daemonize.c

/*
UNIX daemonizer.  Daemonizes any non-interactive console program and watches over it.
Whenever a signal is sent to this process, it halts the daemonized process as well.

To compile:	cc -o daemonize daemonize.c
Usage:		./daemonize -?
Users of this:	catalina initscript
*/

#include <stdio.h>
#include <fcntl.h>
#include <signal.h>
#include <unistd.h>
#include <syslog.h>
#include <string.h>
#include <stdlib.h>
#include <getopt.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/wait.h>
#include <errno.h>
#include <pwd.h>

#define RUNNING_DIR	"/"
#define PIDFILE		"/var/run/daemonize.pid"
#define VARLOGFILE 	"/var/log/daemon.log"
#define PROGNAME	"daemonized"
#define DEFAULTUSER	"root"

char * pidfile = PIDFILE;
char * varlogfile = VARLOGFILE;
char * progname = PROGNAME;
char * user = PROGNAME;

void initialize_syslog(const char*pn) {
	openlog(pn,LOG_PID,LOG_DAEMON);
	syslog(LOG_INFO, "syslog connection opened");
}

void cleanup_syslog() {
	syslog(LOG_INFO, "syslog connection closed");
	closelog(); 
}

int killed = 0;
int killsignal = 0;
int pidfile_fd;
int varlogfile_fd;
int uid = 0; int gid = 0;
struct passwd *creds;

void signal_handler(sig)
int sig;
{
	killsignal = sig;
	switch(sig) {
	case SIGCHLD:
		syslog(LOG_INFO,"sigchild signal caught");
		break;
	case SIGHUP:
		syslog(LOG_INFO,"hangup signal caught");
		killed = 1;
		break;
	case SIGTERM:
		syslog(LOG_INFO,"terminate signal caught");
		killed = 1;
		break;
	case SIGINT:
		syslog(LOG_INFO,"keyboard interrupt signal caught");
		killed = 1;
		break;
	}
}

int daemonize(const char*prog_name)
{

	char str[10];
	int i;
	int bufsize=1024; char *buf = malloc(1024);
	
	umask( S_IWGRP | S_IROTH | S_IWOTH ); /* set newly created file permissions */
	
	/* test logfile */
	varlogfile_fd=open(varlogfile,O_RDWR|O_CREAT|O_APPEND,0666);
	if (varlogfile_fd == -1) {
		snprintf(buf,bufsize,"Could not open output file %s -- exiting",varlogfile); perror(buf);
		return 1; /* exitvalue */
	}
	if (uid != 0) {
		chown(varlogfile,uid,gid);
	}
	close(varlogfile_fd);
	pidfile_fd=open(pidfile,O_RDWR|O_CREAT,0666);
	if (pidfile_fd<0) {
		snprintf(buf,bufsize,"The PID file %s cannot be opened -- exiting",pidfile); perror(buf);
		return 2; /* exitvalue */
	}
	if (lockf(pidfile_fd,F_TEST,0)==1) {
		snprintf(buf,bufsize,"A daemon is already running (cannot lock PID file %s) -- exiting",pidfile); perror(buf);
		return 3; /* exitvalue */
	}
	close(pidfile_fd);
	
	if(getppid()==1) return 0; /* already a daemon */
	i=fork();
	if (i < 0) return 4; /* exitvalue */ /* fork error */
	if (i > 0) exit(0); /* parent exits */

	/* child (daemon) continues */
	setsid(); /* obtain a new process group */

	chdir(RUNNING_DIR); /* change running directory */
	 
	/* close FDs and reopen to logfile */
	for (i=getdtablesize();i>=0;--i) close(i); /* close all descriptors */
	varlogfile_fd=open(varlogfile,O_RDWR|O_APPEND,0666); dup(varlogfile_fd); dup(varlogfile_fd); /* handle standart I/O */
	initialize_syslog(prog_name); /* set up syslog */
	
	/* PID file */
	pidfile_fd=open(pidfile,O_RDWR|O_CREAT,0666);
	if (pidfile_fd<0) {
		syslog(LOG_ERR,"The PID file %s cannot be opened (%m) -- exiting",pidfile);
		return 2; /* exitvalue */
	}
	if (lockf(pidfile_fd,F_TLOCK,0)<0) {
		syslog(LOG_ERR,"A daemon is already running -- cannot lock PID file %s (%m) -- exiting",pidfile);
		return 3; /* exitvalue */
	}

	/* first instance continues */
	
	/* record pid to pidfile */
	sprintf(str,"%d\n",getpid());
	if (write(pidfile_fd,str,strlen(str)) < strlen(str)) {
		syslog(LOG_ERR,"Could not write PID into PID file %s (%m) -- exiting",pidfile);
		return 5; /* exitvalue */
	}
	signal(SIGTSTP,SIG_IGN); /* ignore tty signals */
	signal(SIGTTOU,SIG_IGN);
	signal(SIGTTIN,SIG_IGN);
	signal(SIGHUP,signal_handler); /* catch hangup signal */
	signal(SIGTERM,signal_handler); /* catch kill signal */
	signal(SIGINT,signal_handler); /* catch keyboard interrupt signal */
	
	return 0;
}

void cleanup() {
	cleanup_syslog();
	unlink(pidfile);
	close(pidfile_fd);
	close(varlogfile_fd);
}

void usage(char * cmdname) {
	fprintf (stderr,
		"Usage: %s [options...] -- <command> [command-specific arguments...]\n"
		"Daemonize any program.\n"
		"\n"
		"Options:\n"
		"\n"
		"	-l <logfile>:   log stdout/stderr to this *absolute* path (default "VARLOGFILE")\n"
		"	-u <username>:   setuid() to this user name before starting the program (default "DEFAULTUSER")\n"
		"	-p <pidfile>:   lock and write the PID to this *absolute* path (default "PIDFILE")\n"
		"	-n <progname>:  name the daemon assumes (default "PROGNAME")\n"
		"	-h: show this usage guide\n"
		"\n"
		"Exit status:\n"
		" 0      if daemonized correctly\n"
		" other  if an error took place\n"
		"", cmdname);
	exit(0);
}

int parse_args(int argc,char ** argv) {
	int index;
	int c;
	
// 	pidfile = PIDFILE;
// 	varlogfile = VARLOGFILE;
// 	progname = PROGNAME;
	
	opterr = 0;
	
	while ((c = getopt (argc, argv, "l:p:n:u:")) != -1)
		switch (c)
		{
			case 'l':
				varlogfile = optarg;
				break;
			case 'p':
				pidfile = optarg;
				break;
			case 'n':
				progname = optarg;
				break;
			case 'u':
				if (getuid() != 0) {
					fprintf (stderr, "-u can only be used by root.\nSee help with -h\n", user);
					exit(64);
				}
				user = optarg;
				creds = getpwnam(user);
				if (creds == NULL) {
					fprintf (stderr, "User %s was not found in the user database.\nSee help with -h\n", user);
					exit(63);
				}
				uid = creds->pw_uid; gid = creds->pw_gid;
				break;
// 			case 'h':
// 				break;
// 				usage(argv[0]); /* halts after this */
			case '?':
				if (optopt == '?' || optopt == 'h')
					usage(argv[0]); /* halts after this */
				if (optopt == 'l' || optopt == 'p' || optopt == 'n')
					fprintf (stderr, "Option -%c requires an argument.\nSee help with -h\n", optopt);
				else if (isprint (optopt))
					fprintf (stderr, "Unknown option `-%c'.\nSee help with -h\n", optopt);
				else
					fprintf (stderr, "Unknown option character `\\x%x'.\nSee help with -h\n", optopt);
				exit(64); /* exitvalue */
			default:
				abort ();
		}
	
	for (index = optind; index < argc; index++);

	if (index == optind) {
		fprintf (stderr, "You need to specify a command to run.\nSee help with -h\n", optopt);
		exit(64); /* exitvalue */
	}

	return optind;
}

int main(int argc, char** argv)
{
	/* parse command line arguments, we will use the first non-option one as the starting point */
	int i;
	char ** newargv = calloc(argc+1, sizeof(char**));
	int startat = parse_args(argc,argv);
	int newargc = argc - startat; 
	for (i = startat; i < argc; i++) { newargv[i-startat] = argv[i]; }

	/* try and daemonize */
	int daemonret = daemonize(progname);
	if (daemonret) exit(daemonret);
	syslog(LOG_INFO,"successfully daemonized");

	/* fork */
	int pid, wpid, status, execret;
	syslog(LOG_INFO,"starting %s in subprocess",newargv[0]);
	pid = fork();
	if (pid < 0) {
		/* failed to fork, damnit! */
		syslog(LOG_ERR,"could not fork to run %s as a child process (%m)",newargv[0]);
		exit(4); /* exitvalue */
	}
	else if (pid == 0) {
		/* child */
		if (uid != 0) {
			execret = setgid(gid);
			if (execret == -1) {
				syslog(LOG_ERR,"could not setgid() to gid %d",gid);
				exit(8); /* exitvalue */
			}
			execret = setuid(uid);
			if (execret == -1) {
				syslog(LOG_ERR,"could not setuid() to uid %d",uid);
				exit(8); /* exitvalue */
			}
		}
		execret = execvp(newargv[0],newargv);
		if (errno == 2) {
			syslog(LOG_ERR,"could not run program: no such file or directory");
			exit(127);
		}
		if (errno == 13) {
			syslog(LOG_ERR,"could not run program: permission denied");
			exit(126);
		}
		syslog(LOG_ERR,"could not run program: unknown reason");
		exit(255);
	}

	/* parent continues here */
	syslog(LOG_INFO,"successfully started subprocess -- PID %d",pid);
	int finalexit = 0;
	int waitret = 0;
	while (1) {
		if (killed) {
			kill(pid,killsignal);
			killed = 0;
		}
		waitret = waitpid(pid,&status,WNOHANG);
		if (waitret == pid) break;
		usleep(250000);
	}
	
	
	if WIFEXITED(status) {
		switch (WEXITSTATUS(status)) {
			case 0:
				syslog(LOG_INFO,"%s exited normally",newargv[0]);
				break;
			case 126:
				syslog(LOG_ERR,"%s: permission denied",newargv[0]);
				finalexit = 126; /* exitvalue */
				break;
			case 127:
				syslog(LOG_ERR,"%s: command not found",newargv[0]);
				finalexit = 127; /* exitvalue */
				break;
			default:
				syslog(LOG_INFO,"%s exited abnormally with status %d",newargv[0],WEXITSTATUS(status));
				finalexit = 6; /* exitvalue */
		}
	}
	if WIFSIGNALED(status) {
		syslog(LOG_INFO,"%s was killed with signal %d",newargv[0],WTERMSIG(status));
		finalexit = 7; /* exitvalue */
	}

	syslog(LOG_INFO,"shutting down");
	cleanup();
	exit(finalexit);
}

/* EOF */