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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_language.h"
#include "misc_log_ex.h"
#include <cerrno>
#include <cstdlib>
#include <cstring>
#include <fcntl.h>
#include <fstream>
#include <unistd.h>
#include <stdexcept>
#include <string>
#include <sys/stat.h>
#include <sys/types.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).
int pid_fd = -1;
auto close_pid_fd = [&pid_fd]()
{
if (pid_fd >= 0)
{
close(pid_fd);
pid_fd = -1;
}
};
epee::misc_utils::auto_scope_leave_caller pid_fd_guard =
epee::misc_utils::create_scope_leave_handler(close_pid_fd);
if (! pidfile.empty ())
{
struct stat st;
if (lstat(pidfile.c_str(), &st) == 0)
{
if (S_ISLNK(st.st_mode))
{
quit("PID file path is a symlink, refusing: " + pidfile);
}
if (!S_ISREG(st.st_mode))
{
quit("PID file path exists and is not a regular file: " + pidfile);
}
int oldpid = 0;
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.
errno = 0;
if (pidrifs >> oldpid && oldpid > 1 && (kill(oldpid, 0) == 0 || errno == EPERM))
{
quit("PID file " + pidfile + " already exists and the PID therein is valid");
}
pidrifs.close();
}
if (unlink(pidfile.c_str()) != 0)
{
quit("Failed to remove stale PID file: " + pidfile + ": " + std::strerror(errno));
}
}
else if (errno != ENOENT)
{
quit("Failed to inspect PID file path: " + pidfile + ": " + std::strerror(errno));
}
#ifdef O_NOFOLLOW
const int flags = O_WRONLY | O_CREAT | O_EXCL | O_NOFOLLOW;
#else
const int flags = O_WRONLY | O_CREAT | O_EXCL;
#endif
pid_fd = open(pidfile.c_str(), flags, 0644);
if (pid_fd < 0)
{
quit("Failed to create PID file: " + pidfile + ": " + std::strerror(errno));
}
}
// 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.
close_pid_fd();
// 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)
{
close_pid_fd();
exit(0);
}
else
{
quit("Second fork failed");
}
}
if (pid_fd >= 0)
{
const std::string pid = std::to_string(::getpid()) + "\n";
const ssize_t written = write(pid_fd, pid.data(), pid.size());
if (written < 0)
{
quit("Failed to write PID file: " + pidfile + ": " + std::strerror(errno));
}
if (static_cast<size_t>(written) != pid.size())
{
quit("Failed to write complete PID file: " + pidfile);
}
}
// 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");
}
#ifdef DEBUG_TMPDIR_LOG
// 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);
}
#else
if (open("/dev/null", O_WRONLY) < 0)
{
quit("Unable to open /dev/null");
}
#endif
// 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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