关于Linux中使用geteuid()返回值uid_t参数值的问题

[青冥遗落]

刚学不久linux，写who am i的时候发现网上不少答案用的都是geteuid（）获得有效用户，看了下man帮助，这么显示的：

GETUID(2)                  Linux Programmer's Manual                 GETUID(2)

NAME
       getuid, geteuid - get user identity

SYNOPSIS
       #include <unistd.h>
       #include <sys/types.h>

       uid_t getuid(void);
       uid_t geteuid(void);

DESCRIPTION
       getuid() returns the real user ID of the calling process.

       geteuid() returns the effective user ID of the calling process.

ERRORS
       These functions are always successful.

CONFORMING TO
       POSIX.1-2001, 4.3BSD.

NOTES
   History
       In  UNIX  V6  the  getuid()  call  returned (euid << 8) + uid.  UNIX V7
       introduced separate calls getuid() and geteuid().

       The original Linux getuid() and geteuid() system calls  supported  only
       16-bit   user  IDs.   Subsequently,  Linux  2.4  added  getuid32()  and
       geteuid32(), supporting 32-bit IDs.  The glibc getuid()  and  geteuid()
       wrapper  functions transparently deal with the variations across kernel
       versions.

SEE ALSO
       getresuid(2), setreuid(2), setuid(2), credentials(7)

COLOPHON
       This page is part of release 3.54 of the Linux  man-pages  project.   A
       description  of  the project, and information about reporting bugs, can
 Manual page geteuid(2) line 1 (press h for help or q to quit)

比较疑惑uid_t这个返回类型，我不清楚会返回几个用户的信息，想问问首先有效用户应该不会只有自己吧，另外返回的话每次调用geteuid()会返回几个用户的信息呢？还是要怎么依次访问？

[cl55]

这两个都只返回一个用户。 getuid 返回当前进程的用户 geteuid 返回有效用户,也就是说被运行的程序以它的owner做为有效用户，所以运行这个程序的用户可以间接访问到有效用户才能访问到的资源

[zhxianbin]

typedef __kernel_uid32_t uid_t; typedef unsigned int __kernel_uid32_t; uid_t 是 unsigned int 类型的