linux守护进程、SIGHUP与nohup详解

  1 #include <stdio.h>
  2 #include <syslog.h>
  3 #include <errno.h>
  4 #include <unistd.h>
  5 #include <stdlib.h>
  6 #include <fcntl.h>
  7 #include <signal.h>
  8 #include <sys/types.h>
  9 #include <sys/stat.h>
 10 #include <sys/resource.h>
 11 
 12 #define PID_FILE "/var/run/sampled.pid"
 13 
 14 int sampled_running(){
 15     FILE * pidfile = fopen(PID_FILE,"r");
 16     pid_t pid;
 17     int ret ;
 18 
 19     if (! pidfile) {
 20         return 0;
 21     }
 22 
 23     ret = fscanf(pidfile,"%d",&pid);
 24     if (ret == EOF && ferror(pidfile) != 0){
 25         syslog(LOG_INFO,"Error open pid file %s",PID_FILE);
 26     }
 27 
 28     fclose(pidfile);
 29     
 30     // 检测进程是否存在
 31     if ( kill(pid , 0 ) ){
 32         syslog(LOG_INFO,"Remove a zombie pid file %s", PID_FILE);
 33         unlink(PID_FILE);
 34         return 0;
 35     }
 36 
 37     return pid;
 38 }
 39 
 40 pid_t sampled(){
 41     pid_t pid;
 42     struct rlimit rl;
 43     int fd,i;
 44 
 45     // 创建子进程，并退出当前父进程
 46     if((pid = fork()) < 0){
 47         syslog(LOG_INFO,"sampled : fork error");
 48         return -1;
 49     }
 50     if ( pid != 0) {
 51         //  父进程直接退出
 52         exit(0);
 53     }
 54 
 55     // 新建会话，成功返回值是会话首进程id，进程组id ，首进程id
 56     pid = setsid();
 57 
 58     if ( pid < -1 ){
 59         syslog(LOG_INFO,"sampled : setsid error");
 60         return -1;
 61     }
 62 
 63     // 将工作目录切换到根目录
 64     if ( chdir("/") < 0 ) {
 65         syslog(LOG_INFO,"sampled : chidr error");
 66         return -1;
 67     }
 68 
 69     // 关闭所有打开的句柄，如果确定父进程未打开过句柄，此步可以不做
 70     if ( rl.rlim_max == RLIM_INFINITY ){
 71         rl.rlim_max = 1024;
 72     }
 73     for(i = 0 ; i < rl.rlim_max; i ++) {
 74         close(i);
 75     }
 76 
 77     // 重定向输入输出错误
 78     fd = open("/dev/null",O_RDWR,0);
 79     if(fd != -1){
 80         dup2(fd,STDIN_FILENO);
 81         dup2(fd,STDOUT_FILENO);
 82         dup2(fd,STDERR_FILENO);
 83         if (fd > 2){
 84             close(fd);
 85         }
 86     }
 87     
 88     // 消除文件掩码
 89     umask(0);
 90     return 0;
 91 }
 92 
 93 int pidfile_write(){
 94     // 这里不用fopen直接打开文件是不想创建666权限的文件
 95     FILE * pidfile = NULL;
 96     int pidfilefd = creat(PID_FILE,S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH);
 97     if(pidfilefd != -1){
 98         pidfile = fdopen(pidfilefd,"w");
 99     }
100 
101     if (! pidfile){
102         syslog(LOG_INFO,"pidfile write : can't open pidfile:%s",PID_FILE);
103         return 0;
104     }
105     fprintf(pidfile,"%d",getpid());
106     fclose(pidfile);
107     return 1;
108 }
109 
110 int main(){
111     int err,signo;
112     sigset_t mask;
113 
114     if (sampled_running() > 0 ){
115          exit(0);
116     }
117 
118     if ( sampled() != 0 ){
119 
120     }
121     // 写记录锁文件  
122     if (pidfile_write() <= 0) {
123         exit(0);
124     }
125 
126     while(1) {
127         // 捕捉信号
128         err = sigwait(&mask,&signo);
129         if( err != 0  ){
130             syslog(LOG_INFO,"sigwait error : %d",err);
131             exit(1);
132         }
133         switch (signo){
134             default :
135                 syslog(LOG_INFO,"unexpected signal %d \n",signo);
136                 break;
137             case SIGTERM:
138                 syslog(LOG_INFO,"got SIGTERM. exiting");
139                 exit(0);
140         }
141 
142     }
143 
144 }