From 67408cf8fb6cfc648bd1e622ef497b068e078ef1 Mon Sep 17 00:00:00 2001
From: Val Packett <val@invisiblethingslab.com>
Date: Fri, 3 Oct 2025 04:13:26 -0300
Subject: [PATCH] init: allow running the user-provided init as pid 1 (fix
 #223)

Some init systems like systemd absolutely need to run as PID 1.
Add an environment variable to allow doing so at the cost of the return
code feature.

Signed-off-by: Val Packett <val@invisiblethingslab.com>
---
 init/init.c | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/init/init.c b/init/init.c
index 309f41c64..5ab2c7ee7 100644
--- a/init/init.c
+++ b/init/init.c
@@ -2,6 +2,7 @@
 #include <errno.h>
 #include <fcntl.h>
 #include <limits.h>
+#include <stdbool.h>
 #include <stdint.h>
 #include <stdio.h>
 #include <stdlib.h>
@@ -1044,6 +1045,7 @@ int main(int argc, char **argv)
     int sockfd;
     int status;
     int saved_errno;
+    bool init_pid1 = false;
     char localhost[] = "localhost\0";
     char *hostname;
     char *krun_home;
@@ -1052,6 +1054,7 @@ int main(int argc, char **argv)
     char *krun_root;
     char *krun_root_fstype;
     char *krun_root_options;
+    char *env_init_pid1;
     char *config_workdir, *env_workdir;
     char *rlimits;
     char **config_argv, **exec_argv;
@@ -1186,12 +1189,21 @@ int main(int argc, char **argv)
         exec_argv[0] = &DEFAULT_KRUN_INIT[0];
     }
 
+    env_init_pid1 = getenv("KRUN_INIT_PID1");
+    if (env_init_pid1 && *env_init_pid1 == '1') {
+        init_pid1 = true;
+    }
+
 #ifdef __TIMESYNC__
     if (fork() == 0) {
         clock_worker();
     }
 #endif
 
+    if (init_pid1) {
+        goto exec_init;
+    }
+
     // We need to fork ourselves, because pid 1 cannot doesn't receive SIGINT
     // signal
     int child = fork();
@@ -1201,6 +1213,7 @@ int main(int argc, char **argv)
         exit(125);
     }
     if (child == 0) { // child
+    exec_init:
         if (setup_redirects() < 0) {
             exit(125);
         }