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OpenDarwin 7.2.1 - man page for pam (opendarwin section 8)

PAM(8)					 Linux-PAM Manual				   PAM(8)

NAME
       Linux-PAM - Pluggable Authentication Modules for Linux

SYNOPSIS
       /etc/pam.conf

DESCRIPTION
       This  manual is intended to offer a quick introduction to Linux-PAM.  For more information
       the reader is directed to the Linux-PAM system administrators' guide.

       Linux-PAM Is a system of libraries that handle the authentication  tasks  of  applications
       (services)  on  the  system.  The library provides a stable general interface (Application
       Programming Interface - API) that privilege granting programs (such as login(1) and su(1))
       defer to to perform standard authentication tasks.

       The  principal  feature	of  the  PAM approach is that the nature of the authentication is
       dynamically configurable.  In other words, the system administrator is free to choose  how
       individual service-providing applications will authenticate users. This dynamic configura-
       tion is set by the contents of the  single  Linux-PAM  configuration  file  /etc/pam.conf.
       Alternatively,  the  configuration can be set by individual configuration files located in
       the /etc/pam.d/ directory.  The presence of this directory will cause Linux-PAM to  ignore
       /etc/pam.conf.

       From  the  point of view of the system administrator, for whom this manual is provided, it
       is not of primary importance to understand the internal behavior of the Linux-PAM library.
       The  important  point to recognize is that the configuration file(s) define the connection
       between applications (services) and the pluggable authentication modules (PAMs) that  per-
       form the actual authentication tasks.

       Linux-PAM  separates  the tasks of authentication into four independent management groups:
       account management; authentication management; password management;  and  session  manage-
       ment.  (We highlight the abbreviations used for these groups in the configuration file.)

       Simply  put, these groups take care of different aspects of a typical user's request for a
       restricted service:

       account - provide account verification types of service: has the user's password expired?;
       is this user permitted access to the requested service?

       authentication  -  establish  the user is who they claim to be. Typically this is via some
       challenge-response request that the user must satisfy: if you are  who  you  claim  to  be
       please  enter  your password.  Not all authentications are of this type, there exist hard-
       ware based authentication schemes (such as the use of smart-cards and biometric	devices),
       with suitable modules, these may be substituted seamlessly for more standard approaches to
       authentication - such is the flexibility of Linux-PAM.

       password - this group's responsibility is the task of updating authentication  mechanisms.
       Typically, such services are strongly coupled to those of the auth group. Some authentica-
       tion mechanisms lend themselves well to being updated with such a function. Standard  UN*X
       password-based access is the obvious example: please enter a replacement password.

       session	-  this  group of tasks cover things that should be done prior to a service being
       given and after it is withdrawn. Such tasks include the maintenance of  audit  trails  and
       the mounting of the user's home directory. The session management group is important as it
       provides both an opening and closing hook for modules to affect the services available  to
       a user.

The configuration file(s)
       When a Linux-PAM aware privilege granting application is started, it activates its attach-
       ment 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.

       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 Linux-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;  auth;  password;  and  session.	 The  meaning of each of these tokens was
       explained above.

       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: requisite - failure of such a
       PAM results in the immediate termination of the authentication process; 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; sufficient - suc-
       cess 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);
       optional  - the success or failure of this module is only important if it is the only mod-
       ule in the stack associated with this service+type.

       For the more complicated syntax valid control values have the following form:

       [value1=action1value2=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; sym-
       bol_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;   auth-
       tok_recover_err; authtok_lock_busy; authtok_disable_aging; try_again; ignore; abort; auth-
       tok_expired; module_unknown; bad_item; 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, J,  signify-
       ing an action of 'jump over the next J modules in the stack'; or 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.
       die - equivalent to bad with the side effect of terminating the module stack and PAM imme-
       diately 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 imme-
       diately returning to the application.
       reset  -  clear	all memory of the state of the module stack and start again with the next
       stacked module.

       module-path - this 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/.

       module-arguments - these 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 indi-
       vidual module.

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.
       /lib/libpam.so.X - the dynamic library
       /lib/security/*.so - the PAMs

ERRORS
       Typically  errors  generated by the Linux-PAM system of libraries, will be written to sys-
       log(3).

CONFORMING TO
       DCE-RFC 86.0, October 1995.
       Contains additional features, but remains backwardly compatible with this RFC.

BUGS
       None known.

SEE ALSO
       The three Linux-PAM Guides, for system administrators, module developers, and  application
       developers.

Linux-PAM 0.74				   2001 Jan 20					   PAM(8)


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