hi guys, i've found a way to make use of the new password. copy the /etc/shadow, /etc/passwd, /etc/group to /home/chroot/./etc/
Make sure password field in passwd file is x which indicates that the real password is stored in the shadow file.
when the chrooted testuser issues passwd command and create a new password, it would change the password value stored in the /home/chroot/./etc/shadow file. when he log in back again using the new password, the system won't recognize it because it compares the password with the one stored in /etc/shadow.
so my idea is to create a patch file using diff command from the /home/chroot/./etc/shadow and then applied it to /etc/shadow.
chmod 400 /etc/shadow
chmod 400 /home/chroot/./etc/shadow
diff -u /etc/shadow /home/chroot/etc/shadow > shadow.patch
patch -b /etc/shadow /home/chroot/etc/shadow.patch
put the last two commands in the cron job......
it works perfectly now for me.... thank's to you guys......