In response to a call to pam_chauthtok() the PAM framework calls pam_sm_chauthtok(3PAM) from the modules listed in the pam.conf(4) file. The password management provider supplies the back-end functionality for this interface function.

The pam_sm_chauthtok() function changes the authentication token associated with a particular user referenced by the authentication handle pamh.

The following flag may be passed to pam_chauthtok():

PAM_SILENT

The password service should not generate any messages.

PAM_CHANGE_EXPIRED_AUTHTOK

The password service should only update those passwords that have aged. If this flag is not passed, the password service should update all passwords.

PAM_PRELIM_CHECK

The password service should only perform preliminary checks. No passwords should be updated.

PAM_UPDATE_AUTHTOK

The password service should update passwords.

Note that PAM_PRELIM_CHECK and PAM_UPDATE_AUTHTOK cannot be set at the same time.

Upon successful completion of the call, the authentication token of the user will be ready for change or will be changed, depending upon the flag, in accordance with the authentication scheme configured within the system.

The argc argument represents the number of module options passed in from the configuration file pam.conf(4). The argv argument specifies the module options, which are interpreted and processed by the password management service. Please refer to the specific module man pages for the various available options.

It is the responsibility of pam_sm_chauthtok() to determine if the new password meets certain strength requirements. pam_sm_chauthtok() may continue to re-prompt the user (for a limited number of times) for a new password until the password entered meets the strength requirements.

Before returning, pam_sm_chauthtok() should call pam_get_item() and retrieve both PAM_AUTHTOK and PAM_OLDAUTHTOK. If both are NULL, pam_sm_chauthtok() should set them to the new and old passwords as entered by the user.

Upon successful completion, PAM_SUCCESS must be returned. The following values may also be returned:

PAM_PERM_DENIED

No permission.

PAM_AUTHTOK_ERR

Authentication token manipulation error.

PAM_AUTHTOK_RECOVERY_ERR

Old authentication token cannot be recovered.

PAM_AUTHTOK_LOCK_BUSY

Authentication token lock busy.

PAM_AUTHTOK_DISABLE_AGING

Authentication token aging disabled.

PAM_USER_UNKNOWN

User unknown to password service.

PAM_TRY_AGAIN

Preliminary check by password service failed.

See attributes(5) for description of the following attributes:

ping(1M), pam(3PAM), pam_chauthtok(3PAM), pam_get_data(3PAM), pam_get_item(3PAM), pam_set_data(3PAM), libpam(3LIB), pam.conf(4), attributes(5)

The PAM framework invokes the password services twice. The first time the modules are invoked with the flag, PAM_PRELIM_CHECK. During this stage, the password modules should only perform preliminary checks. For example, they may ping remote name services to see if they are ready for updates. If a password module detects a transient error such as a remote name service temporarily down, it should return PAM_TRY_AGAIN to the PAM framework, which will immediately return the error back to the application. If all password modules pass the preliminary check, the PAM framework invokes the password services again with the flag, PAM_UPDATE_AUTHTOK. During this stage, each password module should proceed to update the appropriate password. Any error will again be reported back to application.

If a service module receives the flag PAM_CHANGE_EXPIRED_AUTHTOK, it should check whether the password has aged or expired. If the password has aged or expired, then the service module should proceed to update the password. If the status indicates that the password has not yet aged or expired, then the password module should return PAM_IGNORE.

If a user's password has aged or expired, a PAM account module could save this information as state in the authentication handle, pamh, using pam_set_data(). The related password management module could retrieve this information using pam_get_data() to determine whether or not it should prompt the user to update the password for this particular module.

The interfaces in libpam are MT-Safe only if each thread within the multithreaded application uses its own PAM handle.