--- a/linux_ulog.h
+++ b/linux_ulog.h
@@ -8,6 +8,7 @@
 #include <pthread.h>
 #include <iostream>
 #include <sys/types.h>
+#include <unistd.h> /* getpid() */
 #include <sys/socket.h>
 
 /// linux specific headers!