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man pages section 7: Standards, Environments, Macros, Character Sets, and Miscellany

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Updated: Wednesday, January 24, 2018



pam_unix_auth - PAM authentication module for UNIX




The pam_unix_auth module implements pam_sm_authenticate(), which provides functionality to the PAM authentication stack. It provides functions that use crypt(3C) to verify that the password contained in the PAM item PAM_AUTHTOK is the correct password for the user specified in the item PAM_USER.

If PAM_AUSER and PAM_USER are both specified and PAM_USER is a role, the user_attr(5) keyword roleauth is checked to determine if the password that is checked is for the role (PAM_USER) or the assuming user (PAM_AUSER). If PAM_REPOSITORY is specified, the user's pass word is fetched from that repository. Otherwise, the default nsswitch.conf(5) repository is searched for that user.

For accounts in the name services which support automatic account locking, the account can be configured to be automatically locked (see user_attr(5) and policy.conf(5)) after multiple failed login attempts. For accounts that are configured for automatic locking, if authentication failure is to be returned, the failed login counter is incremented upon each failure. If the number of successive failures equals or exceeds the configured value, the account is locked and PAM_MAXTRIES is returned. The files (see passwd(5) and shadow(5)) and ldap (when configured with enableShadowUpdate true, see ldapclient(8)), repositories support automatic account locking. A successful authentication by this module clears the failed login counter and reports the number of failed attempts since the last successful authentication. Accounts that have been locked, may be configured to be automatically unlocked upon successful authentication by configuring an unlock time (see user_attr(5) and policy.conf(5)).

Authentication service modules must implement both pam_sm_authenticate() and pam_sm_setcred(). To allow the authentication portion of UNIX authentication to be replaced, pam_sm_setcred() in this module always returns PAM_IGNORE . This module should be stacked with pam_unix_cred(7) to ensure a successful return from pam_setcred(3PAM).

The following options can be passed to the module:


Turn off warning messages.


If the account authority for the user, as specified by PAM_USER, is a server, do not apply the UNIX policy from the passwd entry in the name service switch.


Regardless of the automatic account locking setting for the account, do not lock the account, increment or clear the failed login count. The nolock option allows for exempting account locking on a per service basis.


The following error codes are returned from pam_sm_authenticate():


Authentication failure.


Memory buffer error.


Ignores module, not participating in result.


Maximum number of retries exceeded.


Permission denied.


Successfully obtains authentication token.


System error.


No account present for user.

The following error codes are returned from pam_sm_setcred():


Ignores this module regardless of the control flag.


See attributes(7) for descriptions of the following attributes:

Interface Stability
MT Level
MT-Safe with exceptions

See Also

login(1), passwd(1), crypt(3C), syslog(3C), libpam(3LIB), pam(3PAM), pam_authenticate(3PAM), pam_setcred(3PAM), nsswitch.conf(5), pam.conf(5), passwd(5), policy.conf(5), shadow(5), user_attr(5), attributes(7), pam_authtok_check(7), pam_authtok_get(7), pam_authtok_store(7), pam_dhkeys(7), pam_passwd_auth(7), pam_unix_account(7), pam_unix_session(7), ldapclient(8), roleadd(8), rolemod(8), useradd(8), usermod(8)


The interfaces in libpam(3LIB) are MT-Safe only if each thread within the multi-threaded application uses its own PAM handle.

If the PAM_REPOSITORY item_type is set and a service module does not recognize the type, the service module does not process any information, and returns PAM_IGNORE. If the PAM_REPOSITORY item_type is not set, a service module performs its default action.