# Node ID 06c8c441324ae4ac3278337b156507a1a919c8a2
# Parent  98ff815cc629b071cc76d161ae2fc780ad847407
diff --git a/src/python/m5/main.py b/src/python/m5/main.py
--- a/src/python/m5/main.py
+++ b/src/python/m5/main.py
@@ -194,6 +194,13 @@
     event.mainq = event.getEventQueue(0)
     event.setEventQueue(event.mainq)
 
+    # If outdir has any '$$' patterns in it, replace them with the
+    # process ID.  This allows users to easily make unique output dirs.
+    # To enable this by default, add a line like the following to your
+    # ~/.m5/options.py file:
+    #    options.set_defaults(outdir="m5out/pid$$")
+    options.outdir = options.outdir.replace('$$', str(os.getpid()))
+
     if not os.path.isdir(options.outdir):
         os.makedirs(options.outdir)