pam_filter(8) — Linux manual page


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

NAME         top

       pam_filter - PAM filter module

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

DESCRIPTION         top

       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)

       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         top

           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 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

           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).

           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

RETURN VALUES         top

           The new filter was set successfully.

           Critical error, immediate abort.

EXAMPLES         top

       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

SEE ALSO         top

       pam.conf(5), pam.d(5), pam(8)

AUTHOR         top

       pam_filter was written by Andrew G. Morgan <>.

COLOPHON         top

       This page is part of the linux-pam (Pluggable Authentication
       Modules for Linux) project.  Information about the project can be
       found at ⟨⟩.  If you have a bug report
       for this manual page, see ⟨//⟩.  This page was
       obtained from the tarball Linux-PAM-1.3.0.tar.bz2 fetched from
       ⟨⟩ on 2021-08-27.  If you
       discover any rendering problems in this HTML version of the page,
       or you believe there is a better or more up-to-date source for
       the page, or you have corrections or improvements to the
       information in this COLOPHON (which is not part of the original
       manual page), send a mail to

Linux-PAM Manual               04/01/2016                  PAM_FILTER(8)