December 2013
Intermediate to advanced
496 pages
8h 57m
Chinese
Content preview from LINUX系統程式設計 第二版
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第五章
以 HP-UX 的手法變更用戶和群組的識別碼
你可能會覺得情況越來越混亂，就連 HP-UX（Hewlett-Packard 的 Unix 系統）也提供了
自己的機制，以便用於設定一個行程的用戶和群組識別碼。Linux 隨後也提供了這些介
面，如果你想要維持 HP-UX 的移植性，這會很有用：
#define _GNU_SOURCE
#include <unistd.h>
int setresuid (uid_t ruid, uid_t euid, uid_t suid);
int setresgid (gid_t rgid, gid_t egid, gid_t sgid);
setresuid()
可用於把真實、有效以及暫存的用戶識別碼分別設定成
ruid
、
euid
以及
suid
。若把任何參數值設定成
-1
，則相對應的用戶識別碼會維持不變。
root
用戶可以把任何的用戶識別碼設定成任何值。非 root 用戶可以把任何的用戶識別碼
設定成當前之真實、有效或暫存的用戶識別碼。執行成功時，
setuid()
會傳回
0
。發生
錯誤時，則會傳回
-1
並把
errno
設定成下面其中一個值：
EAGAIN
uid
與真實用戶識別碼不相符，而且把真實用戶識別碼設定成
uid
，會使得用戶逾越
其
NPROC
rlimit（用於指定一個用戶所能擁有之行程的數目）。
EPERM
用戶不是
root
，而且企圖把真實、有效或暫存的用戶識別碼設定成與當前之真實、
有效或暫存的用戶識別碼不相符的值。
前面的討論同樣適用於群組—僅需要把
setresuid() ...
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