Properly detach from background process.

src/rpc/exec_file.cc

@@ -79,6 +79,23 @@ ExecFile::execute(const char* file, char* const* argv, int flags) {
     throw torrent::input_error("ExecFile::execute(...) Fork failed.");
 
   if (childPid == 0) {
+    if (flags & flag_background) {
+      pid_t detached_pid = fork();
+
+      if (detached_pid == -1)
+        _exit(-1);
+
+      if (detached_pid != 0) {
+        if (m_logFd != -1)
+          write(m_logFd, "\n--- Background task ---\n", sizeof("\n--- Background task ---\n"));
+
+        _exit(0);
+      }
+
+      m_logFd = -1;
+      flags &= ~flag_capture;
+    }
+
     int devNull = open("/dev/null", O_RDWR);
     if (devNull != -1)
       dup2(devNull, 0);
@@ -110,13 +127,6 @@ ExecFile::execute(const char* file, char* const* argv, int flags) {
     _exit(result);
   }
 
-  if (flags & flag_background) {
-    if (m_logFd != -1)
-      write(m_logFd, "\n--- Background task ---\n", sizeof("\n--- Background task ---\n"));
-
-    return 0;
-  }
-
   // We yield the global lock when waiting for the executed command to
   // finish so that XMLRPC and other threads can continue working.
   ThreadBase::release_global_lock();