NAME

       pam.conf, pam.d - PAM configuration files

DESCRIPTION

       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 and preferably, the
       configuration can be set by individual configuration files located in a 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:

       account
           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.

       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 ...]

       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
       take one of the following forms:

       ignore
           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']

       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 words:

               [..[..\]..]    -->   ..[..]..

       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 pam.d directories. In this case the directories are 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.

       Vendor-supplied PAM configuration files might be installed in the system directory
       /usr/lib/pam.d/ or a configurable vendor specific directory instead of the machine
       configuration directory /etc/pam.d/. If no machine configuration file is found, the
       vendor-supplied file is used. All files in /etc/pam.d/ override files with the same name
       in other directories.

       The syntax of each file in 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 service.

FILES

       /etc/pam.conf
           the configuration file

       /etc/pam.d
           the Linux-PAM configuration directory. Generally, if this directory is present, the
           /etc/pam.conf file is ignored.

       /usr/lib/pam.d
           the Linux-PAM vendor configuration directory. Files in /etc/pam.d override files with
           the same name in this directory.

SEE ALSO

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