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
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
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.
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
This page is part of the linux-pam (Pluggable Authentication
Modules for Linux) project. Information about the project can be
found at ⟨http://www.linux-pam.org/⟩. If you have a bug report
for this manual page, see ⟨//www.linux-pam.org/⟩. This page was
obtained from the tarball Linux-PAM-1.3.0.tar.bz2 fetched from
⟨http://www.linux-pam.org/library/⟩ 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 email@example.com
Linux-PAM Manual 04/01/2016 PAM_FILTER(8)