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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 "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>
#ifndef TMPDIR
#define TMPDIR "/tmp"
#endif
namespace posix {
namespace {
void quit(const std::string & message)
{
LOG_ERROR(message);
throw std::runtime_error(message);
}
}
void fork(const std::string & pidfile)
{
// If a PID file is specified, we open the file here, because
// we can't report errors after the fork operation.
// When we fork, we close thise file in each of the parent
// processes.
// Only in the final child process do we write the PID to the
// file (and close it).
std::ofstream pidofs;
if (! pidfile.empty ())
{
int oldpid;
std::ifstream pidrifs;
pidrifs.open(pidfile, std::fstream::in);
if (! pidrifs.fail())
{
// Read the PID and send signal 0 to see if the process exists.
if (pidrifs >> oldpid && oldpid > 1 && kill(oldpid, 0) == 0)
{
quit("PID file " + pidfile + " already exists and the PID therein is valid");
}
pidrifs.close();
}
pidofs.open(pidfile, std::fstream::out | std::fstream::trunc);
if (pidofs.fail())
{
quit("Failed to open specified PID file for writing");
}
}
// 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.
pidofs.close();
// 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 second fork ensures the process cannot acquire a controlling terminal.
if (pid_t pid = ::fork())
{
if (pid > 0)
{
pidofs.close();
exit(0);
}
else
{
quit("Second fork failed");
}
}
if (! pidofs.fail())
{
int pid = ::getpid();
pidofs << pid << std::endl;
pidofs.close();
}
// 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 *tmpdir = getenv("TMPDIR");
if (!tmpdir)
tmpdir = TMPDIR;
std::string output = tmpdir;
output += "/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.c_str(), flags, mode) < 0)
{
quit("Unable to open output file: " + 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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