NAME
pam.conf, pam.d - PAM configuration filesDESCRIPTION
When a PAM aware privilege granting application is started, it activates its attachment to the PAM-API. This activation performs a number of tasks, the most important being the reading of the configuration file(s): /etc/pam.conf. Alternatively, this may be the contents of the /etc/pam.d/ directory. The presence of this directory will cause Linux-PAM to ignore /etc/pam.conf. These files list the PAMs that will do the authentication tasks required by this service, and the appropriate behavior of the PAM-API in the event that individual PAMs fail. The syntax of the /etc/pam.conf configuration file is as follows. The file is made up of a list of rules, each rule is typically placed on a single line, but may be extended with an escaped end of line: `\<LF>'. Comments are preceded with `#' marks and extend to the next end of line. The format of each rule is a space separated collection of tokens, the first three being case-insensitive: service type control module-path module-arguments The syntax of files contained in the /etc/pam.d/ directory, are identical except for the absence of any service field. In this case, the service is the name of the file in the /etc/pam.d/ directory. This filename must be in lower case. An important feature of PAM, is that a number of rules may be stacked to combine the services of a number of PAMs for a given authentication task. The service is typically the familiar name of the corresponding application: login and su are good examples. The service-name, other, is reserved for giving default rules. Only lines that mention the current service (or in the absence of such, the other entries) will be associated with the given service-application. The type is the management group that the rule corresponds to. It is used to specify which of the management groups the subsequent module is to be associated with. Valid entries are: accountthis module type performs non-authentication
based account management. It is typically used to restrict/permit access to a
service based on the time of day, currently available system resources
(maximum number of users) or perhaps the location of the applicant user --
'root' login only on the console.
auth
this module type provides two aspects of
authenticating the user. Firstly, it establishes that the user is who they
claim to be, by instructing the application to prompt the user for a password
or other means of identification. Secondly, the module can grant group
membership or other privileges through its credential granting
properties.
password
this module type is required for updating the
authentication token associated with the user. Typically, there is one module
for each 'challenge/response' based authentication (auth) type.
session
this module type is associated with doing
things that need to be done for the user before/after they can be given
service. Such things include the logging of information concerning the
opening/closing of some data exchange with a user, mounting directories,
etc.
If the type value from the list above is prepended with a -
character the PAM library will not log to the system log if it is not possible
to load the module because it is missing in the system. This can be useful
especially for modules which are not always installed on the system and are
not required for correct authentication and authorization of the login
session.
The third field, control, indicates the behavior of the PAM-API should
the module fail to succeed in its authentication task. There are two types of
syntax for this control field: the simple one has a single simple keyword; the
more complicated one involves a square-bracketed selection of
value=action pairs.
For the simple (historical) syntax valid control values are:
required
failure of such a PAM will ultimately lead to
the PAM-API returning failure but only after the remaining stacked
modules (for this service and type) have been invoked.
requisite
like required, however, in the case
that such a module returns a failure, control is directly returned to the
application or to the superior PAM stack. The return value is that associated
with the first required or requisite module to fail. Note, this flag can be
used to protect against the possibility of a user getting the opportunity to
enter a password over an unsafe medium. It is conceivable that such behavior
might inform an attacker of valid accounts on a system. This possibility
should be weighed against the not insignificant concerns of exposing a
sensitive password in a hostile environment.
sufficient
if such a module succeeds and no prior
required module has failed the PAM framework returns success to the
application or to the superior PAM stack immediately without calling any
further modules in the stack. A failure of a sufficient module is
ignored and processing of the PAM module stack continues unaffected.
optional
the success or failure of this module is only
important if it is the only module in the stack associated with this
service+ type.
include
include all lines of given type from the
configuration file specified as an argument to this control.
substack
include all lines of given type from the
configuration file specified as an argument to this control. This differs from
include in that evaluation of the done and die actions in
a substack does not cause skipping the rest of the complete module stack, but
only of the substack. Jumps in a substack also can not make evaluation jump
out of it, and the whole substack is counted as one module when the jump is
done in a parent stack. The reset action will reset the state of a
module stack to the state it was in as of beginning of the substack
evaluation.
For the more complicated syntax valid control values have the following
form:
[value1=action1 value2=action2 ...]
when used with a stack of modules, the
module's return status will not contribute to the return code the application
obtains.
bad
this action indicates that the return code
should be thought of as indicative of the module failing. If this module is
the first in the stack to fail, its status value will be used for that of the
whole stack. This is the default action for all return codes.
die
equivalent to bad with the side effect
of terminating the module stack and PAM immediately returning to the
application.
ok
this tells PAM that the administrator thinks
this return code should contribute directly to the return code of the full
stack of modules. In other words, if the former state of the stack would lead
to a return of PAM_SUCCESS, the module's return code will override this
value. Note, if the former state of the stack holds some value that is
indicative of a modules failure, this 'ok' value will not be used to override
that value.
done
equivalent to ok with the side effect
of terminating the module stack and PAM immediately returning to the
application unless there was a non-ignored module failure before.
N (an unsigned integer)
jump over the next N modules in the stack.
Note that N equal to 0 is not allowed, it would be treated as ignore in
such case. The side effect depends on the PAM function call: for
pam_authenticate, pam_acct_mgmt, pam_chauthtok, and
pam_open_session it is ignore; for pam_setcred and
pam_close_session it is one of ignore, ok, or bad
depending on the module's return value.
reset
clear all memory of the state of the module
stack and start again with the next stacked module.
If a return code's action is not specifically defined via a valueN token,
and the default value is not specified, that return code's action
defaults to bad.
Each of the four keywords: required; requisite; sufficient; and optional, have
an equivalent expression in terms of the [...] syntax. They are as follows:
required
[success=ok new_authtok_reqd=ok ignore=ignore
default=bad]
requisite
[success=ok new_authtok_reqd=ok ignore=ignore
default=die]
sufficient
[success=done new_authtok_reqd=done
default=ignore]
optional
[success=ok new_authtok_reqd=ok
default=ignore]
module-path is either the full filename of the PAM to be used by the
application (it begins with a '/'), or a relative pathname from the default
module location: /lib/security/ or /lib64/security/, depending on the
architecture.
module-arguments are a space separated list of tokens that can be used to
modify the specific behavior of the given PAM. Such arguments will be
documented for each individual module. Note, if you wish to include spaces in
an argument, you should surround that argument with square brackets.
squid auth required pam_mysql.so user=passwd_query passwd=mada \ db=eminence [query=select user_name from internet_service \ where user_name='%u' and password=PASSWORD('%p') and \ service='web_proxy']
[..[..\]..] --> ..[..]..
type control module-path module-arguments
SEE ALSO
pam(3), PAM(8), pam_start(3)09/03/2021 | Linux-PAM Manual |