在GNU libc关于orphaned process groups的手册中,它提到:
“process groups that continue running even after the session leader
has terminated are marked as orphaned process groups.
When a process group becomes an orphan, its processes are sent a SIGHUP
signal. Ordinarily, this causes the processes to terminate. However,
if a program ignores this signal or establishes a handler for it
(see Signal Handling), it can continue running as in the orphan process
group even after its controlling process terminates; but it still
cannot access the terminal any more. ”
我编写了一个测试程序,但当进程组成为一个孤儿时,它的进程没有收到SIGHUP信号 . 我想知道为什么?
#include <errno.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <unistd.h>
static void
sig_hup(int signo) //**never get called ???**
{
printf("SIGHUP received, pid = %ld\n", (long)getpid());
}
static void
pr_ids(char *name)
{
printf("%s: pid = %ld, ppid = %ld, pgrp = %ld, tpgrp = %ld\n",
name, (long)getpid(), (long)getppid(), (long)getpgrp(),
(long)tcgetpgrp(STDIN_FILENO));
fflush(stdout);
}
int
main(void)
{
char c;
pid_t pid;
pr_ids("parent");
pid = fork();
if (pid > 0) { // parent
sleep(5);
exit(0); // parent exit;
} else {
pr_ids("child");
setsid(); //create new session, and "child" becomes the session leader
pid = fork();
if(pid>0) {
sleep(20);
exit(0); // "child" exit
// so the process group become an orphan process group
}
else{
pr_ids("grandson");
signal(SIGHUP, sig_hup); // establish signal handler
sleep(60); // now becoming orphan process group
printf("end\n");
}
}
exit(0);
}
2 回答
该文档部分专门讨论了一个进程的控制终端的丢失 - 通常是通过调制解调器挂起或虚拟等效(结束ssh会话等) . (我认为文件中的措词可以在这里改进) . 当你在这里使用
setsid()
时,你会在setsid()
返回时放弃对控制终端的访问,因此没有控制终端从那里输掉 .你可以
open()
一个tty设备(比如pty slave)来获得一个控制终端(注意你可能还需要做一些额外的操作 - FreeBSD需要一个TIOCSCTTY
ioctl),然后再次失去它,然后你应该得到它SIGHUP
信号 .孤立的进程组获得SIGHUP,然后是SIGCONT,如果它们在孤立时被停止 .
睡眠不够,你需要:
除此之外,如果孤立是由
setsid()
或setprgrp()
引起的,POSIX不要求发送SIGHUP和SIGCONT,因为它不是由一个无意识不知道作业控制的退出进程引起的(参见http://pubs.opengroup.org/onlinepubs/9699919799/functions/_exit.html) .但是,使用
kill(getpid(), SIGSTOP)
而不是孩子中的sleep(60)
,即使您没有调用setsid()
,您的程序也会获得已停止的孤儿 .在父母去世(5s)后,应该让孩子获得一个SIGHUP .