On a server running CentOS 6.2 x86_64, Plesk 10.4.4 MU#22 and psa-proftpd-1.3.4a-1.el6.art.x86_64 /var/log/secure contains lots of messages like these:
Feb 25 18:32:26 hostname proftpd: PAM unable to dlopen(/lib64/security/pam_stack.so): /lib64/security/pam_stack.so: cannot open shared object file: No such file or directory
Feb 25 18:32:26 hostname proftpd: PAM adding faulty module: /lib64/security/pam_stack.so
There is no file called /lib64/security/pam_stack.so on this server. /etc/pam.d/proftpd (owned by the psa-proftpd package) does refer to pam_stack:
# cat /etc/pam.d/proftpd
auth required pam_listfile.so item=user sense=deny file=/etc/ftpusers onerr=succeed
auth required pam_stack.so service=system-auth
auth required pam_shells.so
account required pam_stack.so service=system-auth
session required pam_stack.so service=system-auth
I noticed that on EL5 x86_64 /lib64/security/pam_stack.so is part of the pam RPM, but on EL6 it's not. Is this a bug in the psa-proftpd package?
P.S. I see /etc/pam.d/imap and /etc/pam.d/pop3 also refer to pam_stack.so.