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

       pam_filter - PAM filter module

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

       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.

           Print debug information.

           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.

           don't try to set the PAM_TTY item.

           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

           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

           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

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

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

           The new filter was set successfully.

           Critical error, immediate abort.

       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 run1 /lib/security/pam_filter/upperLOWER

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

       pam_filter was written by Andrew G. Morgan <>.

Linux-PAM Manual                  09/19/2013                     PAM_FILTER(8)
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