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// Copyright (c) 2003-2011 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//
#include "common/exception.h"
#include "daemonizer/posix_fork.h"
#include "misc_log_ex.h"
#include <cstdlib>
#include <fcntl.h>
#include <unistd.h>
#include <stdexcept>
#include <string>
#include <sys/stat.h>
namespace posix {
namespace {
void quit(std::string const & message)
{
LOG_ERROR(message);
throw tools::runtime_error(message);
}
}
void 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.
exit(0);
}
else
{
quit("First fork failed");
}
}
// 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.
if (chdir("/") < 0)
{
quit("Unable to change working directory to root");
}
// 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
{
quit("Second fork failed");
}
}
// 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)
{
quit("Unable to open /dev/null");
}
// Send standard output to a log file.
const char* output = "/tmp/bitmonero.daemon.stdout.stderr";
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)
{
quit("Unable to open output file: " + std::string(output));
}
// Also send standard error to the same log file.
if (dup(1) < 0)
{
quit("Unable to dup output descriptor");
}
}
} // namespace posix
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