Set User Id - ggubuk97/apue GitHub Wiki

bart@bear:/usr/bin$ cd /usr/bin/
bart@bear:/usr/bin$ ls -al passwd
-rwsr-xr-x 1 root root 42824 Sep 13  2012 passwd

bart@bear:~/ws/bart$ ll
total 24
drwxrwxr-x 2 bart bart 4096 Oct  8 09:08 ./
drwxrwxr-x 8 bart bart 4096 Oct  7 21:12 ../
-rwxrwxr-x 1 bart bart 8542 Oct  7 22:04 a.out*
-rw-rw-rw- 1 bart bart  245 Oct  8 09:08 passwd.c
bart@bear:~/ws/bart$ 
bart@bear:~/ws/bart$ cat passwd.c 

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <unistd.h>

int main(int argc, char* argv[])
{
    struct stat buf;
    if (stat("passwd.c", &buf) < 0) {
        printf("error\n");
    }

    chmod("passwd.c", buf.st_mode | S_ISUID);
}

bart@bear:~/ws/bart$ ./a.out 
bart@bear:~/ws/bart$ ll
total 24
drwxrwxr-x 2 bart bart 4096 Oct  8 09:08 ./
drwxrwxr-x 8 bart bart 4096 Oct  7 21:12 ../
-rwxrwxr-x 1 bart bart 8542 Oct  7 22:04 a.out*
-rwSrw-rw- 1 bart bart  245 Oct  8 09:08 passwd.c