pam_mkhomedir doesn't work for su?

[pam-list at redhat.com (Chen Min)]

Hi,

 I use PAM-0.75 and OpenLDAP to do authentication on Redhat 7.3. Here is my
system-auth file:

auth        required      /lib/security/pam_env.so
auth        sufficient      /lib/security/pam_unix.so likeauth nullok
auth     [default=die success=ok user_unknown=ignore
authinfo_unavail=ignore]  /lib/security/pam_ldap.so use_first_pass
auth        required      /lib/security/pam_deny.so

account     required      /lib/security/pam_unix.so
account     [default=die success=ok user_unknown=ignore
authinfo_unavail=ignore]  /lib/security/pam_ldap.so

password    required      /lib/security/pam_cracklib.so retry=3 type=
password    sufficient    /lib/security/pam_unix.so nullok use_authtok md5
shadow
password    sufficient    /lib/security/pam_ldap.so use_authtok
password    required      /lib/security/pam_deny.so

session     optional      /lib/security/pam_mkhomedir.so skel=/etc/skel
umask=0022
session     required      /lib/security/pam_limits.so
session     required      /lib/security/pam_unix.so
session     optional      /lib/security/pam_ldap.so

 pam_mkhomedire.so is added to create home directory for LDAP user. It works
fine for ssh and console login, then I tried su
        #su ppp
        Creating directory '/home/ppp'.
	  $
 Open /home directory, ppp isn't there. In order to get error message from
pam_mkhomedire.so, change to
session     optional      /lib/security/pam_mkhomedir.so skel=/etc/skel
umask=0022 debug

it print out a message: unknown option, debug.

Have any idea?

Thanks in advanced

Min