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NAME | DESCRIPTION | FILES | ERRORS | CONFORMING TO | SEE ALSO | COLOPHON |
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PAM(8) Linux-PAM Manual PAM(8)
PAM, pam - Pluggable Authentication Modules for Linux
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 configuration 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.
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.
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 perform the actual
authentication tasks.
Linux-PAM separates the tasks of authentication into four
independent management groups: account management; authentication
management; password management; and session management. (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 - authenticate a user and set up user credentials.
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 hardware 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 authentication 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.
/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.
Typically errors generated by the Linux-PAM system of libraries,
will be written to syslog(3).
DCE-RFC 86.0, October 1995. Contains additional features, but
remains backwardly compatible with this RFC.
pam(3), pam_authenticate(3), pam_sm_setcred(3), pam_strerror(3),
PAM(8)
This page is part of the linux-pam (Pluggable Authentication
Modules for Linux) project. Information about the project can be
found at ⟨http://www.linux-pam.org/⟩. If you have a bug report
for this manual page, see ⟨//www.linux-pam.org/⟩. This page was
obtained from the project's upstream Git repository
⟨https://github.com/linux-pam/linux-pam.git⟩ on 2023-12-22. (At
that time, the date of the most recent commit that was found in
the repository was 2023-12-18.) 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
[email protected]
Linux-PAM Manual 12/22/2023 PAM(8)
Pages that refer to this page: runuser(1), su(1), misc_conv(3), pam_acct_mgmt(3), pam_authenticate(3), pam_chauthtok(3), pam_conv(3), pam_error(3), pam_get_authtok(3), pam_getenv(3), pam_getenvlist(3), pam_info(3), pam_misc_drop_env(3), pam_misc_paste_env(3), pam_misc_setenv(3), pam_prompt(3), pam_putenv(3), pam_sm_acct_mgmt(3), pam_sm_authenticate(3), pam_sm_chauthtok(3), pam_sm_close_session(3), pam_sm_open_session(3), pam_sm_setcred(3), pam_strerror(3), pam_syslog(3), access.conf(5), [email protected](5), default_contexts(5), faillock.conf(5), failsafe_context(5), group.conf(5), limits.conf(5), login.defs(5), namespace.conf(5), pam.conf(5), pam_env.conf(5), pwhistory.conf(5), selinux_config(5), sepermit.conf(5), service_seusers(5), seusers(5), systemd.exec(5), time.conf(5), user_contexts(5), [email protected](5), environ(7), cron(8), faillock(8), PAM(8), pam_access(8), pam_cap(8), pam_debug(8), pam_deny(8), pam_echo(8), pam_env(8), pam_exec(8), pam_faildelay(8), pam_faillock(8), pam_filter(8), pam_ftp(8), pam_group(8), pam_issue(8), pam_keyinit(8), pam_lastlog2(8), pam_lastlog(8), pam_limits(8), pam_listfile(8), pam_localuser(8), pam_loginuid(8), pam_mail(8), pam_mkhomedir(8), pam_motd(8), pam_namespace(8), pam_nologin(8), pam_permit(8), pam_pwhistory(8), pam_rhosts(8), pam_rootok(8), pam_securetty(8), pam_selinux(8), pam_sepermit(8), pam_setquota(8), pam_shells(8), pam_stress(8), pam_succeed_if(8), pam_systemd(8), pam_systemd_home(8), pam_time(8), pam_timestamp(8), pam_timestamp_check(8), pam_tty_audit(8), pam_umask(8), pam_unix(8), pam_userdb(8), pam_usertype(8), pam_warn(8), pam_wheel(8), pam_xauth(8)
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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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