diff --git a/userland/bin/sh/sh.c b/userland/bin/sh/sh.c
index 2b9819f..565665e 100644
--- a/userland/bin/sh/sh.c
+++ b/userland/bin/sh/sh.c
@@ -534,7 +534,7 @@ interactive(void)
 	struct exitinfo ei;
 
 	while (1) {
-		printf("OS/161$ ");
+		printsf("OS/161$ ");
 		getcmd(buf, sizeof(buf));
 		docommand(buf, &ei);
 		printstatus(&ei, 0);
diff --git a/userland/include/stdio.h b/userland/include/stdio.h
index 20e96cb..440a822 100644
--- a/userland/include/stdio.h
+++ b/userland/include/stdio.h
@@ -56,6 +56,11 @@ int vprintf(const char *fmt, __va_list ap);
 int snprintf(char *buf, size_t len, const char *fmt, ...);
 int vsnprintf(char *buf, size_t len, const char *fmt, __va_list ap);
 
+/* Automated testing extensions. */
+
+int tprintf(const char *fmt, ...);
+int printsf(const char *fmt, ...);
+
 /* Print the argument string and then a newline. Returns 0 or -1 on error. */
 int puts(const char *);
 
diff --git a/userland/lib/libc/stdio/printf.c b/userland/lib/libc/stdio/printf.c
index f0d627b..51553b0 100644
--- a/userland/lib/libc/stdio/printf.c
+++ b/userland/lib/libc/stdio/printf.c
@@ -31,6 +31,8 @@
 #include <stdarg.h>
 #include <unistd.h>
 #include <errno.h>
+#include <string.h>
+#include <kern/secret.h>
 
 /*
  * printf - C standard I/O function.
@@ -76,3 +78,36 @@ vprintf(const char *fmt, va_list ap)
 	}
 	return chars;
 }
+
+/* printf variant that is quiet during automated testing */
+int
+tprintf(const char *fmt, ...)
+{
+	int chars;
+	va_list ap;
+	
+	if (strcmp(KERNEL_SECRET, "") != 0) {
+		return 0;
+	}
+	
+	va_start(ap, fmt);
+	chars = vprintf(fmt, ap);
+	va_end(ap);
+
+	return chars;
+}
+
+/* printf variant that prepends the kernel secret */
+int
+printsf(const char *fmt, ...)
+{
+	int chars;
+	va_list ap;
+	
+	printf("%s: ", KERNEL_SECRET);	
+	va_start(ap, fmt);
+	chars = vprintf(fmt, ap);
+	va_end(ap);
+
+	return chars;
+}
diff --git a/userland/testbin/randcall/gencalls.sh b/userland/testbin/randcall/gencalls.sh
index 2276e7a..f708da1 100755
--- a/userland/testbin/randcall/gencalls.sh
+++ b/userland/testbin/randcall/gencalls.sh
@@ -67,7 +67,7 @@ awk < $1 '
 	    if (i<NF) printf ", ";
 	}
 	printf ");\n";
-	printf"\tprintf(\"%%-47s\", buf);\n";
+	printf"\ttprintf(\"%%-47s\", buf);\n";
 	#printf "\tfflush(stdout);\n";
 	printf "\n";
 
@@ -88,7 +88,7 @@ awk < $1 '
 	}
 	printf ");\n";
 
-	printf "\tprintf(\" result %%d, errno %%d\\n\", result, errno);\n";
+	printf "\ttprintf(\" result %%d, errno %%d\\n\", result, errno);\n";
 	printf "\tif (dofork) {\n";
 	printf "\t\texit(0);\n";
 	printf "\t}\n";
diff --git a/userland/testbin/randcall/main.c b/userland/testbin/randcall/main.c
index 1b87a73..1b899ef 100644
--- a/userland/testbin/randcall/main.c
+++ b/userland/testbin/randcall/main.c
@@ -157,7 +157,7 @@ main(int argc, char *argv[])
 		}
 	}
 
-	printf("Seed: %d  Count: %d\n", seed, count);
+	tprintf("Seed: %d  Count: %d\n", seed, count);
 
 	srandom(seed);
 	trycalls(an, dofork, count);