bootloader: gracefully reboot using '/sbin/init 6'

This patch mainly aims to add a graceful reboot by executing
'/sbin/init 6' rather than calling reboot system call.

Signed-off-by: Ming Liu <liu.ming50@gmail.com>

src/libaktualizr/bootloader/bootloader.cc

@@ -1,8 +1,9 @@
 #include <fcntl.h>
 #include <sys/stat.h>
-
+#include <sys/types.h>
 #include <sys/reboot.h>
 #include <unistd.h>
+#include <stdlib.h>
 
 #include <boost/filesystem.hpp>
 
@@ -169,13 +170,20 @@ void Bootloader::rebootFlagClear() {
 }
 
 void Bootloader::reboot(bool fake_reboot) {
+  struct stat st;
+
   if (fake_reboot) {
     boost::filesystem::remove(reboot_sentinel_);
   } else {
-    sync();
     if (setuid(0) != 0) {
       LOG_ERROR << "Failed to set/verify a root user so cannot reboot system programmatically";
+      return;
+    }
+
+    if ((stat ("/sbin/init", &st) >= 0) && (st.st_mode & (S_IXUSR | S_IXGRP | S_IXOTH))) {
+      system("/sbin/init 6");
     } else {
+      sync();
       ::reboot(RB_AUTOBOOT);
     }
   }