直接看程式：

#include <stdio.h>

int main()
{
	printf("pid:%d, ppid:%d, uid:%d, gid:%d\n", getpid(), getppid(), getuid(), getgid());
	return 0;
}

     結果為：  [[email protected] learn_c]$ echo $$
2774
[[email protected] learn_c]$ id
uid=501(taoge) gid=502(taoge) groups=502(taoge),501(embed)
[

[email protected] learn_c]$ ./a.out 
pid:2898, ppid:2774, uid:501, gid:502
[[email protected] learn_c]$ su root
Password: 
[[email protected] learn_c]# echo &&
> 
> ^C
[[email protected] learn_c]# id
uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),4(adm),6(disk),10(wheel)
[

[email protected] learn_c]# ./a.out 
pid:2922, ppid:2905, uid:0, gid:0

[r[email protected] learn_c]# su taoge
[[email protected] learn_c]$ echo $$
2928
[[email protected] learn_c]$ id
uid=501(taoge) gid=502(taoge) groups=502(taoge),501(embed)
[[email protected] learn_c]$ ./a.out 
pid:2946, ppid:2928, uid:501, gid:502
[

[email protected] learn_c]$ 

     ok,  無需多說。