Blame SOURCES/vsftpd.pam

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#%PAM-1.0
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session    optional     pam_keyinit.so    force revoke
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auth       required	pam_listfile.so item=user sense=deny file=/etc/vsftpd/ftpusers onerr=succeed
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auth       required	pam_shells.so
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auth       include	password-auth
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account    include	password-auth
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session    required     pam_loginuid.so
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session    include	password-auth