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145 lines
3.4 KiB
145 lines
3.4 KiB
// 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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#ifndef TMPDIR
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#define TMPDIR "/tmp"
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#endif
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namespace posix {
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namespace {
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void quit(const std::string & 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(const std::string & pidfile)
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{
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// If a PID file is specified, we open the file here, because
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// we can't report errors after the fork operation.
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// When we fork, we close thise file in each of the parent
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// processes.
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// Only in the final child process do we write the PID to the
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// file (and close it).
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std::ofstream pidofs;
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if (! pidfile.empty ())
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{
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int oldpid;
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std::ifstream pidrifs;
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pidrifs.open(pidfile, std::fstream::in);
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if (! pidrifs.fail())
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{
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// Read the PID and send signal 0 to see if the process exists.
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if (pidrifs >> oldpid && oldpid > 1 && kill(oldpid, 0) == 0)
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{
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quit("PID file " + pidfile + " already exists and the PID therein is valid");
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}
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pidrifs.close();
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}
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pidofs.open(pidfile, std::fstream::out | std::fstream::trunc);
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if (pidofs.fail())
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{
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quit("Failed to open specified PID file for writing");
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}
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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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pidofs.close();
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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 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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pidofs.close();
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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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if (! pidofs.fail())
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{
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int pid = ::getpid();
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pidofs << pid << std::endl;
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pidofs.close();
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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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#ifdef DEBUG_TMPDIR_LOG
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// Send standard output to a log file.
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const char *tmpdir = getenv("TMPDIR");
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if (!tmpdir)
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tmpdir = TMPDIR;
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std::string output = tmpdir;
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output += "/wownero.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.c_str(), flags, mode) < 0)
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{
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quit("Unable to open output file: " + output);
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}
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#else
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if (open("/dev/null", O_WRONLY) < 0)
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{
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quit("Unable to open /dev/null");
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}
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#endif
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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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