Allow daemon to fork on posix systems

src/CMakeLists.txt

@@ -4,7 +4,10 @@ file(GLOB_RECURSE COMMON common/*)
 file(GLOB_RECURSE CRYPTO crypto/*)
 file(GLOB_RECURSE CRYPTONOTE_CORE cryptonote_core/*)
 file(GLOB_RECURSE CRYPTONOTE_PROTOCOL cryptonote_protocol/*)
-file(GLOB_RECURSE DAEMON daemon/*)
+file(GLOB_RECURSE DAEMON daemon/*.cpp)
+if(WIN32)
+  list(REMOVE_ITEM DAEMON "daemon/posix_fork.cpp")
+endif()
 file(GLOB_RECURSE P2P p2p/*)
 file(GLOB_RECURSE RPC rpc/*)
 file(GLOB_RECURSE SIMPLEWALLET simplewallet/*)

src/daemon/daemon.cpp

@@ -23,9 +23,9 @@ using namespace epee;
 #include "rpc/core_rpc_server.h"
 #include "cryptonote_protocol/cryptonote_protocol_handler.h"
 
-//#ifndef WIN32
-//#include "posix_daemonize.h"
-//#endif
+#ifndef WIN32
+#include "posix_fork.h"
+#endif
 
 #ifdef WIN32
 #include <crtdbg.h>
@@ -166,8 +166,8 @@ int main(int argc, char* argv[])
 
 #ifndef WIN32
   if (command_line::arg_present(vm, arg_detach)) {
-    std::cout << "start daemon" << std::endl;
-    return 0;
+    std::cout << "forking to background..." << std::endl;
+    posix_fork();
   }
 #endif
 
@@ -225,9 +225,10 @@ int main(int argc, char* argv[])
   CHECK_AND_ASSERT_MES(res, 1, "Failed to initialize core");
   LOG_PRINT_L0("Core initialized OK");
 
-  // start components
-  if(!command_line::has_arg(vm, arg_console))
+  // Start handling console input if requested and not detached
+  if(!command_line::arg_present(vm, arg_console) && !command_line::arg_present(vm, arg_detach))
   {
+    LOG_PRINT_L0("Begin handling console input");
     console_command_thread.start();
   }
 

src/daemon/posix_fork.cpp

@@ -0,0 +1,104 @@
+#include "daemon/posix_fork.h"
+
+#include <cstdlib>
+#include <syslog.h>
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/stat.h>
+
+namespace daemonize {
+
+void posix_fork()
+{
+  // Fork the process and have the parent exit. If the process was started
+  // from a shell, this returns control to the user. Forking a new process is
+  // also a prerequisite for the subsequent call to setsid().
+  if (pid_t pid = fork())
+  {
+    if (pid > 0)
+    {
+      // We're in the parent process and need to exit.
+      //
+      // When the exit() function is used, the program terminates without
+      // invoking local variables' destructors. Only global variables are
+      // destroyed. As the io_service object is a local variable, this means
+      // we do not have to call:
+      //
+      //   io_service.notify_fork(boost::asio::io_service::fork_parent);
+      //
+      // However, this line should be added before each call to exit() if
+      // using a global io_service object. An additional call:
+      //
+      //   io_service.notify_fork(boost::asio::io_service::fork_prepare);
+      //
+      // should also precede the second fork().
+      exit(0);
+    }
+    else
+    {
+      syslog(LOG_ERR | LOG_USER, "First fork failed: %m");
+      exit(1);
+    }
+  }
+
+  // Make the process a new session leader. This detaches it from the
+  // terminal.
+  setsid();
+
+  // A process inherits its working directory from its parent. This could be
+  // on a mounted filesystem, which means that the running daemon would
+  // prevent this filesystem from being unmounted. Changing to the root
+  // directory avoids this problem.
+  chdir("/");
+
+  // The file mode creation mask is also inherited from the parent process.
+  // We don't want to restrict the permissions on files created by the
+  // daemon, so the mask is cleared.
+  umask(0);
+
+  // A second fork ensures the process cannot acquire a controlling terminal.
+  if (pid_t pid = fork())
+  {
+    if (pid > 0)
+    {
+      exit(0);
+    }
+    else
+    {
+      syslog(LOG_ERR | LOG_USER, "Second fork failed: %m");
+      exit(1);
+    }
+  }
+
+  // Close the standard streams. This decouples the daemon from the terminal
+  // that started it.
+  close(0);
+  close(1);
+  close(2);
+
+  // We don't want the daemon to have any standard input.
+  if (open("/dev/null", O_RDONLY) < 0)
+  {
+    syslog(LOG_ERR | LOG_USER, "Unable to open /dev/null: %m");
+    exit(1);
+  }
+
+  // Send standard output to a log file.
+  const char* output = "/tmp/bitmonero.daemon.out";
+  const int flags = O_WRONLY | O_CREAT | O_APPEND;
+  const mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
+  if (open(output, flags, mode) < 0)
+  {
+    syslog(LOG_ERR | LOG_USER, "Unable to open output file %s: %m", output);
+    exit(1);
+  }
+
+  // Also send standard error to the same log file.
+  if (dup(1) < 0)
+  {
+    syslog(LOG_ERR | LOG_USER, "Unable to dup output descriptor: %m");
+    exit(1);
+  }
+}
+
+}

src/daemon/posix_fork.h

@@ -0,0 +1,7 @@
+#pragma once
+
+namespace daemonize {
+
+void posix_fork();
+
+} // namespace daemonize