可执行文件上的setuid似乎不起作用

我写了一个小的C实用程序,killSPR用来杀死RHEL盒子上的以下进程.这个想法适用于登​​录这个linux盒子的人能够使用这个实用程序杀死下面提到的进程(这不起作用 - 如下所述).

cadmn@rhel /tmp > ps -eaf | grep -v grep | grep " SPR "  
cadmn    5822  5821 99 17:19 ?        00:33:13 SPR 4 cadmn  
cadmn   10466 10465 99 17:25 ?        00:26:34 SPR 4 cadmn  
cadmn   13431 13430 99 17:32 ?        00:19:55 SPR 4 cadmn  
cadmn   17320 17319 99 17:39 ?        00:13:04 SPR 4 cadmn  
cadmn   20589 20588 99 16:50 ?        01:01:30 SPR 4 cadmn  
cadmn   22084 22083 99 17:45 ?        00:06:34 SPR 4 cadmn  
cadmn@rhel /tmp >  

该实用程序由用户拥有cadmn(运行这些进程)并在其上设置setuid标志(如下所示).

cadmn@rhel /tmp > ls -l killSPR  
-rwsr-xr-x 1 cadmn cusers 9925 Dec 17 17:51 killSPR  
cadmn@rhel /tmp > 

C代码如下:

/*  
 * Program Name: killSPR.c  
 * Description: A simple program that kills all SPR processes that  
 * run as user cadmn  
 */  
#include   
int main()  
{  
    char *input;  
    printf("Before you proceed, find out under which ID I'm running. Hit enter when you are done...");  
    fgets(input, 2, stdin);  

    const char *killCmd = "kill -9 $(ps -eaf | grep -v grep | grep \" SPR \" | awk '{print $2}')";  
    system(killCmd);  
    return 0;  
} 

用户(pmn)cadmn尝试使用此实用程序杀死上述进程并且失败(如下所示):

pmn@rhel /tmp > ./killSPR  
Before you proceed, find out under which ID I'm running. Hit enter when you are done...  
sh: line 0: kill: (5822) - Operation not permitted  
sh: line 0: kill: (10466) - Operation not permitted  
sh: line 0: kill: (13431) - Operation not permitted  
sh: line 0: kill: (17320) - Operation not permitted  
sh: line 0: kill: (20589) - Operation not permitted  
sh: line 0: kill: (22084) - Operation not permitted  
pmn@rhel /tmp >  

当用户等待上面的输入时,killSPR检查该过程并且看作是以用户身份运行cadmn(如下所示),尽管killSPR无法终止进程.

cadmn@rhel /tmp > ps -eaf | grep -v grep | grep killSPR  
cadmn   24851 22918  0 17:51 pts/36   00:00:00 ./killSPR  
cadmn@rhel /tmp >

顺便说一句,没有一个主分区有什么nosuid对他们

pmn@rhel /tmp > mount | grep nosuid
pmn@rhel /tmp >

可执行文件上的setuid标志似乎没有所需的效果.我在这里错过了什么？我误解了setuid是如何工作的吗？