diff --git a/bin/logtool b/bin/logtool
index e9216965148498d933443caf9e81df1f24a7a965..5c8cd372171ae1124735bc9e9a17a3f71bf336be 100755
--- a/bin/logtool
+++ b/bin/logtool
@@ -150,7 +150,7 @@ following:
             # not a known command, interpret as file name
             from os import access, R_OK
             if access(cmd, R_OK):
-                logmgr = LogManager(cmd)
+                logmgr = LogManager(cmd, "r")
             else:
                 raise IOError, "file '%s' not found" % cmd
 
diff --git a/src/batchjob.py b/src/batchjob.py
index 585f5d6a023b2b8cf373741415d9e539ea51c83f..2b568a9e0e5583da42954eecfa1adaf7e6317d04 100644
--- a/src/batchjob.py
+++ b/src/batchjob.py
@@ -14,13 +14,21 @@ def _cp(src, dest):
 
 
 
+def get_timestamp():
+    from datetime import datetime
+    return datetime.now().strftime("%Y-%m-%d-%H%M%S")
+
+
+
+
 class BatchJob(object):
-    def __init__(self, moniker, main_file, aux_files=[]):
-        from datetime import datetime
+    def __init__(self, moniker, main_file, aux_files=[], timestamp=None):
         import os
         import os.path
 
-        timestamp = datetime.now().strftime("%Y-%m-%d-%H%M")
+        if timestamp is None:
+            timestamp = get_timestamp()
+
         self.moniker = (
                 moniker
                 .replace("-$DATE", "")
@@ -30,6 +38,7 @@ class BatchJob(object):
         self.subdir = os.path.join(
                 os.getcwd(),
                 moniker.replace("$DATE", timestamp))
+
         os.makedirs(self.subdir)
 
         with open("%s/run.sh" % self.subdir, "w") as runscript:
diff --git a/src/log.py b/src/log.py
index 23182b0d2dac0fbc0354e6174282c30bc50af187..37449710bdd119229b498fd44b1067700888f69a 100644
--- a/src/log.py
+++ b/src/log.py
@@ -159,14 +159,21 @@ class LogManager(object):
     data in a saved log.
     """
 
-    def __init__(self, filename, mpi_comm=None):
+    def __init__(self, filename, mode, mpi_comm=None):
         """Initialize this log manager instance.
 
         @arg filename: If given, the filename to which this log is bound.
           If this database exists, the current state is loaded from it.
+        @arg mode: One of "w", "r" for write, read. "w" assumes that the 
+          database is initially empty.
         @arg mpi_comm: A C{boost.mpi} communicator. If given, logs are periodically
           synchronized to the head node, which then writes them out to disk.
         """
+
+        assert isinstance(mode, basestring), "mode must be a string"
+        mode = mode[0]
+        assert mode in ["w", "r"], "invalid mode"
+
         self.quantity_data = {}
         self.quantity_table = {}
         self.gather_descriptors = []
@@ -202,8 +209,13 @@ class LogManager(object):
             self.db_conn = sqlite3.connect(filename, timeout=30)
             try:
                 self.db_conn.execute("select * from quantities;")
+                if mode == "w":
+                    raise RuntimeError, "Log database '%s' already exists" % filename
                 self._load()
             except sqlite3.OperationalError:
+                if mode == "r":
+                    raise RuntimeError, "Log database '%s' not found" % filename
+
                 # initialize new database
                 self.db_conn.execute("""
                   create table quantities (