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           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
           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
           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:
               this 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.
               this module type provides two aspects of authenticating the user.
               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:
               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.
               like required, however, in the case that such a module returns a
               failure, control is directly returned to the application. 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.
               success of such a module is enough to satisfy the authentication
               requirements of the stack of modules (if a prior required module
               has failed the success of this one is ignored). A failure of this
               module is not deemed as fatal to satisfying the application that
               this type has succeeded. If the module succeeds the PAM framework
               returns success to the application immediately without trying any
               other modules.
               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 all lines of given type from the configuration file
               specified as an argument to this control.
                     [value1=action1 value2=action2 ...]
           Where valueN corresponds to the return code from the function invoked
           in the module for which the line is defined. It is selected from one of
           these: success, open_err, symbol_err, service_err, system_err, buf_err,
           perm_denied, auth_err, cred_insufficient, authinfo_unavail,
           user_unknown, maxtries, new_authtok_reqd, acct_expired, session_err,
           cred_unavail, cred_expired, cred_err, no_module_data, conv_err,
           authtok_err, authtok_recover_err, authtok_lock_busy,
           authtok_disable_aging, try_again, ignore, abort, authtok_expired,
           module_unknown, bad_item, conv_again, incomplete, and default.
           The last of these, default, implies ?all valueN?s not mentioned
           explicitly. Note, the full list of PAM errors is available in
           /usr/include/security/_pam_types.h. The actionN can be: an unsigned
           integer, n, signifying an action of ?jump over the next n modules in
           the stack?; or take one of the following forms:
               when used with a stack of modules, the module?s return status will
               not contribute to the return code the application obtains.
               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.
               equivalent to bad with the side effect of terminating the module
               stack and PAM immediately returning to the application.
               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.
               equivalent to ok with the side effect of terminating the module
               stack and PAM immediately returning to the application.
               clear all memory of the state of the module stack and start again
               with the next stacked module.
           Each of the four keywords: required; requisite; sufficient; and
           optional, have an equivalent expression in terms of the [...] syntax.
           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
                   squid auth required user=passwd_query passwd=mada \
                         db=eminence [query=select user_name from internet_service \
                         where user_name=?%u? and password=PASSWORD(?%p?) and \
           When using this convention, you can include '[? characters inside the
           string, and if you wish to include a ']? character inside the string
           that will survive the argument parsing, you should use '\]?. In other
                   [..[..\]..]    -->   ..[..]..
           Any line in (one of) the configuration file(s), that is not formatted
           correctly, will generally tend (erring on the side of caution) to make
           the authentication process fail. A corresponding error is written to
           the system log files with a call to syslog(3).
           More flexible than the single configuration file is it to configure
           libpam via the contents of the /etc/pam.d/ directory. In this case the
           directory is filled with files each of which has a filename equal to a
           service-name (in lower-case): it is the personal configuration file for
           the named service.
           The syntax of each file in /etc/pam.d/ is similar to that of the
           /etc/pam.conf file and is made up of lines of the following form:
               type  control  module-path  module-arguments
           The only difference being that the service-name is not present. The
           service-name is of course the name of the given configuration file. For
           example, /etc/pam.d/login contains the configuration for the login


           pam(3), PAM(8), pam_start(3)

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