diff --git a/overviewer.py b/overviewer.py
index 71bdb14..b33acfa 100755
--- a/overviewer.py
+++ b/overviewer.py
@@ -66,6 +66,7 @@ def main():
     parser.add_option("-p", "--processes", dest="procs", action="store", type="int",
             help="The number of local worker processes to spawn. Defaults to the number of CPU cores your computer has")
 
+    parser.add_option("--pid", dest="pid", action="store", help="Specify the pid file to use.")
     # Options that only apply to the config-less render usage
     parser.add_option("--rendermodes", dest="rendermodes", action="store",
             help="If you're not using a config file, specify which rendermodes to render with this option. This is a comma-separated list.")
@@ -138,6 +139,18 @@ def main():
             print("(build info not found)")
         return 0
 
+    if options.pid:
+        if os.path.exists(options.pid):
+            try:
+                with open(options.pid, 'r') as fpid:
+                    pid = int(fpid.read())
+                    if util.pid_exists(pid):
+                        print("Already running (pid exists) - exiting..")
+                        return 0
+            except IOError, ValueError:
+                pass
+        with open(options.pid,"w") as f:
+            f.write(str(os.getpid()))
     # if --check-terrain was specified, but we have NO config file, then we cannot
     # operate on a custom texture path.  we do terrain checking with a custom texture
     # pack later on, after we've parsed the config file
@@ -493,6 +506,8 @@ dir but you forgot to put quotes around the directory, since it contains spaces.
         logging.debug("Final cache stats:")
         for c in caches:
             logging.debug("\t%s: %s hits, %s misses", c.__class__.__name__, c.hits, c.misses)
+    if options.pid:
+        os.remove(options.pid)
 
     return 0
 
diff --git a/overviewer_core/util.py b/overviewer_core/util.py
index d936cba..6b81d8b 100644
--- a/overviewer_core/util.py
+++ b/overviewer_core/util.py
@@ -24,7 +24,7 @@ import platform
 from string import hexdigits
 from subprocess import Popen, PIPE
 from itertools import cycle, islice, product
-
+import errno
 def get_program_path():
     if hasattr(sys, "frozen") or imp.is_frozen("__main__"):
         return os.path.dirname(sys.executable)
@@ -391,3 +391,14 @@ try:
     OrderedDict = collections.OrderedDict
 except (ImportError, AttributeError):
     pass
+
+def pid_exists(pid): # http://stackoverflow.com/a/6940314/1318435
+    """Check whether pid exists in the current process table."""
+    if pid < 0:
+        return False
+    try:
+        os.kill(pid, 0)
+    except OSError, e:
+        return e.errno != errno.ESRCH
+    else:
+        return True
\ No newline at end of file