Some guru's code for daemon._symdaemon-优快云博客

本文链接：https://blog.youkuaiyun.com/symield/article/details/191028

此博客给出一段C语言代码，包含多个头文件引入，定义了日志记录函数和信号处理函数，实现了守护进程的创建，包括fork、setsid等操作，还对多个信号进行处理，最后在主函数中调用守护进程函数并进入无限循环。

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#include <stdio.h>
#include <fcntl.h>
#include <signal.h>
#include <unistd.h>

#define RUNNING_DIR "/tmp"
#define LOCK_FILE "exampled.lock"
#define LOG_FILE "exampled.log"

void log_message(char *filename,char *message){
   FILE *logfile;
   logfile=fopen(filename,"a");
   if(!logfile)
        return;
   fprintf(logfile,"%s/n",message);
   fclose(logfile);
}

void signal_handler(int sig){
   switch(sig){
   case SIGHUP:
        log_message(LOG_FILE,"hangup siganl catched");
        signal(SIGHUP,signal_handler);
        break;
   case SIGTERM:
        log_message(LOG_FILE,"terminate signal catched");
        exit(0);
        break;
   }
}
void daemonize(){
   int i,lfp;
   char str[10];

   if(getppid()==1) return ;/* already a daemon*/
   i=fork();
   if(i<0)exit(1);/*fork error*/
   if(i>0)exit(0); /*parent exits*/

setsid();
for(i=getdtablesize();i>=0;--i)close(i); /*close all descriptors*/

   i=open("/dev/null",O_RDWR);
   dup(i);
   dup(i);
   umask(027);
   chdir(RUNNING_DIR);

   lfp=open(LOCK_FILE,O_RDWR|O_CREAT,0640);
   if(lfp<0)exit(1);
   if(lockf(lfp,F_TLOCK,0)<0)
        exit(0);/*can't lock*/
   /*first instance continues*/
   sprintf(str,"%d/n",getpid());
   write(lfp,str,strlen(str));

   signal(SIGCHLD,SIG_IGN);
   signal(SIGTSTP,SIG_IGN);
   signal(SIGTTOU,SIG_IGN);
   signal(SIGTTIN,SIG_IGN);
   signal(SIGHUP,signal_handler);
   signal(SIGTERM,signal_handler);
}

int main(void){
daemonize();
while(1) sleep(1);
}