setuid、setgid - set user identity
作用
能改变 real ID, effective ID, saved set-user-ID
#include <sys/types.h>
#include <unistd.h>
int setuid(uid_t uid);
int setgid(gid_t gid);
//Return: 0 if OK, -1 on error
具体能改变哪些ID取决于下图
seteuid、setegid
仅仅影响effective user ID and group ID
seteuid, setegid - set effective user or group ID
#include <sys/types.h>
#include <unistd.h>
int seteuid(uid_t euid);
int setegid(gid_t egid);
//Both return: 0 if OK, -1 on error
Group IDs
对于Group IDs内容都是相同的