diff --git a/charmhelpers/cli/hookenv.py b/charmhelpers/cli/hookenv.py
new file mode 100644
index 0000000..265c816
--- /dev/null
+++ b/charmhelpers/cli/hookenv.py
@@ -0,0 +1,23 @@
+# Copyright 2014-2015 Canonical Limited.
+#
+# This file is part of charm-helpers.
+#
+# charm-helpers is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3 as
+# published by the Free Software Foundation.
+#
+# charm-helpers is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the GNU Lesser General Public License
+# along with charm-helpers.  If not, see <http://www.gnu.org/licenses/>.
+
+from . import cmdline
+from charmhelpers.core import hookenv
+
+
+cmdline.subcommand('relation-id')(hookenv.relation_id._wrapped)
+cmdline.subcommand('service-name')(hookenv.service_name)
+cmdline.subcommand('remote-service-name')(hookenv.remote_service_name._wrapped)
diff --git a/charmhelpers/core/host.py b/charmhelpers/core/host.py
index f656b85..ec659ee 100644
--- a/charmhelpers/core/host.py
+++ b/charmhelpers/core/host.py
@@ -148,6 +148,16 @@ def adduser(username, password=None, shell='/bin/bash', system_user=False):
     return user_info
 
 
+def user_exists(username):
+    """Check if a user exists"""
+    try:
+        pwd.getpwnam(username)
+        user_exists = True
+    except KeyError:
+        user_exists = False
+    return user_exists
+
+
 def add_group(group_name, system_group=False):
     """Add a group to the system"""
     try:
@@ -280,6 +290,17 @@ def mounts():
     return system_mounts
 
 
+def fstab_mount(mountpoint):
+    """Mount filesystem using fstab"""
+    cmd_args = ['mount', mountpoint]
+    try:
+        subprocess.check_output(cmd_args)
+    except subprocess.CalledProcessError as e:
+        log('Error unmounting {}\n{}'.format(mountpoint, e.output))
+        return False
+    return True
+
+
 def file_hash(path, hash_type='md5'):
     """
     Generate a hash checksum of the contents of 'path' or None if not found.
diff --git a/charmhelpers/core/services/helpers.py b/charmhelpers/core/services/helpers.py
index 8005c41..3f67783 100644
--- a/charmhelpers/core/services/helpers.py
+++ b/charmhelpers/core/services/helpers.py
@@ -16,7 +16,9 @@
 
 import os
 import yaml
+
 from charmhelpers.core import hookenv
+from charmhelpers.core import host
 from charmhelpers.core import templating
 
 from charmhelpers.core.services.base import ManagerCallback
@@ -240,27 +242,41 @@ class TemplateCallback(ManagerCallback):
 
     :param str source: The template source file, relative to
         `$CHARM_DIR/templates`
+
     :param str target: The target to write the rendered template to
     :param str owner: The owner of the rendered file
     :param str group: The group of the rendered file
     :param int perms: The permissions of the rendered file
-
+    :param partial on_change_action: functools partial to be executed when
+                                     rendered file changes
     """
     def __init__(self, source, target,
-                 owner='root', group='root', perms=0o444):
+                 owner='root', group='root', perms=0o444,
+                 on_change_action=None):
         self.source = source
         self.target = target
         self.owner = owner
         self.group = group
         self.perms = perms
+        self.on_change_action = on_change_action
 
     def __call__(self, manager, service_name, event_name):
+        pre_checksum = ''
+        if self.on_change_action and os.path.isfile(self.target):
+            pre_checksum = host.file_hash(self.target)
         service = manager.get_service(service_name)
         context = {}
         for ctx in service.get('required_data', []):
             context.update(ctx)
         templating.render(self.source, self.target, context,
                           self.owner, self.group, self.perms)
+        if self.on_change_action:
+            if pre_checksum == host.file_hash(self.target):
+                hookenv.log(
+                    'No change detected: {}'.format(self.target),
+                    hookenv.DEBUG)
+            else:
+                self.on_change_action()
 
 
 # Convenience aliases for templates