Setgid example (cont)

Compile and set proper permissions

 # gcc -o shadow-reader shadow-reader.c
 # chgrp shadow shadow-reader
 # chmod g+s shadow-reader
 # ls -l shadow-reader
 -rwxr-sr-x  1 root shadow  17632 Sep 17 10:40 shadow-reader

Now, whenever someone runs 'shadow-reader' it will be able to access /etc/shadow:

 # ls -l /etc/shadow
 -rw-r-----  1 root shadow    827 Apr 25 10:40 /etc/shadow