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NAME | SYNOPSIS | DESCRIPTION | SEE ALSO | COLOPHON |
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PAM_CAP(8) System Manager's Manual PAM_CAP(8)
pam_cap - Capabilities PAM module
[service-name] auth control-flag pam_cap [options]
The pam_so module can be used to specify Inheritable capabilities
to process trees rooted in the PAM application. The module also
supports blocking Bounding vector capabilities and adding Ambient
vector capabilities.
For general PAM apps to work correctly, the application must be
run with at least CAP_SETPCAP raised in its Permitted capability
flag. Many PAM applications run as root, which has all of the bits
in the Bounding set raised, so this requirement is typically met.
To grant an Ambient vector capability, the corresponding Permitted
bit must be available to the application too.
The pam_so module is a Linux-PAM auth module. It provides
functionality to back pam_sm_authenticate() and pam_sm_setcred().
It is the latter that actually modifies the inheritable 3-tuple of
capability vectors: the configured IAB. In a typical application
configuration you might have a line like this:
auth optional pam_cap.so
The module arguments are:
○ debug: While supported, this is a no-op at present.
○ config=/path/to/file: Override the default config for the
module. The unspecified default value for this file is
/etc/security/capability.conf. Note, config=/dev/null is a
valid value. See default= below for situations in which this
might be appropriate.
○ keepcaps: This is as much as the pam_cap.so module can do to
help an application support use of the Ambient capability
vector. The application support for the Ambient set is poor at
the present time.
○ autoauth: This argument causes the pam_cap.so module to return
PAM_SUCCESS if the PAM_USER being authenticated exists. The
absence of this argument will cause pam_cap.so to only return
PAM_SUCCESS if the PAM_USER is covered by a specific rule in
the prevailing config file.
○ default=IAB: This argument is ignored if the prevailing
configuration file contains a "*" rule. If there is no such
rule, the IAB 3-tuple is inserted at the end of the config
file and applies to all PAM_USERs not covered by an earlier
rule. Note, if you want all PAM_USERs to be covered by this
default rule, you can supply the module argument
config=/dev/null.
○ defer: This argument arranges for the IAB capabilities granted
to a user to be added sufficiently late in the Linux-PAM
authentication stack that they stick. That is, after the
application does its setuid(UID) call. As such, in conjunction
with the keepcaps module argument, such compliant applications
can support granting Ambient vector capabilities with
pam_cap.so.
pam.conf(5), capability.conf(5), cap_text_formats(7), pam(8).
This page is part of the libcap (capabilities commands and
library) project. Information about the project can be found at
⟨https://git.kernel.org/pub/scm/libs/libcap/libcap.git/⟩. If you
have a bug report for this manual page, send it to
morgan@kernel.org (please put "libcap" in the Subject line). This
page was obtained from the project's upstream Git repository
⟨https://git.kernel.org/pub/scm/libs/libcap/libcap.git/⟩ on
2025-08-11. (At that time, the date of the most recent commit
that was found in the repository was 2025-08-10.) 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 man-pages@man7.org
2025-03-19 PAM_CAP(8)
Pages that refer to this page: capability.conf(5), cap_text_formats(7)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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