mongodb/MongoDbInterpreterTest.java
+++ b/mongodb/src/test/java/org/apache/zeppelin/mongodb/MongoDbInterpreterTest.java
@@ -19,6 +19,8 @@
 
 import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertSame;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
 
 import java.io.File;
 import java.io.IOException;
@@ -30,6 +32,7 @@
 import org.apache.commons.io.FileUtils;
 import org.apache.commons.lang3.StringUtils;
 import org.apache.zeppelin.interpreter.InterpreterContext;
+import org.apache.zeppelin.interpreter.InterpreterException;
 import org.apache.zeppelin.interpreter.InterpreterOutput;
 import org.apache.zeppelin.interpreter.InterpreterOutputListener;
 import org.apache.zeppelin.interpreter.InterpreterResult;
@@ -80,7 +83,7 @@ public static void setup() {
   }
 
   @BeforeEach
-  public void init() {
+  public void init() throws InterpreterException {
     buffer = ByteBuffer.allocate(10000);
     props.put("mongo.shell.path", (IS_WINDOWS ? "" : "sh ") + MONGO_SHELL);
     props.put("mongo.shell.command.table.limit", "10000");
@@ -137,6 +140,60 @@ void testBadConf() {
     assertSame(Code.ERROR, res.code());
   }
 
+  @Test
+  void testInvalidCommandTimeout() {
+    props.setProperty("mongo.shell.command.timeout", "not-a-number");
+
+    final InterpreterException e =
+        assertThrows(InterpreterException.class, () -> interpreter.open());
+
+    assertTrue(e.getMessage().contains("mongo.shell.command.timeout"),
+        "The message must name the offending property: " + e.getMessage());
+    assertTrue(e.getMessage().contains("not-a-number"),
+        "The message must show the invalid value: " + e.getMessage());
+    assertTrue(e.getCause() instanceof NumberFormatException,
+        "The original NumberFormatException must be preserved as the cause");
+  }
+
+  @Test
+  void testMissingCommandTimeout() {
+    props.remove("mongo.shell.command.timeout");
+
+    final InterpreterException e =
+        assertThrows(InterpreterException.class, () -> interpreter.open());
+
+    assertTrue(e.getMessage().contains("mongo.shell.command.timeout"),
+        "The message must name the offending property: " + e.getMessage());
+    assertTrue(e.getCause() instanceof NumberFormatException,
+        "The original NumberFormatException must be preserved as the cause");
+  }
+
+  @Test
+  void testEmptyMaxConcurrency() {
+    props.setProperty("mongo.interpreter.concurrency.max", "");
+
+    final InterpreterException e =
+        assertThrows(InterpreterException.class, () -> interpreter.open());
+
+    assertTrue(e.getMessage().contains("mongo.interpreter.concurrency.max"),
+        "The message must name the offending property: " + e.getMessage());
+    assertTrue(e.getCause() instanceof NumberFormatException,
+        "The original NumberFormatException must be preserved as the cause");
+  }
+
+  @Test
+  void testMissingMaxConcurrency() {
+    props.remove("mongo.interpreter.concurrency.max");
+
+    final InterpreterException e =
+        assertThrows(InterpreterException.class, () -> interpreter.open());
+
+    assertTrue(e.getMessage().contains("mongo.interpreter.concurrency.max"),
+        "The message must name the offending property: " + e.getMessage());
+    assertTrue(e.getCause() instanceof NumberFormatException,
+        "The original NumberFormatException must be preserved as the cause");
+  }
+
   @Override
   public void onUpdateAll(InterpreterOutput interpreterOutput) {