diff --git a/kern/include/lib.h b/kern/include/lib.h
index b010a7b..a25c079 100644
--- a/kern/include/lib.h
+++ b/kern/include/lib.h
@@ -197,4 +197,13 @@ void kprintf_bootstrap(void);
 void random_yielder(uint32_t);
 void random_spinner(uint32_t);
 
+/*
+ * Testing variants of kprintf. tprintf is silent during automated testing.
+ * sprintf prefixes the kernel secret to kprintf messages during automated
+ * testing.
+ */
+
+int tkprintf(const char *format, ...) __PF(1,2);
+int skprintf(const char *format, ...) __PF(1,2);
+
 #endif /* _LIB_H_ */
diff --git a/kern/lib/kprintf.c b/kern/lib/kprintf.c
index 3adc7a3..397355e 100644
--- a/kern/lib/kprintf.c
+++ b/kern/lib/kprintf.c
@@ -39,6 +39,7 @@
 #include <mainbus.h>
 #include <vfs.h>          // for vfs_sync()
 #include <lamebus/ltrace.h> // for ltrace_stop()
+#include <kern/secret.h>
 
 
 /* Flags word for DEBUG() macro. */
@@ -90,13 +91,13 @@ console_send(void *junk, const char *data, size_t len)
 }
 
 /*
- * Printf to the console.
+ * kprintf and tprintf helper function.
  */
+inline
 int
-kprintf(const char *fmt, ...)
+vkprintf(const char *fmt, va_list ap)
 {
 	int chars;
-	va_list ap;
 	bool dolock;
 
 	dolock = kprintf_lock != NULL
@@ -111,9 +112,7 @@ kprintf(const char *fmt, ...)
 		spinlock_acquire(&kprintf_spinlock);
 	}
 
-	va_start(ap, fmt);
 	chars = __vprintf(console_send, NULL, fmt, ap);
-	va_end(ap);
 
 	if (dolock) {
 		lock_release(kprintf_lock);
@@ -125,6 +124,62 @@ kprintf(const char *fmt, ...)
 	return chars;
 }
 
+/*
+ * Printf to the console.
+ */
+int
+kprintf(const char *fmt, ...)
+{
+	int chars;
+	va_list ap;
+
+	va_start(ap, fmt);
+	chars = vkprintf(fmt, ap);
+	va_end(ap);
+
+	return chars;
+}
+
+/*
+ * kprintf variant that is quiet during automated testing
+ */
+int
+tkprintf(const char *fmt, ...)
+{
+	int chars;
+	va_list ap;
+	
+	if (KERNEL_SECRET != 0) {
+		return 0;
+	}
+	
+	va_start(ap, fmt);
+	chars = vkprintf(fmt, ap);
+	va_end(ap);
+
+	return chars;
+}
+
+/*
+ * kprintf variant that prints the automated secret
+ */
+int
+skprintf(const char *fmt, ...)
+{
+	int chars;
+	va_list ap;
+	
+	if (KERNEL_SECRET != 0) {
+		kprintf("SECRET=%llu ", KERNEL_SECRET);
+	}
+	
+	va_start(ap, fmt);
+	chars = vkprintf(fmt, ap);
+	va_end(ap);
+
+	return chars;
+}
+
 /*
  * panic() is for fatal errors. It prints the printf arguments it's
  * passed and then halts the system.