trap sighup

shell进程只会向由它创建的进程组发送的SIGHUP信号，不会向不是由它创建的进程组发送SIGHUP信号。
使用alarm设置一个定时器来发送SIGALRM信号，如果一个进程接收到SIGALRM信号而不处理时会导致进程终止。

[e-mail]:~/test/signal>more trap_sighup1.c
#include <unistd.h>
#include <signal.h>
#include <stdio.h>
static void handler(int sig)
{

}

int main(int argc, char *argv[])
{
    pid_t childPid;
    struct sigaction sa;

    setbuf(stdout,NULL);

    sigemptyset(&sa.sa_mask);
    sa.sa_flags = 0;
    sa.sa_handler = handler;
    if(sigaction(SIGHUP,&sa,NULL) == -1) {
        printf("sigaction error\n");
        return -1;
    }

    childPid = fork();

    if(childPid < 0){
        printf("fork error\n");
        return -1;
    }
    if(childPid == 0 && argc > 1) {
        if(setpgid(0,0) < 0) {
            printf("etpgid error\n");
            return -1;
        }
    }

    printf("PID = %ld,PPID = %ld,PGID = %ld,SID = %ld\n",(long)getpid(),
            (long)getppid(),(long)getpgrp(),(long)getsid(0));

    alarm(60);

    for(;;) {
        pause();
        printf("%ld catch sighup\n",(long)getpid());
    }
}

[e-mail]:~/test/signal>echo $$
10231
[e-mail]:~/test/signal>gcc -g trap_sighup1.c -o trap_sighup1   
[e-mail]:~/test/signal>./trap_sighup1 > trap_sighup1_log 2>&1 &
[1] 12260
[e-mail]:~/test/signal>./trap_sighup1 x > trap_sighup_x_log 2>&1

接着关闭终端
重新连接终端，查看对应的log文件。

[e-mail]:~/test/signal>more trap_sighup1_log 
PID = 12260,PPID = 10231,PGID = 12260,SID = 10231
PID = 12261,PPID = 12260,PGID = 12260,SID = 10231
12261 catch sighup
12260 catch sighup
[e-mail]:~/test/signal>more trap_sighup2_log  
trap_sighup2_log: No such file or directory
[e-mail]:~/test/signal>more trap_sighup_x_log  
PID = 12267,PPID = 10231,PGID = 12267,SID = 10231
PID = 12268,PPID = 12267,PGID = 12268,SID = 10231
12267 catch sighup