daemon.cpp   [plain text]

/*
 * Copyright (c) 2000-2001 Apple Computer, Inc. All Rights Reserved.
 * 
 * The contents of this file constitute Original Code as defined in and are
 * subject to the Apple Public Source License Version 1.2 (the 'License').
 * You may not use this file except in compliance with the License. Please obtain
 * a copy of the License at http://www.apple.com/publicsource and read it before
 * using this file.
 * 
 * This Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESS
 * OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES, INCLUDING WITHOUT
 * LIMITATION, ANY WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR
 * PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT. Please see the License for the
 * specific language governing rights and limitations under the License.
 */


//
// demon - support code for writing UNIXoid demons
//
#include <Security/daemon.h>
#include <Security/logging.h>
#include <Security/debugging.h>
#include <sys/types.h>
#include <errno.h>
#include <unistd.h>
#include <fcntl.h>

namespace Security {
namespace Daemon {


//
// Daemonize this process, the UNIX way.
//
bool incarnate()
{
	// fork with slight resilience
	for (int forkTries = 1; forkTries <= 5; forkTries++) {
		switch (fork()) {
		case 0:			// child
			// we are the daemon process (Har! Har!)
			break;
		case -1:		// parent: fork failed
			switch (errno) {
			case EAGAIN:
			case ENOMEM:
				Syslog::warning("fork() short on resources (errno=%d); retrying", errno);
				sleep(forkTries);
				continue;
			default:
				Syslog::error("fork() failed (errno=%d)", errno);
				return false;
			}
		default:		// parent
			// @@@ we could close an assurance loop here, but we don't (yet?)
			exit(0);
		}
	}
	
	// fork succeeded; we are the child; parent is terminating

	// create new session (the magic set-me-apart system call)
	setsid();

	// redirect standard channels to /dev/null
	close(0);	// fail silently in case 0 is closed
	if (open("/dev/null", O_RDWR, 0) == 0) {	// /dev/null could be missing, I suppose...
		dup2(0, 1);
		dup2(0, 2);
	}
	
	// ready to roll
	return true;
}


//
// Re-execute myself.
// This is a pretty bad hack for libraries that are pretty broken and (essentially)
// don't work after a fork() unless you also exec().
//
// WARNING: Don't even THINK of doing this in a setuid-anything program.
//
bool executeSelf(char **argv)
{
	static const char reExecEnv[] = "_RE_EXECUTE";
	if (getenv(reExecEnv)) {		// was re-executed
		debug("daemon", "self-execution complete");
		unsetenv(reExecEnv);
		return true;
	} else {
		setenv(reExecEnv, "go", 1);
		debug("daemon", "self-executing (ouch!)");
		execv(argv[0], argv);
		perror("re-execution");
		Syslog::error("Re-execution attempt failed");
		return false;
	}
}


} // end namespace Daemon
} // end namespace Security