diff --git a/lib/constants.py b/lib/constants.py
index 296ebde293d74e2ebf174cad09306cef461f54a7..f20117d13c22ab9c04e65cc27a577747a9c325aa 100644
--- a/lib/constants.py
+++ b/lib/constants.py
@@ -233,8 +233,14 @@ DEFAULT_VG = "xenvg"
 BIND_ADDRESS_GLOBAL = "0.0.0.0"
 MIN_VG_SIZE = 20480
 
-# valid os status
+# os related constants
 OS_VALID_STATUS = "VALID"
+OS_SCRIPT_CREATE = 'create'
+OS_SCRIPT_IMPORT = 'import'
+OS_SCRIPT_EXPORT = 'export'
+OS_SCRIPT_RENAME = 'rename'
+OS_SCRIPTS = frozenset([OS_SCRIPT_CREATE, OS_SCRIPT_IMPORT, 
+                        OS_SCRIPT_EXPORT, OS_SCRIPT_RENAME])
 
 # ssh constants
 SSH_INITD_SCRIPT = _autoconf.SSH_INITD_SCRIPT