# phpman > info > pam_authenticate

[PAM_AUTHENTICATE(3)](https://www.chedong.com/phpMan.php/man/PAMAUTHENTICATE/3/markdown)            Linux-PAM Manual            [PAM_AUTHENTICATE(3)](https://www.chedong.com/phpMan.php/man/PAMAUTHENTICATE/3/markdown)

NAME
       pam_authenticate - account authentication

SYNOPSIS
       #include <security/pam_appl.h>

       int pam_authenticate(pam_handle_t *pamh, int flags);

DESCRIPTION
       The pam_authenticate function is used to authenticate the user. The
       user is required to provide an authentication token depending upon the
       authentication service, usually this is a password, but could also be a
       finger print.

       The PAM service module may request that the user enter their username
       via the conversation mechanism (see [pam_start(3)](https://www.chedong.com/phpMan.php/man/pamstart/3/markdown) and [pam_conv(3)](https://www.chedong.com/phpMan.php/man/pamconv/3/markdown)). The
       name of the authenticated user will be present in the PAM item
       PAM_USER. This item may be recovered with a call to [pam_get_item(3)](https://www.chedong.com/phpMan.php/man/pamgetitem/3/markdown).

       The pamh argument is an authentication handle obtained by a prior call
       to pam_start(). The flags argument is the binary or of zero or more of
       the following values:

       PAM_SILENT
           Do not emit any messages.

       PAM_DISALLOW_NULL_AUTHTOK
           The PAM module service should return PAM_AUTH_ERR if the user does
           not have a registered authentication token.

RETURN VALUES
       PAM_ABORT
           The application should exit immediately after calling [pam_end(3)](https://www.chedong.com/phpMan.php/man/pamend/3/markdown)
           first.

       PAM_AUTH_ERR
           The user was not authenticated.

       PAM_CRED_INSUFFICIENT
           For some reason the application does not have sufficient
           credentials to authenticate the user.

       PAM_AUTHINFO_UNAVAIL
           The modules were not able to access the authentication information.
           This might be due to a network or hardware failure etc.

       PAM_MAXTRIES
           One or more of the authentication modules has reached its limit of
           tries authenticating the user. Do not try again.

       PAM_SUCCESS
           The user was successfully authenticated.

       PAM_USER_UNKNOWN
           User unknown to authentication service.

SEE ALSO
       [pam_start(3)](https://www.chedong.com/phpMan.php/man/pamstart/3/markdown), [pam_setcred(3)](https://www.chedong.com/phpMan.php/man/pamsetcred/3/markdown), [pam_chauthtok(3)](https://www.chedong.com/phpMan.php/man/pamchauthtok/3/markdown), [pam_strerror(3)](https://www.chedong.com/phpMan.php/man/pamstrerror/3/markdown), [pam(7)](https://www.chedong.com/phpMan.php/man/pam/7/markdown)

Linux-PAM Manual                  06/08/2020               [PAM_AUTHENTICATE(3)](https://www.chedong.com/phpMan.php/man/PAMAUTHENTICATE/3/markdown)