man unix_chkpwd (Administration système) - check the password of the invoking user
NAME
unix_chkpwd - check the password of the invoking user
SYNOPSIS
<not invoked manually>
DESCRIPTION
A helper binary for the pam_unix module, unix_chkpwd, is provided to check the user's password when it is stored in a read protected database, such as shadow'd passwords. This binary is very simple and will only check the password of the user invoking it. It is called transparently on behalf of the user by the authenticating component of the pam_unix module. In this way it is possible for applications like xlock to work work without being setuid root.
USAGE
This program is not intended to be called directly by users and will log to syslog if it is called improperly (i.e., by someone trying to exploit it).