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4.1 Configuration file syntax

The reader should note that the Linux-PAM specific tokens in this file are case insensitive. The module paths, however, are case sensitive since they indicate a file's name and reflect the case dependence of typical Linux file-systems. The case-sensitivity of the arguments to any given module is defined for each module in turn.

In addition to the lines described below, there are two special characters provided for the convenience of the system administrator: comments are preceded by a `#' and extend to the next end-of-line; also, module specification lines may be extended with a `\' escaped newline.

A general configuration line of the /etc/pam.conf file has the following form:

service-name   module-type   control-flag   module-path   arguments
Below, we explain the meaning of each of these tokens. The second (and more recently adopted) way of configuring Linux-PAM is via the contents of the /etc/pam.d/ directory. Once we have explained the meaning of the above tokens, we will describe this method.

service-name

The name of the service associated with this entry. Frequently the service name is the conventional name of the given application. For example, `ftpd', `rlogind' and `su', etc. .

There is a special service-name, reserved for defining a default authentication mechanism. It has the name `OTHER' and may be specified in either lower or upper case characters. Note, when there is a module specified for a named service, the `OTHER' entries are ignored.

module-type

One of (currently) four types of module. The four types are as follows:

control-flag

One of (currently) four tokens that indicate the severity of concern associated with the success or failure of a given module. Linux-PAM provides for the stacking of similar modules, providing a method of sequentially exposing the user to more than one authentication mechanism per service application. The application is not made aware of the individual success or failure of modules listed in the `/etc/pam.conf' file. Instead, it receives a summary success or fail response from the Linux-PAM library. The order of execution of these modules is that of the entries in the /etc/pam.conf file; earlier entries are executed before later ones.

The policy for determining this response is based on these three control-flags:

module-path

The path-name of the dynamically loadable object file; the pluggable module itself. If the first character of the module path is `/', it is assumed to be a complete path. If this is not the case, the given module path is appended to the default module path: /usr/lib/security (but see the notes above).

args

The args are a list of tokens that are passed to the module when it is invoked. Much like arguments to a typical Linux shell command. Generally, valid arguments are optional and are specific to any given module. Invalid arguments are ignored by a module, however, when encountering an invalid argument, the module is required to write an error to syslog(3). For a list of generic options see the next section.

Any line, in /etc/pam.conf, that is not formatted correctly is ignored by Linux-PAM; however, a corresponding error is written to the system log files with a call to syslog(3).


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