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10. Extensions

The use of extension language allows extending the functionality of GNU Radius without having to modify its source code. The two extension languages supported are Rewrite and Scheme. Use of Rewrite is always enabled. Use of Scheme requires Guile version 1.4 or higher.

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10.1 Filters

The simplest way to extend the functionality of Radius is to use filters. A filter is an external program that communicates with Radius via its standard input and output channels.

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10.1.1 Getting Acquainted with Filters

Suppose we wish to implement an authentication method based on the user name and the user's calling station ID. We have a database of user names with valid IDs, and the new method should authenticate a user only if the combination {user_name, id} is found in this database.

We write a filter program that reads its standard input line by line. Each input line must consist of exactly two words: the user name and the calling station ID. For each input line, the program prints 0 if the {user_name, id} is found in the database and 1 otherwise. Let's suppose for the sake of example that the database is a plaintext file and the filter is written in a shell programming language. Then it will look like

#! /bin/sh


while read NAME CLID
    if grep "$1:$2" $DB; then
        echo "0"
        echo "1"

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10.1.2 Declaring the Filter

Here is how this filter is declared in the ‘raddb/config’ file:

filters {
    filter check_clid {
        exec-path "/usr/libexec/myfilter";
        error-log "myfilter.log";
        auth {
            input-format "%C{User-Name}
            wait-reply yes;

Let's analyze this declaration line by line:

  1. filters {

    This keyword opens the filters declaration block. The block may contain several declarations.

  2. filter check_clid {

    This line starts the declaration of this particular filter and names it ‘check_clid’.

  3. exec-path "/usr/libexec/myfilter";

    This line tells radiusd where to find the executable image of this filter.

  4. error-log "myfilter.log";

    The diagnostic output from this filter must be redirected to the file ‘myfilter.log’ in the current logging directory

  5. auth {

    This filter will process authentication requests.

  6. input-format "%C{User-Name} %C{Calling-Station-Id}";

    Define the input line format for this filter. The %C{} expressions will be replaced by the values of the corresponding attributes from the incoming request (see section Macro Substitution).

  7. wait-reply yes;

    radiusd will wait for the reply from this filter to decide whether to authenticate the user.

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10.1.3 Invoking the Filter from a User Profile

To invoke this filter from the user profile, specify its name prefixed with ‘|’ in the value of Exec-Program-Wait attribute, like this:

DEFAULT Auth-Type = System,
                Simultaneous-Use = 1
        Exec-Program-Wait = "|check_clid"

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10.1.4 Adding Reply Attributes

Apart from simply deciding whether to authenticate a user, the filter can also modify the reply pairs.

#! /bin/sh


while read NAME CLID
    if grep "$1:$2" $DB; then
        echo "0 Service-Type = Login, Session-Timeout = 1200"
        echo "1 Reply-Message = 
              \"You are not authorized to log in\""

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10.1.5 Accounting Filters

Let's suppose we further modify our filter to also handle accounting requests. To discern between the authentication and accounting requests we'll prefix each authentication request with the word ‘auth’ and each accounting request with the word ‘acct’. Furthermore, the input line for accounting requests will contain a timestamp.

Now, our filter program will look as follows:

#! /bin/sh


    case CODE
        if grep "$1:$2" $DB; then
            echo "0 Service-Type = Login, \
                  Session-Timeout = 1200"
            echo "1 Reply-Message = \
                  \"You are not authorized to log in\""
        echo "$CODE $NAME $CLID $DATE" >> $ACCT_DB

Its declaration in the ‘raddb/config’ will also change:

filter check_clid {
    exec-path "/usr/libexec/myfilter";
    error-log "myfilter.log";
    auth {
        input-format "auth %C{User-Name} 
        wait-reply yes;
    acct {
        input-format "acct %C{User-Name} 
                      %C{Calling-Station-Id} %D";
        wait-reply no;

(The input-format lines are split for readability. Each of them is actually one line).

Notice wait-reply no in the acct statement. It tells radiusd that it shouldn't wait for the response on accounting requests from the filter.

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10.1.6 Invoking the Accounting Filter

To invoke the accounting filter, specify its name prefixed with a vertical bar character as a value of Acct-Ext-Program in our ‘raddb/hints’ file. For example:

        Acct-Ext-Program = "|check_clid:

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10.2 Rewrite

Rewrite is the GNU Radius extension language. Its name reflects the fact that it was originally designed to rewrite the broken request packets so they could be processed as usual (see section Rewriting Incoming Requests). Beside this basic use, however, Rewrite functions are used to control various aspects of GNU Radius functionality, such as verifying the activity of user sessions, controlling the amount of information displayed in log messages, etc (see section Interaction with Radius).

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10.2.1 Syntax Overview

The syntax of Rewrite resembles that of C. Rewrite has two basic data types: integer and string. It does not have global variables; all variables are automatic. The only exceptions are the A/V pairs from the incoming request, which are accessible to Rewrite functions via the special notation %[attr].

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10.2.2 Quick Start

As an example, let's consider the following Rewrite function:

foo(integer i)
    string rc;
    if (i % 2)
        rc = "odd";
        rc = "even";
    return "the number is " + rc;

The function takes an integer argument and returns the string ‘the number is odd’ or ‘the number is even’, depending on the value of i. This illustrates the fact that in Rewrite the addition operator is defined on the string type. The result of such operation is the concatenation of operands.

Another example is a function that adds a prefix to the User-Name attribute:

        %[User-Name] = "pfx-" + %[User-Name];
        return 0;

This function manipulates the contents of the incoming request; its return value has no special meaning.

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10.2.3 Interaction with Radius

A Rewrite function can be invoked in several ways, depending on its purpose. There are three major kinds of Rewrite functions:

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10.2.4 Rewriting Incoming Requests

The need for rewriting the incoming requests arises from the fact that some NASes are very particular about the information they send with the requests. There are cases when the information they send is hardly usable or even completely unusable. For example, a Cisco AS5300 terminal server used as a voice-over IP router packs a lot of information into its Acct-Session-Id attribute. Though the information stored there is otherwise relevant, it makes proper accounting impossible, since the Acct-Session-Id attributes in the start and stop packets of the same session become different, and thus Radius cannot determine the session start to which the given session stop request corresponds (see section Acct-Session-Id).

In order to cope with such NASes, GNU Radius is able to invoke a Rewrite function upon arrival of the packet and before processing it further. This function can transform the packet so that it obtains the form prescribed by RFCs and its further processing becomes possible.

For example, in the case of the AS5300 router, a corresponding Rewrite function parses the Acct-Session-Id attribute; breaks it down into fields; stores them into proper attributes, creating them if necessary; and finally replaces Acct-Session-Id with its real value, which is the same for the start and stop records corresponding to a single session. Thus all the information that came with the packet is preserved, but the packet itself is made usable for proper accounting.

A special attribute, Rewrite-Function, is used to trigger invocation of a Rewrite function. Its value is a name of the function to be invoked.

When used in a ‘naslist’ profile, the attribute causes the function to be invoked when the incoming request matches the huntgroup (see section Huntgroups). For example, to have a function fixup invoked for each packet from the NAS, the following huntgroup rule may be used:

         Rewrite-Function = "fixup"

The Rewrite-Function attribute may also be used in a ‘hints’ rule. In this case, it will invoke the function if the request matches the rule (see section Hints). For example, this ‘hints’ rule will cause the function to be invoked for each request containing the user name starting with ‘P’:

DEFAULT  Prefix = "P"
         Rewrite-Function = "fixup"

Note that in both cases the attribute can be used either in LHS or in RHS pairs of a rule.

The packet rewrite function must be declared as having no arguments and returning an integer value:

integer fixup()

The actual return value from such a function is ignored, the integer return type is just a matter of convention.

The following subsection present some examples of packet rewrite functions.

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The examples found in this chapter are working functions that can be used with various existing NAS types. They are taken from the ‘rewrite’ file contained in distribution of GNU Radius.

1. Port rewriting for MAX Ascend terminal servers

Some MAX Ascend terminal servers pack additional information into the NAS-Port-Id attribute. The port number is constructed as XYYZZ, where X = 1 for digital, X = 2 for analog, YY is the line number (1 for first PRI/T1/E1, 2 for second, and so on), and ZZ is the channel number (on the PRI or channelized T1/E1).

The following rewrite functions are intended to compute the integer port number in the range (1 .. portcnt), where portcnt represents the real number of physical ports available on the NAS. Such a port number can be used, for example, to create a dynamic pool of IP addresses (see section Framed-IP-Address).

 * decode MAX port number
 * input: P        --  The value of NAS-Port-Id attribute
 *        portcnt  --  number of physical ports on the NAS
max_decode_port(integer P, integer portcnt)
    if (P > 9999) {
        integer s, l, c;

        s = P / 10000;
        l = (P - (10000 * s))/100; 
        c = P - ((10000 * s) + (100 * l)); 
        return (c-1) + (l-1) * portcnt;
    return P;

 * Interface function for MAX terminal server with 23 ports.
 * Note that it saves the received NAS-Port-Id attribute in
 * the Orig-NAS-Port-Id attribute. The latter must be
 * defined somewhere in the dictionary
    %[Orig-NAS-Port-Id] = %[NAS-Port-Id];
                                  # Preserve original data
    %[NAS-Port-Id] = max_decode_port(%[NAS-Port-Id], 23);
    return 0;

2. Session ID parsing for Cisco AS 5300 series

Cisco VOIP IOS encodes a lot of other information into its Acct-Session-Id. The pieces of information are separated by ‘/’ characters. The part of Acct-Session-Id up to the first ‘/’ character is the actual session ID.

On the other hand, its accounting packets lack NAS-Port-Id, though they may contain the vendor-specific pair with code 2 (vendor PEC 9), which is a string in the form ‘ISDN 9:D:999’ (‘9’ represents any decimal digit). The number after the last ‘:’ character can be used as a port number.

The following code parses Acct-Session-Id attribute and stores the information it contains in various other attributes, generates a normal Acct-Session-Id, and attempts to generate a NAS-Port-Id attribute.

 * The port rewriting function for Cisco AS5300 used for
 * VoIP. This function is used to generate NAS-Port-Id pair
 * on the basis of vendor-specific pair 2. If the latter is
 * in the form "ISDN 9:D:999" (where each 9 represents a
 * decimal digit), then the function returns the number
 * after the last colon. This is used as a port number.
cisco_pid(string A)
    if (A =~ 
         [A-Z0-9][A-Z0-9]*:\([0-9][0-9]*\)") {
        return (integer)\2;
    return -1;

 * This function parses the packed session id.
 * The actual sid is the number before the first slash
 * character.  Other possibly relevant fields are also
 * parsed out and saved in the Voip-* A/V pairs. The latter
 * should be defined somewhere in the dictionary.
 * Note that the regular expression in this example
 * spans several lines for readability. It should be on one 
 * line in real file.
cisco_sid(string S)
   if (S =~ "\(.[^/]*\)/[^/]*/[^/]*/\([^/]*\)/\([^/]*\)/
             /\([^/]*\).*") {
        %[Voip-Connection-ID] = \2;
        %[Voip-Call-Leg-Type] = \3;
        %[Voip-Connection-Type] = \4;
        %[Voip-Connect-Time] = \5;
        %[Voip-Disconnect-Time] = \6;
        %[Voip-Disconnect-Cause] = \7;
        %[Voip-Remote-IP] = \8;
        return \1;
   return S;

 * Normalize cisco AS5300 packets
    integer pid;

    if ((pid = cisco_pid(%[Cisco-PRI-Circuit])) != -1) {
        if (*%[NAS-Port-Id])
            %[Orig-NAS-Port-Id] = %[NAS-Port-Id];
        %[NAS-Port-Id] = pid;
    if (*%[Acct-Session-Id]) {
        %[Orig-Acct-Session-Id] = %[Acct-Session-Id];
        %[Acct-Session-Id] = cisco_sid(%[Acct-Session-Id]);
    return 0;

3. User-name rewriting for NT machines

Users coming from Windows NT machines often authenticate themselves as ‘NT_DOMAIN\username’. The following function selects the user-name part and stores it in the User-Name attribute:

login_nt(string uname)
    integer i;
    if ((i = index(uname, '\\')) != -1)
        return substr(uname, i+1, -1);
    return uname;

    %[Orig-User-Name] = %[User-Name];
    %[User-Name] = login_nt(%[User-Name]);
    return 0;

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10.2.5 Login Verification Functions

A login verification function is invoked to process the output from the NAS. This process is described in Multiple Login Checking. The function to be invoked for given NAS is defined by a function flag in the ‘raddb/nastypes’ or ‘raddb/naslist’ file (see section NAS Types — ‘raddb/nastypes). It must be defined as follows:

Function Template: integer check (string str, string name, integer pid, string sid)

Its arguments are:


Input string. If the query method is finger, this is the string of output received from the NAS with trailing newline stripped off. If the query method is snmp, it is the received variable value converted to its string representation.


User name.


Port ID of the session.


Session ID.

The function should return non-0 if its arguments match the user's session, and 0 otherwise.

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As an example, let's consider the function for analyzing a line of output from a standard UNIX finger service. In each line of finger output the first field contains the user name; the third field, the The function must return 1 if the three fields match the input user name and port and session IDs:

check_unix(string str, string name, integer pid, string sid)
    return field(str, 1) == name
           && field(str, 3) == pid
           && field(str, 7) == sid;

The next example is a function to analyze a line of output from an SNMP query returning a user name. This function must return 1 if the entire input line matches the user name:

check_username(string str, string name, integer pid, string sid)
    return str == name;

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10.2.6 Attribute Creation Functions

These are the functions used to create Radius reply attributes. An attribute creation function can take any number of arguments. The type of its return is determined by the type of Radius attribute the value will be assigned to. To invoke the function, write its name in the A/V pair of the RHS in the ‘raddb/users’ file, e.g.:

        Service-Type = Framed-User,
            Framed-IP-Address = "=get_ip_addr("

The function get_ip_addr will be invoked after successful authentication and it will be passed the IP as its argument. An example of a useful function that can be invoked this way is

get_ip_address(integer base)
    return base + %[NAS-Port-Id] - %[NAS-Port-Id]/16;

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10.2.7 Logging Hook Functions

A logging hook functions should be declared as follows:

Function Template: string hook (integer reqtype, string nasid, integer reqid)

Type of the request. It can be converted to string using request_code_string function (see section Rewrite Built-in Functions).


NAS identifier from ‘raddb/naslist’, or its host name if not declared there


Request identifier.

Notice that the hook function shall not produce any side effects, in particular it shall not modify the incoming request in any way.

Following is an example prefix hook function that formats the incoming request data:

compat_log_prefix(integer reqtype, string nas, integer id)
        string result;

        return "(" + request_code_string(reqtype) + " "
                   + nas + " " + (string)id + " " + %[User-Name] + ")";

Here is a sample log produced by radiusd before and after enabling this function:

Auth.notice: Login OK [jsmith]
Auth.notice: (AUTHREQ nas-2 251 jsmith): Login OK [jsmith]

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10.2.8 Full Syntax Description

[ < ] [ > ]   [ << ] [ Up ] [ >> ]         [Top] [Contents] [Index] [ ? ] Rewrite Data Types

There are only two data types: integer and string, the two being coercible to each other in the sense that a string can be coerced to an integer if it contains a valid ASCII representation of a decimal, octal, or hex number, and an integer can always be coerced to a string, the result of such coercion being the ASCII string that is the decimal representation of the number.

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A symbol is a lexical token. The following symbols are recognized:

Arithmetical operators

These are ‘+’, ‘-’, ‘*’, ‘/’ representing the basic arithmetical operations, and ‘%’ meaning remainder.

Comparison operators

These are: ‘==’, ‘!=’, ‘<’, ‘<=’, ‘>’, ‘>=’ with the same meaning they have in C. Special operators are provided for regular-expression matching. The binary operator ‘=~’ returns true if its left-hand-side operand matches the regular expression on its right-hand side (see section Regular Expressions). ‘!~’ returns true if its left-hand-side operand does not match the regexp on its right-hand side. The right-hand-side operand of ‘!~’ or ‘=~’ must be a literal string, i.e., the regular expression must be known at compile time.

Unary operators

The unary operators are ‘-’ and ‘+’ for unary plus and minus, ‘!’ for boolean negation, and ‘*’ for testing for the existence of an attribute.

Boolean operators

These are ‘&&’ and ‘||’.

Parentheses ‘(’ and ‘)

These are used to change the precedence of operators, to introduce type casts (type coercions), to declare functions, and to pass actual arguments to functions.

Curly braces (‘{’ and ‘}’)

These are used to delimit blocks of code.


Numbers follow the usual C convention for integers. A number consisting of a sequence of digits is taken to be octal if it begins with ‘0’ (digit zero), and decimal otherwise. If the sequence of digits is preceded by ‘0x’ or ‘0X’, it is taken to be a hexadecimal integer.

IP Numbers

IP numbers are represented by a standard numbers-and-dots notation. IP numbers do not constitute a separate data type, rather they are in all respects similar to initeger numbers.


These follow the usual C convention for characters, i.e., they consist either of an ASCII character itself or of its value, enclosed in a pair of singlequotes. The character value begins with ‘\’ (backslash) and consists either of three octal or of two hexadecimal digits. A character does not form a special data type; it is represented internally by an integer.

Quoted strings

These follow slightly modified C conventions for strings. A string is a sequence of characters surrounded by double quotes, as in ‘"..."’. In a string, the double quote character ‘"’ must be preceeded by a backslash ‘\’. A ‘\’ and an immediately following newline are ignored. Following escape sequences have special meaning:


Audible bell character (ASCII 7)


Backspace (ASCII 8)


Escape character (ASCII 27)


Form feed (ASCII 12)


Newline (ASCII 10)


Carriage return (ASCII 13)


Horizontal tab (ASCII 9)




(‘o’ represents an octal digit) A character whose ASCII value is represented by the octal number ‘ooo’.


(‘H’ represents a hex digit) A character whose ASCII value is represented by the hex number ‘HH’.


Two characters ‘\(’.


Two characters ‘\)’.

If the character following the backslash is not one of those specified, the backslash is ignored.

Attribute values

The incoming request is passed implicitly to functions invoked via the Rewrite-Function attribute. It is kept as an associative array, whose entries can be accessed using the following syntax:

‘%[attribute-name]’ ‘(n)

The first form returns the value of the attribute attribute-name. Here attribute-name should be a valid Radius dictionary name (see section Dictionary of Attributes — ‘raddb/dictionary).

The second form returns the value of the nth attribute of type attribute-name. The index n is counted from zero, so


is equivalent to


Identifiers represent functions and variables. These are described in the next sub-subsection.

Regexp group references

A sequence of characters in the form


refers to the contents of parenthesized group number number obtained as a result of the last executed ‘=~’ command. The regexp group reference has always string data type. For example:

basename(string arg)
    if (arg =~ ".*/\(.*\)\..*")
        return \1;
        return arg;

This function strips from arg all leading components up to the last slash character, and all trailing components after the last dot character. It returns arg unaltered if it does not contain slashes and dots. It is roughly analogous to the system basename utility.

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A valid identifier is a string of characters meeting the following requirements:

  1. It starts with either a lower- or an uppercase letter of the Latin alphabet or either of the following symbols: ‘_’, ‘$’.
  2. It consists of alphanumeric characters, underscores(‘_’), and dollar signs (‘$’).

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Function declarations

A Rewrite function is declared as follows:

type function-name (parameter-list)

where type specifies the return type of the function, function-name declares the symbolic name of the function, and parameter-list declares the formal parameters to the function. It is a comma-separated list of declarations in the form

type parm-name

type being the parameter type, and parm-name being its symbolic name. Both function-name and parm-name should be valid identifiers.

Variable declarations

There are no global variables in Rewrite. All variables are local. The local variables are declared right after the opening curly brace (‘{’) and before any executable statements. The declaration syntax is

type ident_list ;

Here ident_list is either a valid Rewrite identifier or a comma-separated list of such identifiers.

Note that, unlike in C, no assignments are allowed in variable declarations.

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The Rewrite statements are: expressions, assignments, conditional statements, and return statements. A statement is terminated by a semicolon.


An expression is one of the following:

Type coercion

The type coercion is like a type cast in C. Its syntax is


The result of type coercion is as follows:


Variable type

Resulting conversion



No conversion. This results in the same integer value.



If the string value of the variable is a valid ASCII representation of the integer number (either decimal, octal, or hex), it is converted to the integer; otherwise the result of the conversion is undefined.



The ASCII representation (in decimal) of the integer number.



No conversion. This results in the same string value.


An assignment is

ident = expression ;

The variable ident is assigned the value of expression.

Function calls

These take the form

ident ( arg-list )

where ident is the identifier representing the function, and arg-list is a comma-separated list of expressions supplying actual arguments to the function. The number of the expressions must correspond exactly to the number of formal parameters in the function definition. The function that ident references can be either a compiled function or a built-in function.

delete’ statement

The ‘delete’ statement is used to delete an attribute or attributes from the incoming request. Its syntax is:

delete attribute-name;
delete attribute-name(n);

The first variant deletes all the attributes of the given type. The second variant deletes only the nth occurrence of the matching attribute.

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Rewrite uses POSIX regular expressions (See (regex)Top section `Regular Expression Library' in Regular Expression Library, for the detailed description of these).

You control the exact type of regular expressions by the use of the pragmatic comment regex. Its syntax is as follows:

#pragma regex option-list

Option-list is a whitespace-separated list of options. Each option is one of the following words prefixed with ‘+’ or ‘-’:


Use POSIX extended regular expression syntax when interpreting regular expressions.


Do not differentiate case. Subsequent regular expression comparisons will be case insensitive.


Match-any-character operators don't match a newline.

A non-matching list (‘[^...]’) not containing a newline does not match a newline.

Match-beginning-of-line operator (‘^’) matches the empty string immediately after a newline.

Match-end-of-line operator (‘$’) matches the empty string immediately before a newline.

Prefixing an option with ‘+’ means to enable the corresponding behavior. Prefixing it with ‘-’ means to disable it. Thus, the following statement:

#pragma regex +extended +icase

will enable extended POSIX regular expressions using case-insensitive comparison.

Using the following comment:

#pragma regex -extended 

will switch to the basic POSIX regular expressions.

The settings of a regex pragmatic comment remain in force up to the end of current source file, or to the next regex comment, whichever occurs first.

For compatibility with previous versions, GNU Radius uses the following defaults:

#pragma regex -extended -icase -newline

i.e. all regular expressions are treated as basic POSIX, comparison is case-sensitive.

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The following built-in functions are provided:

Function: integer length (string s)

Returns the length of the string s.

length("string") ⇒ 6
Function: integer index (string s, integer c)

Returns the index of the first occurrence of the character c in the string s. Returns -1 if no such occurrence is found.

index("/raddb/users", 47) ⇒ 0

index("/raddb/users", 45) ⇒ -1
Function: integer rindex (string s, integer i)

Returns the index of the last occurrence of the character c in the string s. Returns -1 if no such occurrence is found.

rindex("/raddb/users", 47) ⇒ 6
Function: string substr (string s, integer start, integer length)

Returns the substring of s of length at most length starting at position start.

substr("foo-bar-baz", 3, 5) ⇒ "-bar-"

All character positions in strings are counted from 0.

Function: string field (string buffer, integer n)

This function regards the buffer argument as consisting of fields separated with any amount of whitespace. It extracts and returns the nth field. n is counted from 1.

field("GNU's not UNIX", 1) ⇒ "GNU's"
field("GNU's not UNIX", 2) ⇒ "not"
field("GNU's not UNIX", 3) ⇒ "UNIX"
field("GNU's not UNIX", 4) ⇒ ""
Function: integer logit (string msg)

Outputs its argument to the Radius log channel info. Returns 0. For debugging purposes.

Function: integer inet_aton (string str)

Converts the Internet host address str from the standard numbers-and-dots notation into the equivalent integer in host byte order.

inet_aton("") ⇒ 2130706433
Function: string inet_ntoa (integer ip)

Converts the Internet host address ip given in host byte order to a string in standard numbers-and-dots notation.

inet_ntoa(2130706433) ⇒ ""
Function: integer htonl (integer n)

Converts the integer n, regarded as long, from host to network byte order.

Function: integer ntohl (integer n)

Converts the integer n, regarded as long, from network to host byte order.

Function: integer htons (integer n)

Converts the integer n, regarded as short, from host to network byte order.

Function: integer ntohs (integer n)

Converts the integer n, regarded as short, from network to host byte order.

Function: string gsub (string regex, string repl, string str)

For each substring matching the regular expression regex in the string str, substitute the string repl, and return the resulting string.

    ⇒ "StringS"
gsub("[0-9][0-9]*","N","28 or 29 days")
    ⇒ "N or N days"
gsub("[()'\"]","/","\"a\" (quoted) 'string'")
    ⇒ "/a/ /quoted/ /string/"
Function: string qprn (string str)

Replace all non-printable characters in string S by their corresponding hex value preceeded by a percent sign. Return the resulting string. Printable are alphabetical characters, decimal digits and dash (‘-’). Other characters are considered non-printable. For example:

qprn("a string/value") ⇒ "a%20string%2Fvalue"
Function: string quote_string (string str)

Replace all non-printable characters in string str by their three-digit octal code prefixed with a backslash, or by their C escape notation, as appropriate. Non-printable characters depend on the locale settings. For example, suppose that the current locale is set to ISO-8859-1 (a so called “Latin-1” character set) and ∗ represents a tab character. Then:

quote_string("François contains non∗printable chars")
  ⇒ "Fran\347ois contains non\tprintable chars"
Function: string unquote_string (string str)

Replace C escape notations in string str with corresponding characters using current locale. For example, for ISO-8859-1 locale:

unquote_string("Fran\347ois") ⇒ "François"
Function: string toupper (string str)

Returns the copy of the string str with all alphabetical characters converted to upper case. For example:

toupper("a-string") ⇒ "A-STRING"
Function: string tolower (string str)

Returns the copy of the string str with all alphabetical characters converted to lower case. For example:

tolower("A-STRING") ⇒ "a-string"
Function: string request_code_string (integer code)

Converts integer RADIUS request code to its textual representation as per RFC 3575. This function is useful in logging hooks (see section Logging hooks).

request_code_string(4) ⇒ "Accounting-Request"

Native Language Support

The native language support is provided via the functions described below. These functions are interfaces to GNU gettext library. For the information about general concepts and principles of Native Language Support, please refer to GNU gettext utilities: (gettext)Top section `gettext' in GNU gettext utilities.

The default current textual domain is ‘radius’.

Function: string textdomain (string domain)

Sets the new value for the current textual domain. This domain is used by the functions gettext and ngettext. Returns the name of the previously used domain.

Function: string gettext (string msgid)
Function: string _ (string msgid)

The function returns the translation of the string msgid if it is available in the current domain. If it is not available, the argument itself is returned.

The second form of this function provides a traditional shortcut notation.

For a detailed description of the GNU gettext interface, refer to (gettext)Interface to gettext section `Interface to gettext' in GNU gettext utilities.

Function: string dgettext (string domain, string msgid)

Returns the translation of the string msgid if it is available in the domain domain. If it is not available, the argument itself is returned.

Function: string ngettext (string msgid_singular, string msgid_plural, integer number)

The ngettext function is used to translate the messages that have singular and plural forms. The msgid_singular parameter must contain the singular form of the string to be converted. It is also used as the key for the search in the catalog. The msgid_plural parameter is the plural form. The parameter number is used to determine the plural form. If no message catalog is found msgid_singular is returned if number == 1, otherwise msgid_plural.

For a detailed description of the GNU gettext interface for the plural translation, refer to (gettext)Plural forms section `Additional functions for plural forms' in GNU gettext utilities.

Function: string dngettext (string domain, string msg_sing, string msg_plur, integer number)

Similar to ngettext, but searches translation in the given domain.

Request Accessors

The following functions are used to read some internal fields of a RADIUS request.

Function: Integer request_source_ip ()

Returns source IP address of the currently processed request. This function can be used to add NAS-IP-Address attribute to the requests lacking one, e.g.:

        if (!*%[NAS-IP-Address])
                %[NAS-IP-Address] = request_source_ip();
        return 0;
Function: Integer request_source_port ()

Returns the source UDP port.

Function: Integer request_id ()

Returns the request identifier.

Function: Integer request_code ()

Returns the request code.

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10.3 Guile

The name Guile stands for GNU's Ubiquitous Intelligent Language for Extensions. It provides a Scheme interpreter conforming to the R4RS language specification. This section describes use of Guile as an extension language for GNU Radius. It assumes that the reader is sufficiently familiar with the Scheme language. For information about the language, refer to (r4rs)Top section `Top' in Revised(4) Report on the Algorithmic Language Scheme. For more information about Guile, see (guile)Top section `Overview' in The Guile Reference Manual.

Scheme procedures can be called for processing both authentication and accounting requests. The invocation of a Scheme procedure for an authentication request is triggered by the Scheme-Procedure attribute; the invocation for an accounting request is triggered by the Scheme-Acct-Procedure attribute. The following sections address these issues in more detail.

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10.3.1 Data Representation

A/V pair lists are the main object Scheme functions operate upon. Scheme is extremely convenient for representation of such objects. A Radius A/V pair is represented by a Scheme pair; e.g.,

        Session-Timeout = 10

is represented in Guile as

        (cons "Session-Timeout" 10)

The car of the pair can contain either the attribute dictionary name or the attribute number. Thus, the above pair may also be written in Scheme as

        (cons 27 10)

(because Session-Timeout corresponds to attribute number 27).

Lists of A/V pairs are represented by Scheme lists. For example, the Radius pair list

        User-Name = "jsmith",
                User-Password = "guessme",
                NAS-IP-Address =,
                NAS-Port-Id = 10

is written in Scheme as

          (cons "User-Name" "jsmith")
          (cons "User-Password" "guessme")
          (cons "NAS-IP-Address" "")
          (cons "NAS-Port-Id" 10))

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10.3.2 Authentication with Scheme

The Scheme procedure used for authentication must be declared as follows:

Function Template: auth-function request-list check-list reply-list

Its arguments are:


The list of A/V pairs from the incoming request


The list of A/V pairs from the LHS of the profile entry that matched the request


The list of A/V pairs from the RHS of the profile entry that matched the request

The function return value determines whether the authentication will succeed. The function must return either a boolean value or a pair. The return of #t causes authentication to succeed. The return of #f causes it to fail.

For a function to add something to the reply A/V pairs, it should return a pair in the form

    (cons return-code list)

where return-code is a boolean value of the same meaning as described above. list is a list of A/V pairs to be added to the reply list. For example, the following function will always deny the authentication, returning an appropriate message to the user:

(define (decline-auth request-list check-list reply-list)
  (cons #f
         (cons "Reply-Message"
               "\r\nSorry, you are not
                allowed to log in\r\n"))))

As a more constructive example, let's consider a function that allows the authentication only if a user name is found in its internal database:

(define staff-data
   (list "scheme"
          (list (cons "NAS-IP-Address" ""))
          (list (cons "Framed-MTU" "8096")))
          (list (cons "Framed-MTU" "256"))))))
(define (auth req check reply)
  (let* ((username (assoc "User-Name" req))
         (reqlist (assoc username req))
         (reply-list '()))
    (if username
        (let ((user-data (assoc (cdr username) staff-data)))
          (rad-log L_INFO (format #f "~A" user-data))
          (if user-data
               (lambda (xx)
                  (lambda (pair)
                     ((avl-match? req (car pair))
                      (set! reply-list (avl-merge
                                        (cdr pair)))
                      (xx #t))))
                  (cdr user-data))

To trigger the invocation of the Scheme authentication function, assign its name to the Scheme-Procedure attribute in the RHS of a corresponding ‘raddb/users’ profile. For example:

        Scheme-Procedure = "auth"

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10.3.3 Accounting with Scheme

The Scheme accounting procedure must be declared as follows:

Function Template: acct-function-name request-list

Its argument is:


The list of A/V pairs from the incoming request

The function must return a boolean value. The accounting succeeds only if it has returned #t.

Here is an example of a Scheme accounting function. The function dumps the contents of the incoming request to a file:

(define radius-acct-file "/var/log/acct/radius")

(define (acct req)
  (call-with-output-file radius-acct-file
    (lambda (port)
      (for-each (lambda (pair)
                  (display (car pair) port)
                  (display "=" port)
                  (display (cdr pair) port)
                  (newline port))
      (newline port)))

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10.3.4 Radius-Specific Functions

Scheme Function: avl-delete av-list attr

Delete from av-list the pairs with attribute attr.

Scheme Function: avl-merge dst src

Merge src into dst.

Scheme Function: avl-match? target list

Return #t if all pairs from list are present in target.

Scheme Function: rad-dict-name->attr name

Return a dictionary entry for the given attribute name or #f if no such name was found in the dictionary.

A dictionary entry is a list in the form

Scheme List: dict-entry name-string attr-number type-number vendor

where the arguments are as follows:


The attribute name


The attribute number


The attribute type


The vendor PEC, if the attribute is a vendor-specific one, or #f otherwise.

Scheme Function: rad-dict-value->name attr value

Returns the dictionary name of the given value for an integer-type attribute attr, which can be either an attribute number or its dictionary name.

Scheme Function: rad-dict-name->value attr value

Convert a symbolic attribute value name into its integer representation.

Scheme Function: rad-dict-pec->vendor pec

Convert a PEC to the vendor name.

Scheme Function: rad-log-open prio

Open Radius logging to the severity level prio.

Scheme Function: rad-log-close

Close a Radius logging channel opened by a previous call to rad-log-open.

Scheme Function: rad-rewrite-execute-string string

Interpret string as an invocation of a function in Rewrite language and execute it.

Return value: return of the corresponding Rewrite call, translated to the Scheme data type.

Scheme Function: rad-rewrite-execute arglist

Execute a Rewrite language function. (car arglist) is interpreted as a name of the Rewrite function to execute, and (cdr arglist) as a list of arguments to be passed to it.

Return value: return of the corresponding Rewrite call, translated to the Scheme data type.

Scheme Function: rad-openlog ident option facility

Scheme interface to the system openlog() call.

Scheme Function: rad-syslog prio text

Scheme interface to the system syslog() call.

Scheme Function: rad-closelog

Scheme interface to the system closelog() call.

Scheme Function: rad-utmp-putent status delay list radutmp_file radwtmp_file

Write the supplied data into the radutmp file. If radwtmp_file is not nil, the constructed entry is also appended to wtmp_file.

list is:

Scheme List: utmp-entry user-name orig-name port-id port-type session-id caller-id framed-ip nas-ip proto

The user name


The original user name from the request


The value of the NAS-Port-Id attribute


A number or character indicating the port type


The session ID


The value of the Calling-Station-Id attribute from the request


The framed IP assigned to the user




A number or character indicating the type of the connection

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