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Manual Pages  — PAM_CONV


pam_conv – PAM conversation system



Pluggable Authentication Module Library (libpam, -lpam)


#include <security/pam_appl.h>
struct pam_message {
        int      msg_style;
        char    *msg;

struct pam_response {         char *resp;         int resp_retcode; };

struct pam_conv {         int (*conv)(int, const struct pam_message **,          struct pam_response **, void *);         void *appdata_ptr; };


The PAM library uses an application-defined callback to communicate with the user. This callback is specified by the struct pam_conv passed to pam_start() at the start of the transaction. It is also possible to set or change the conversation function at any point during a PAM transaction by changing the value of the PAM_CONV item.

The conversation function's first argument specifies the number of messages (up to PAM_MAX_NUM_MSG) to process. The second argument is a pointer to an array of pointers to pam_message structures containing the actual messages.

Each message can have one of four types, specified by the msg_style member of struct pam_message:
  Display a prompt and accept the user's response without echoing it to the terminal. This is commonly used for passwords.
  Display a prompt and accept the user's response, echoing it to the terminal. This is commonly used for login names and one-time passphrases.
  Display an error message.
  Display an informational message.

In each case, the prompt or message to display is pointed to by the msg member of struct pam_message. It can be up to PAM_MAX_MSG_SIZE characters long, including the terminating NUL.

On success, the conversation function should allocate and fill a contiguous array of struct pam_response, one for each message that was passed in. A pointer to the user's response to each message (or NULL in the case of informational or error messages) should be stored in the resp member of the corresponding struct pam_response. Each response can be up to PAM_MAX_RESP_SIZE characters long, including the terminating NUL.

The resp_retcode member of struct pam_response is unused and should be set to zero.

The conversation function should store a pointer to this array in the location pointed to by its third argument. It is the caller's responsibility to release both this array and the responses themselves, using free(3). It is the conversation function's responsibility to ensure that it is legal to do so.

The appdata_ptr member of struct pam_conv is passed unmodified to the conversation function as its fourth and final argument.

On failure, the conversation function should release any resources it has allocated, and return one of the predefined PAM error codes.


The conversation function should return one of the following values:
  Memory buffer error.
  Conversation failure.
  System error.


openpam_nullconv(3), openpam_ttyconv(3), pam(3), pam_error(3), pam_get_item(3), pam_info(3), pam_prompt(3), pam_set_item(3), pam_start(3)


X/Open Single Sign-On Service (XSSO) - Pluggable Authentication Modules, June 1997.


The OpenPAM library and this manual page were developed for the FreeBSD Project by ThinkSec AS and Network Associates Laboratories, the Security Research Division of Network Associates, Inc. under DARPA/SPAWAR contract N66001-01-C-8035 ("CBOSS"), as part of the DARPA CHATS research program.

The OpenPAM library is maintained by Dag-Erling Sm/orgrav <Mt des@des.no>.

PAM_CONV (3) April 30, 2017

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