'\" t
.\"     Title: pam
.\"    Author: [FIXME: author] [see http://docbook.sf.net/el/author]
.\" Generator: DocBook XSL Stylesheets v1.79.1 <http://docbook.sf.net/>
.\"      Date: 09/03/2021
.\"    Manual: Linux-PAM Manual
.\"    Source: Linux-PAM Manual
.\"  Language: English
.\"
.TH "PAM" "3" "09/03/2021" "Linux-PAM Manual" "Linux-PAM Manual"
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.SH "NAME"
pam \- Pluggable Authentication Modules Library
.SH "SYNOPSIS"
.sp
.ft B
.nf
#include <security/pam_appl\&.h>
.fi
.ft
.sp
.ft B
.nf
#include <security/pam_modules\&.h>
.fi
.ft
.sp
.ft B
.nf
#include <security/pam_ext\&.h>
.fi
.ft
.SH "DESCRIPTION"
.PP
\fBPAM\fR
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
\fBlogin\fR(1)
and
\fBsu\fR(1)) defer to to perform standard authentication tasks\&.
.SS "Initialization and Cleanup"
.PP
The
\fBpam_start\fR(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\&.
.PP
The
\fBpam_end\fR(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 Upon return the handle pamh is no longer valid and all memory associated with it will be invalid\&.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\&.
.SS "Authentication"
.PP
The
\fBpam_authenticate\fR(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\&.
.PP
The
\fBpam_setcred\fR(3)
function manages the user\*(Aqs credentials\&.
.SS "Account Management"
.PP
The
\fBpam_acct_mgmt\fR(3)
function is used to determine if the user\*(Aqs 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\&.
.SS "Password Management"
.PP
The
\fBpam_chauthtok\fR(3)
function is used to change the authentication token for a given user on request or because the token has expired\&.
.SS "Session Management"
.PP
The
\fBpam_open_session\fR(3)
function sets up a user session for a previously successful authenticated user\&. The session should later be terminated with a call to
\fBpam_close_session\fR(3)\&.
.SS "Conversation"
.PP
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
\fIstruct pam_conv\fR
passed to
\fBpam_start\fR(3)
at the start of the transaction\&. See
\fBpam_conv\fR(3)
for details\&.
.SS "Data Objects"
.PP
The
\fBpam_set_item\fR(3)
and
\fBpam_get_item\fR(3)
functions allows applications and PAM service modules to set and retrieve PAM information\&.
.PP
The
\fBpam_get_user\fR(3)
function is the preferred method to obtain the username\&.
.PP
The
\fBpam_set_data\fR(3)
and
\fBpam_get_data\fR(3)
functions allows PAM service modules to set and retrieve free\-form data from one invocation to another\&.
.SS "Environment and Error Management"
.PP
The
\fBpam_putenv\fR(3),
\fBpam_getenv\fR(3)
and
\fBpam_getenvlist\fR(3)
functions are for maintaining a set of private environment variables\&.
.PP
The
\fBpam_strerror\fR(3)
function returns a pointer to a string describing the given PAM error code\&.
.SH "RETURN VALUES"
.PP
The following return codes are known by PAM:
.PP
PAM_ABORT
.RS 4
Critical error, immediate abort\&.
.RE
.PP
PAM_ACCT_EXPIRED
.RS 4
User account has expired\&.
.RE
.PP
PAM_AUTHINFO_UNAVAIL
.RS 4
Authentication service cannot retrieve authentication info\&.
.RE
.PP
PAM_AUTHTOK_DISABLE_AGING
.RS 4
Authentication token aging disabled\&.
.RE
.PP
PAM_AUTHTOK_ERR
.RS 4
Authentication token manipulation error\&.
.RE
.PP
PAM_AUTHTOK_EXPIRED
.RS 4
Authentication token expired\&.
.RE
.PP
PAM_AUTHTOK_LOCK_BUSY
.RS 4
Authentication token lock busy\&.
.RE
.PP
PAM_AUTHTOK_RECOVERY_ERR
.RS 4
Authentication information cannot be recovered\&.
.RE
.PP
PAM_AUTH_ERR
.RS 4
Authentication failure\&.
.RE
.PP
PAM_BUF_ERR
.RS 4
Memory buffer error\&.
.RE
.PP
PAM_CONV_ERR
.RS 4
Conversation failure\&.
.RE
.PP
PAM_CRED_ERR
.RS 4
Failure setting user credentials\&.
.RE
.PP
PAM_CRED_EXPIRED
.RS 4
User credentials expired\&.
.RE
.PP
PAM_CRED_INSUFFICIENT
.RS 4
Insufficient credentials to access authentication data\&.
.RE
.PP
PAM_CRED_UNAVAIL
.RS 4
Authentication service cannot retrieve user credentials\&.
.RE
.PP
PAM_IGNORE
.RS 4
The return value should be ignored by PAM dispatch\&.
.RE
.PP
PAM_MAXTRIES
.RS 4
Have exhausted maximum number of retries for service\&.
.RE
.PP
PAM_MODULE_UNKNOWN
.RS 4
Module is unknown\&.
.RE
.PP
PAM_NEW_AUTHTOK_REQD
.RS 4
Authentication token is no longer valid; new one required\&.
.RE
.PP
PAM_NO_MODULE_DATA
.RS 4
No module specific data is present\&.
.RE
.PP
PAM_OPEN_ERR
.RS 4
Failed to load module\&.
.RE
.PP
PAM_PERM_DENIED
.RS 4
Permission denied\&.
.RE
.PP
PAM_SERVICE_ERR
.RS 4
Error in service module\&.
.RE
.PP
PAM_SESSION_ERR
.RS 4
Cannot make/remove an entry for the specified session\&.
.RE
.PP
PAM_SUCCESS
.RS 4
Success\&.
.RE
.PP
PAM_SYMBOL_ERR
.RS 4
Symbol not found\&.
.RE
.PP
PAM_SYSTEM_ERR
.RS 4
System error\&.
.RE
.PP
PAM_TRY_AGAIN
.RS 4
Failed preliminary check by password service\&.
.RE
.PP
PAM_USER_UNKNOWN
.RS 4
User not known to the underlying authentication module\&.
.RE
.SH "SEE ALSO"
.PP
\fBpam_acct_mgmt\fR(3),
\fBpam_authenticate\fR(3),
\fBpam_chauthtok\fR(3),
\fBpam_close_session\fR(3),
\fBpam_conv\fR(3),
\fBpam_end\fR(3),
\fBpam_get_data\fR(3),
\fBpam_getenv\fR(3),
\fBpam_getenvlist\fR(3),
\fBpam_get_item\fR(3),
\fBpam_get_user\fR(3),
\fBpam_open_session\fR(3),
\fBpam_putenv\fR(3),
\fBpam_set_data\fR(3),
\fBpam_set_item\fR(3),
\fBpam_setcred\fR(3),
\fBpam_start\fR(3),
\fBpam_strerror\fR(3)
.SH "NOTES"
.PP
The
\fIlibpam\fR
interfaces are only thread\-safe if each thread within the multithreaded application uses its own PAM handle\&.