add a zombie example

To show that processes become zombies if you don't wait.
Also show that init becomes the father of your zombies if the original father
dies.

Signed-off-by: Manuel Traut <manut@linutronix.de>

3 files changed, 51 insertions, 0 deletions

diff --git a/schulung_tools/zombie/Makefile b/schulung_tools/zombie/Makefile
new file mode 100644
index 0000000..58c8196
--- /dev/null
+++ b/schulung_tools/zombie/Makefile
@@ -0,0 +1,8 @@
+CFLAGS += -g
+
+zombie: zombie.c
+
+clean:
+	rm -f zombie
+
+.PHONY: clean
diff --git a/schulung_tools/zombie/README b/schulung_tools/zombie/README
new file mode 100644
index 0000000..8c8561a
--- /dev/null
+++ b/schulung_tools/zombie/README
@@ -0,0 +1,2 @@
+This program demonstrates that children processes will become zombies if
+they exit but the parent does not clean them up.
diff --git a/schulung_tools/zombie/zombie.c b/schulung_tools/zombie/zombie.c
new file mode 100644
index 0000000..cc5e145
--- /dev/null
+++ b/schulung_tools/zombie/zombie.c
@@ -0,0 +1,41 @@
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+
+int main(void)
+{
+	pid_t pid;
+	int i;
+
+	for (i = 0; i < 10; i++) {
+		pid = fork();
+		if (pid == -1) {
+			printf("fork() failed\n");
+			return 0;
+		} else if (pid == 0) {
+			printf("child: pid=%d\n", getpid());
+			sleep(10);
+			printf("child: exiting pid=%d\n", getpid());
+			return 0;
+		} else {
+			printf("parent: created child %d\n", pid);
+		}
+	}
+
+/* if we don't clean up the children, they are zombies */
+#if 0
+	while (wait(&i) != -1)
+		/* NOP */;
+#endif
+
+/* if we don't clean up the children and the main process terminates
+ * init becomes parent of the childs
+ */
+#if 0
+	while (1)
+		sleep(100);
+#endif
+
+	return 0;
+}