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109 lines
2.7 KiB
C++
109 lines
2.7 KiB
C++
// Copyright (c) 2003-2011 Christopher M. Kohlhoff (chris at kohlhoff dot com)
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//
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// Distributed under the Boost Software License, Version 1.0. (See accompanying
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// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
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//
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#include "daemonizer/posix_fork.h"
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#include "misc_log_ex.h"
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#include <cstdlib>
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#include <fcntl.h>
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#include <unistd.h>
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#include <stdexcept>
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#include <string>
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#include <sys/stat.h>
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namespace posix {
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namespace {
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void quit(std::string const & message)
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{
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LOG_ERROR(message);
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throw std::runtime_error(message);
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}
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}
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void fork()
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{
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// Fork the process and have the parent exit. If the process was started
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// from a shell, this returns control to the user. Forking a new process is
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// also a prerequisite for the subsequent call to setsid().
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if (pid_t pid = ::fork())
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{
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if (pid > 0)
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{
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// We're in the parent process and need to exit.
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//
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// When the exit() function is used, the program terminates without
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// invoking local variables' destructors. Only global variables are
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// destroyed.
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exit(0);
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}
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else
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{
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quit("First fork failed");
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}
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}
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// Make the process a new session leader. This detaches it from the
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// terminal.
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setsid();
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// A process inherits its working directory from its parent. This could be
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// on a mounted filesystem, which means that the running daemon would
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// prevent this filesystem from being unmounted. Changing to the root
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// directory avoids this problem.
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if (chdir("/") < 0)
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{
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quit("Unable to change working directory to root");
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}
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// The file mode creation mask is also inherited from the parent process.
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// We don't want to restrict the permissions on files created by the
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// daemon, so the mask is cleared.
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umask(0);
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// A second fork ensures the process cannot acquire a controlling terminal.
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if (pid_t pid = ::fork())
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{
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if (pid > 0)
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{
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exit(0);
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}
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else
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{
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quit("Second fork failed");
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}
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}
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// Close the standard streams. This decouples the daemon from the terminal
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// that started it.
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close(0);
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close(1);
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close(2);
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// We don't want the daemon to have any standard input.
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if (open("/dev/null", O_RDONLY) < 0)
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{
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quit("Unable to open /dev/null");
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}
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// Send standard output to a log file.
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const char* output = "/tmp/bitmonero.daemon.stdout.stderr";
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const int flags = O_WRONLY | O_CREAT | O_APPEND;
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const mode_t mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
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if (open(output, flags, mode) < 0)
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{
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quit("Unable to open output file: " + std::string(output));
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}
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// Also send standard error to the same log file.
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if (dup(1) < 0)
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{
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quit("Unable to dup output descriptor");
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}
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}
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} // namespace posix
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