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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.

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 Upon return the handle pamh is no longer valid and all memory associated with it will be invalid.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.

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.

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.

The pam_chauthtok(3) function is used to change the authentication token for a given user on request or because the token has expired.

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).

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.

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.

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.

05/07/2023 Linux-PAM