diff --git a/app.py b/app.py
index b4d97d2..9d7f2c9 100644
--- a/app.py
+++ b/app.py
@@ -1,3 +1,4 @@
+import datetime
 from time import sleep
 from flask import Flask, flash, make_response, redirect, send_file, jsonify, request, render_template, url_for
 import db
@@ -19,21 +20,30 @@ ssh_thread = threading.Thread(target=ssh_thread_function)
 ssh_thread.start()
 
 class PingThread(threading.Thread):
-    def __init__(self, ip):
+    def __init__(self, ip, id):
         super(PingThread, self).__init__()
         self.Ip = ip
+        self.Id = id
     def run(self):
-        utils.ping_client(self.ip)
+        if utils.ping_client(self.Ip) == False:
+            date = db.get_image_allocation_time_id(self.Id)
+            if date is None:
+                return
+            delta = datetime.datetime.now() - date
+            if delta.total_seconds()  > 30:
+                db.del_image_allocation_id(self.Id)
+        else:
+            db.update_image_allocation_time(self.Id)
 
 def check_allocation_thread_function():
     while True:
         ids = db.get_image_allocation_all()
         for x in ids:
             ip = db.get_image_allocation_clientip_id(x)
-            ping_thread = PingThread(ip)
+            ping_thread = PingThread(ip, x)
             ping_thread.start()
             
-        sleep(15)
+        sleep(10)
 
 allocation_thread = threading.Thread(target=check_allocation_thread_function)
 allocation_thread.start()
@@ -156,7 +166,21 @@ def add_image():
 
 @app.route("/api/getconf")
 def get_image():
-    filename = db.get_conf_image(request.headers['token'])
+    try:
+        filename = db.get_conf_image(request.headers['token'])
+    except:
+        pass
+    try:
+        date = db.get_image_allocation_time(request.headers['token'])
+        if date is not None:
+            delta = datetime.datetime.now() - date
+            if delta.total_seconds()  > 30:
+                db.del_image_allocation_token(request.headers['token'])
+            else:
+                filename = None
+    except:
+        pass
+
     if filename is None or filename == "":
         filename = "default.squashfs"
         
diff --git a/db.py b/db.py
index caf257f..04ce969 100644
--- a/db.py
+++ b/db.py
@@ -183,6 +183,17 @@ def get_image_allocation_time_imageid(image_id):
         except:
             return None
         
+def get_image_allocation_time_id(id):
+    connect()
+    with get_cur() as cur:
+        cur.execute("""
+            SELECT last_access_time FROM image_allocation WHERE id = %s 
+        """,(id,))
+        try:
+            return cur.fetchone()[0]
+        except:
+            return None
+        
 def get_image_allocation_clientip(token):
     id_image = get_conf_id(token)
     if id_image is None:
@@ -221,4 +232,44 @@ def set_image_allocation(token, client_ip):
             VALUES (%s, %s, NOW())
         """,(id_image,client_ip,))
         conn.commit()
-    return token
\ No newline at end of file
+    return token
+
+def del_image_allocation_token(token):
+    id_image = get_conf_id(token)
+    if id_image is None:
+        return None 
+    
+    connect()
+    with get_cur() as cur:
+        cur.execute("""
+            DELETE FROM image_allocation WHERE id_image = %s 
+        """,(id_image,))
+        try:
+            conn.commit()
+            return True
+        except:
+            return None
+
+def del_image_allocation_id(id):    
+    connect()
+    with get_cur() as cur:
+        cur.execute("""
+            DELETE FROM image_allocation WHERE id = %s 
+        """,(id,))
+        try:
+            conn.commit()
+            return True
+        except:
+            return None
+        
+def update_image_allocation_time(id):    
+    connect()
+    with get_cur() as cur:
+        cur.execute("""
+            UPDATE SET last_access_time = NOW() FROM image_allocation WHERE id = %s 
+        """,(id,))
+        try:
+            conn.commit()
+            return True
+        except:
+            return None
\ No newline at end of file