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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUES | SEE ALSO | NOTES | COLOPHON |
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PAM(3) Linux-PAM Manual PAM(3)
pam - Pluggable Authentication Modules Library
#include <security/pam_appl.h>
#include <security/pam_modules.h>
#include <security/pam_ext.h>
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.
Initialization and Cleanup
The pam_start(3) function creates the PAM context and initiates
the PAM transaction. It is the first of the PAM functions that
needs to be called by an application. The transaction state is
contained entirely within the structure identified by this handle,
so it is possible to have multiple transactions in parallel. But
it is not possible to use the same handle for different
transactions, a new one is needed for every new context.
The pam_end(3) function terminates the PAM transaction and is the
last function an application should call in the PAM context. Upon
return the handle pamh is no longer valid and all memory
associated with it will be invalid. It can be called at any time
to terminate a PAM transaction.
Authentication
The pam_authenticate(3) function is used to authenticate the user.
The user is required to provide an authentication token depending
upon the authentication service, usually this is a password, but
could also be a finger print.
The pam_setcred(3) function manages the user's credentials.
Account Management
The pam_acct_mgmt(3) function is used to determine if the user's
account is valid. It checks for authentication token and account
expiration and verifies access restrictions. It is typically
called after the user has been authenticated.
Password Management
The pam_chauthtok(3) function is used to change the authentication
token for a given user on request or because the token has
expired.
Session Management
The pam_open_session(3) function sets up a user session for a
previously successful authenticated user. The session should later
be terminated with a call to pam_close_session(3).
Conversation
The PAM library uses an application-defined callback to allow a
direct communication between a loaded module and the application.
This callback is specified by the struct pam_conv passed to
pam_start(3) at the start of the transaction. See pam_conv(3) for
details.
Data Objects
The pam_set_item(3) and pam_get_item(3) functions allows
applications and PAM service modules to set and retrieve PAM
information.
The pam_get_user(3) function is the preferred method to obtain the
username.
The pam_set_data(3) and pam_get_data(3) functions allows PAM
service modules to set and retrieve free-form data from one
invocation to another.
Environment and Error Management
The pam_putenv(3), pam_getenv(3) and pam_getenvlist(3) functions
are for maintaining a set of private environment variables.
The pam_strerror(3) function returns a pointer to a string
describing the given PAM error code.
The following return codes are known by PAM:
PAM_ABORT
Critical error, immediate abort.
PAM_ACCT_EXPIRED
User account has expired.
PAM_AUTHINFO_UNAVAIL
Authentication service cannot retrieve authentication info.
PAM_AUTHTOK_DISABLE_AGING
Authentication token aging disabled.
PAM_AUTHTOK_ERR
Authentication token manipulation error.
PAM_AUTHTOK_EXPIRED
Authentication token expired.
PAM_AUTHTOK_LOCK_BUSY
Authentication token lock busy.
PAM_AUTHTOK_RECOVERY_ERR
Authentication information cannot be recovered.
PAM_AUTH_ERR
Authentication failure.
PAM_BUF_ERR
Memory buffer error.
PAM_CONV_ERR
Conversation failure.
PAM_CRED_ERR
Failure setting user credentials.
PAM_CRED_EXPIRED
User credentials expired.
PAM_CRED_INSUFFICIENT
Insufficient credentials to access authentication data.
PAM_CRED_UNAVAIL
Authentication service cannot retrieve user credentials.
PAM_IGNORE
The return value should be ignored by PAM dispatch.
PAM_MAXTRIES
Have exhausted maximum number of retries for service.
PAM_MODULE_UNKNOWN
Module is unknown.
PAM_NEW_AUTHTOK_REQD
Authentication token is no longer valid; new one required.
PAM_NO_MODULE_DATA
No module specific data is present.
PAM_OPEN_ERR
Failed to load module.
PAM_PERM_DENIED
Permission denied.
PAM_SERVICE_ERR
Error in service module.
PAM_SESSION_ERR
Cannot make/remove an entry for the specified session.
PAM_SUCCESS
Success.
PAM_SYMBOL_ERR
Symbol not found.
PAM_SYSTEM_ERR
System error.
PAM_TRY_AGAIN
Failed preliminary check by password service.
PAM_USER_UNKNOWN
User not known to the underlying authentication module.
pam_acct_mgmt(3), pam_authenticate(3), pam_chauthtok(3),
pam_close_session(3), pam_conv(3), pam_end(3), pam_get_data(3),
pam_getenv(3), pam_getenvlist(3), pam_get_item(3),
pam_get_user(3), pam_open_session(3), pam_putenv(3),
pam_set_data(3), pam_set_item(3), pam_setcred(3), pam_start(3),
pam_strerror(3)
The libpam interfaces are only thread-safe if each thread within
the multithreaded application uses its own PAM handle.
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
man-pages@man7.org
Linux-PAM Manual 12/22/2023 PAM(3)
Pages that refer to this page: 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.conf(5), PAM(8), pam_filter(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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