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PAM_FILTER(8)                             Linux-PAM Manual                             PAM_FILTER(8)



NAME
       pam_filter - PAM filter module

SYNOPSIS
       pam_filter.so [debug] [new_term] [non_term] run1|run2 filter [...]

DESCRIPTION
       This module is intended to be a platform for providing access to all of the input/output that
       passes between the user and the application. It is only suitable for tty-based and
       (stdin/stdout) applications.

       To function this module requires filters to be installed on the system. The single filter
       provided with the module simply transposes upper and lower case letters in the input and
       output streams. (This can be very annoying and is not kind to termcap based editors).

       Each component of the module has the potential to invoke the desired filter. The filter is
       always execv(2) with the privilege of the calling application and not that of the user. For
       this reason it cannot usually be killed by the user without closing their session.

OPTIONS
       debug
           Print debug information.

       new_term
           The default action of the filter is to set the PAM_TTY item to indicate the terminal that
           the user is using to connect to the application. This argument indicates that the filter
           should set PAM_TTY to the filtered pseudo-terminal.

       non_term
           don't try to set the PAM_TTY item.

       runX
           In order that the module can invoke a filter it should know when to invoke it. This
           argument is required to tell the filter when to do this.

           Permitted values for X are 1 and 2. These indicate the precise time that the filter is to
           be run. To understand this concept it will be useful to have read the pam(3) manual page.
           Basically, for each management group there are up to two ways of calling the module's
           functions. In the case of the authentication and session components there are actually
           two separate functions. For the case of authentication, these functions are
           pam_authenticate(3) and pam_setcred(3), here run1 means run the filter from the
           pam_authenticate function and run2 means run the filter from pam_setcred. In the case of
           the session modules, run1 implies that the filter is invoked at the pam_open_session(3)
           stage, and run2 for pam_close_session(3).

           For the case of the account component. Either run1 or run2 may be used.

           For the case of the password component, run1 is used to indicate that the filter is run
           on the first occasion of pam_chauthtok(3) (the PAM_PRELIM_CHECK phase) and run2 is used
           to indicate that the filter is run on the second occasion (the PAM_UPDATE_AUTHTOK phase).

       filter
           The full pathname of the filter to be run and any command line arguments that the filter
           might expect.

MODULE TYPES PROVIDED
       All module types (auth, account, password and session) are provided.

RETURN VALUES
       PAM_SUCCESS
           The new filter was set successfully.

       PAM_ABORT
           Critical error, immediate abort.

EXAMPLES
       Add the following line to /etc/pam.d/login to see how to configure login to transpose upper
       and lower case letters once the user has logged in:

                   session required pam_filter.so run1 /lib/security/pam_filter/upperLOWER



SEE ALSO
       pam.conf(5), pam.d(5), pam(7)

AUTHOR
       pam_filter was written by Andrew G. Morgan <morgan AT kernel.org>.



Linux-PAM Manual                             06/08/2020                                PAM_FILTER(8)