調用setsid函數的進程需要滿足以下條件：

1. 不是組長進程

2. 有對應的創建session權限

調用setsid函數后的進程：

1. 成為一個組的組長進程

2. 成為一個會話的會話首進程

3. 放棄了控制終端

#include <stdio.h>#include <unistd.h>#include <stdlib.h>int main(int argc, char *argv[]){	pid_t pid;		pid = fork();		if (pid < 0)	{		perror("fork");		return -1;	}	else if (pid == 0)	{		PRintf("before====/n");		printf("pid = %d/n", (int)getpid());		printf("gid = %d/n", (int)getpgrp());		printf("sid = %d/n", (int)getsid(getpid()));				setsid();				printf("after====/n");		printf("pid = %d/n", (int)getpid());		printf("gid = %d/n", (int)getpgrp());		printf("sid = %d/n", (int)getsid(getpid()));				sleep(5);	}	else	{		printf("parent-------/n");		printf("pid = %d/n", getpid());		printf("gid = %d/n", getgid());		printf("sid = %d/n", getsid());		waitpid(pid, NULL, 0);	}		return 0;}運行結果：
parent-------pid = 13227gid = 0sid = 12710before====pid = 13228gid = 13227sid = 12710after====pid = 13228gid = 13228sid = 13228