diff --git a/lib/backend.py b/lib/backend.py
index 58c789ab6e62ff21f5e95e6f9bb2e8140c38b239..515306be9d22e9921d8b395e1772fe194b685d49 100644
--- a/lib/backend.py
+++ b/lib/backend.py
@@ -1930,11 +1930,13 @@ def OSFromDisk(name, base_dir=None):
   return payload
 
 
-def OSCoreEnv(inst_os, debug=0):
+def OSCoreEnv(inst_os, os_params, debug=0):
   """Calculate the basic environment for an os script.
 
   @type inst_os: L{objects.OS}
   @param inst_os: operating system for which the environment is being built
+  @type os_params: dict
+  @param os_params: the OS parameters
   @type debug: integer
   @param debug: debug level (0 or 1, for OS Api 10)
   @rtype: dict
@@ -1958,6 +1960,10 @@ def OSCoreEnv(inst_os, debug=0):
       variant = inst_os.supported_variants[0]
     result['OS_VARIANT'] = variant
 
+  # OS params
+  for pname, pvalue in os_params.items():
+    result['OSP_%s' % pname.upper()] = pvalue
+
   return result
 
 
@@ -1976,7 +1982,7 @@ def OSEnvironment(instance, inst_os, debug=0):
       cannot be found
 
   """
-  result = OSCoreEnv(inst_os, debug)
+  result = OSCoreEnv(inst_os, instance.osparams, debug=debug)
 
   result['INSTANCE_NAME'] = instance.name
   result['INSTANCE_OS'] = instance.os
diff --git a/lib/objects.py b/lib/objects.py
index 1e2d1bbfe0cfb8788cd79ce3beea0693ea8cfe6e..4f9314fc2389a6f30e0b158f35c3aa8b7421bf51 100644
--- a/lib/objects.py
+++ b/lib/objects.py
@@ -657,6 +657,7 @@ class Instance(TaggableObject):
     "hypervisor",
     "hvparams",
     "beparams",
+    "osparams",
     "admin_up",
     "nics",
     "disks",
@@ -812,6 +813,8 @@ class Instance(TaggableObject):
           del self.hvparams[key]
         except KeyError:
           pass
+    if self.osparams is None:
+      self.osparams = {}
 
 
 class OS(ConfigObject):
@@ -869,6 +872,7 @@ class Cluster(TaggableObject):
     "hvparams",
     "os_hvp",
     "beparams",
+    "osparams",
     "nicparams",
     "candidate_pool_size",
     "modify_etc_hosts",
@@ -893,6 +897,10 @@ class Cluster(TaggableObject):
     if self.os_hvp is None:
       self.os_hvp = {}
 
+    # osparams added before 2.2
+    if self.osparams is None:
+      self.osparams = {}
+
     self.beparams = UpgradeGroupedParams(self.beparams,
                                          constants.BEC_DEFAULTS)
     migrate_default_bridge = not self.nicparams
@@ -1043,6 +1051,26 @@ class Cluster(TaggableObject):
     """
     return FillDict(self.nicparams.get(constants.PP_DEFAULT, {}), nicparams)
 
+  def SimpleFillOS(self, os_name, os_params):
+    """Fill an instance's osparams dict with cluster defaults.
+
+    @type os_name: string
+    @param os_name: the OS name to use
+    @type os_params: dict
+    @param os_params: the dict to fill with default values
+    @rtype: dict
+    @return: a copy of the instance's osparams with missing keys filled from
+        the cluster defaults
+
+    """
+    name_only = os_name.split("+", 1)[0]
+    # base OS
+    result = self.osparams.get(name_only, {})
+    # OS with variant
+    result = FillDict(result, self.osparams.get(os_name, {}))
+    # specified params
+    return FillDict(result, os_params)
+
 
 class BlockDevStatus(ConfigObject):
   """Config object representing the status of a block device."""
diff --git a/lib/rpc.py b/lib/rpc.py
index 6b3aa9f7ceb880ffbe6dccd0d51e626aa9f3fe3f..57dd960e4f1a2ecb6ad17e95d297435111712fa9 100644
--- a/lib/rpc.py
+++ b/lib/rpc.py
@@ -329,7 +329,7 @@ class RpcRunner(object):
     self._cfg = cfg
     self.port = utils.GetDaemonPort(constants.NODED)
 
-  def _InstDict(self, instance, hvp=None, bep=None):
+  def _InstDict(self, instance, hvp=None, bep=None, osp=None):
     """Convert the given instance to a dict.
 
     This is done via the instance's ToDict() method and additionally
@@ -341,6 +341,8 @@ class RpcRunner(object):
     @param hvp: a dictionary with overridden hypervisor parameters
     @type bep: dict or None
     @param bep: a dictionary with overridden backend parameters
+    @type osp: dict or None
+    @param osp: a dictionary with overriden os parameters
     @rtype: dict
     @return: the instance dict, with the hvparams filled with the
         cluster defaults
@@ -354,6 +356,9 @@ class RpcRunner(object):
     idict["beparams"] = cluster.FillBE(instance)
     if bep is not None:
       idict["beparams"].update(bep)
+    idict["osparams"] = cluster.SimpleFillOS(instance.os, instance.osparams)
+    if osp is not None:
+      idict["osparams"].update(osp)
     for nic in idict["nics"]:
       nic['nicparams'] = objects.FillDict(
         cluster.nicparams[constants.PP_DEFAULT],