[PATCH a001 v1 6/7] Create a simple init program

[Ammar Faizi <ammarfaizi2@gnuweeb.org>]

Using "tail -f /dev/null" as the init program is wrong because it
doesn't handle the SIGCHLD signal, resulting many zombie processes like
these:

  Zs   08:30   0:00 [master] <defunct>
  Z    08:30   0:00 [qmgr] <defunct>
  Zs   08:30   0:00 [dovecot] <defunct>
  Z    08:30   0:00 [anvil] <defunct>
  Z    08:30   0:00 [log] <defunct>
  Z    08:30   0:00 [config] <defunct>
  Z    08:30   0:00 [tlsmgr] <defunct>
  Z    08:30   0:00 [stats] <defunct>
  Z    08:33   0:00 [imap-login] <defunct>
  Z    08:33   0:00 [imap] <defunct>
  Z    08:33   0:00 [imap-login] <defunct>
  Z    08:33   0:00 [imap] <defunct>
  Z    08:39   0:01 [imap-login] <defunct>
  Z    08:39   0:03 [imap] <defunct>
  Z    11:50   0:00 [pickup] <defunct>
  Zs   12:31   0:00 [dovecot] <defunct>
  Z    12:31   0:00 [anvil] <defunct>
  Z    12:31   0:00 [log] <defunct>
  Z    12:31   0:00 [config] <defunct>
  Z    12:31   0:00 [imap-login] <defunct>
  Z    12:31   0:00 [stats] <defunct>
  Z    12:31   0:00 [imap] <defunct>

Create a simple init program that ignores SIGCHLD so that the zombie
processes are gone.

Signed-off-by: Ammar Faizi <ammarfaizi2@gnuweeb.org>
---
 .gitignore |  1 +
 Dockerfile |  5 +++--
 init.c     | 15 +++++++++++++++
 install.sh |  1 +
 4 files changed, 20 insertions(+), 2 deletions(-)
 create mode 100644 init.c

diff --git a/.gitignore b/.gitignore
index 50cf6dedd170238f..bceb5ce4098add1a 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1 +1,2 @@
 /config
+/init
diff --git a/Dockerfile b/Dockerfile
index 7bc54e0afb43d8ce..3492aa0408b7b5a3 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -41,10 +41,11 @@ RUN apt update \
        postfix-policyd-spf-python dovecot-core dovecot-imapd \
        dovecot-lmtpd dovecot-mysql opendkim opendmarc
 
+COPY init /bin/gwinitd
 COPY mailserver /root/mailserver
 RUN --mount=type=secret,required=true,id=config /root/mailserver/setup.sh
-
+RUN chmod -v +x /bin/gwinitd
 
 COPY docker-entrypoint.sh /
 ENTRYPOINT [ "/docker-entrypoint.sh" ]
-CMD [ "tail", "-f", "/dev/null" ]
+CMD [ "/bin/gwinitd" ]
diff --git a/init.c b/init.c
new file mode 100644
index 0000000000000000..adc67275dd3414c0
--- /dev/null
+++ b/init.c
@@ -0,0 +1,15 @@
+#include <signal.h>
+#include <unistd.h>
+
+int main(void)
+{
+	struct sigaction a = { .sa_handler = SIG_IGN };
+
+	if (sigaction(SIGCHLD, &a, NULL) < 0)
+		return 1;
+
+	while (1)
+		sleep(1000000);
+
+	return 0;
+}
diff --git a/install.sh b/install.sh
index 652861d263a698dc..dea60516f2e27512 100755
--- a/install.sh
+++ b/install.sh
@@ -1,4 +1,5 @@
 #!/bin/bash
 
 set -e;
+gcc -Wall -Wextra -Os init.c -o init;
 DOCKER_BUILDKIT=1 docker build --secret id=config -t server-a001 .;
-- 
Ammar Faizi