unix_chkpwd is a helper program for the pam_unix module that verifies
the password of the current user. It also checks password and account
expiration dates in shadow. It is not intended to be run directly from
the command line and logs a security violation if done so.
It is typically installed setuid root or setgid shadow.
The interface of the helper - command line options, and input/output
data format are internal to the pam_unix module and it should not be
called directly from applications.
Written by Andrew Morgan and other various people.
Linux-PAM Manual 06/04/2011 UNIX_CHKPWD(8)
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