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) 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         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 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.

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 2020-09-18.  If you discover
       any rendering problems in this HTML version of the page, or you
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       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail

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