C言語でラズパイのデーモンを作るときの補助関数とスケルトン

daemonize.c

#include <stdio.h>
#include <unistd.h>
#include <stdarg.h>
#include <signal.h>
#include <syslog.h>

static int daemonized = 0; /* daemonized flag */

int daemonize(
  const char* pidfilepath,
  const char *syslog_ident,
  int syslog_option,
  int syslog_facility)
{
  daemonized = 0; /* initialize */
  if (daemon(0, 0) != -1) {

    /* success to daemonize. */
    daemonized = 1;
	  
    /* open syslog */
    if(syslog_ident) {
      openlog(syslog_ident, syslog_option, syslog_facility);
    }

    /* write daemon pid to the file */
    if(pidfilepath) {
      FILE* pidfile = fopen(pidfilepath, "w+");
      if (pidfile) {
        int pid = getpid();
        fprintf(pidfile, "%d\n", pid);
        fclose(pidfile);
      } else {
        syslog(LOG_ERR,
          "daemonize() : failed to write pid.\n");
      }
    }
  }
  return daemonized;
}

daemonize.h

#ifdef __cplusplus__
extern "C" {
#endif

/*!
 * create a typical daemon process.
 *
 * @param [in] pidfilepath      The pid file pathname.
 *                              If NULL, it will never record.
 * @param [in] syslog_ident     syslog ident.
 * @param [in] syslog_option    syslog option.
 * @param [in] syslog_facility  syslog facility.
 * @return this function        1:a daemon created, 0: error
 */
int daemonize(
  const char* pidfilepath,
  const char *syslog_ident,
  int syslog_option,
  int syslog_facility);

#ifdef __cplusplus__
}
#endif

mydaemon.c

#include <stdio.h>
#include <unistd.h>
#include <syslog.h>
#include "daemonize.h"

/* The following codes are only sample */
static volatile int sigterm = 0;
static void handle_sigterm(int sig) { sigterm = 1; }
static int mydaemon( void )
{
  syslog(LOG_INFO, "mydaemon started.\n");
  signal(SIGTERM, handle_sigterm);
  while(!sigterm) {
    /*
     * Here's cyclic daemon codes.
     */
    usleep(1000000);
  }
  syslog(LOG_INFO, "mydaemon stopped.\n");
  return 0;
}
int main(int argc, char* argv[])
{
  if(!daemonize("/var/run/mydaemon.pid",
    "daemon", LOG_PID, LOG_DAEMON))
  {
    fprintf(stderr, "failed to daemonize.\n");
    return 2; /* fail to start daemon */
  }
  return mydaemon();
}