JOH |
|
Jabber Over HTTP Tunnel |
Sergey Poznyakoff |
This edition of the JOH User Manual, last updated 31 March 2011, documents JOH Version 1.3.
Most site administrators use firewalls to protect their network from eventual abuse. Quite often such firewalls do not allow outbound connections to unknown and unused ports, including Jabber client connection port 5222/tcp, which makes it impossible to use Jabber services from inside such firewalls.
Several methods have been proposed so far to overcome this difficulty. The most reliable of them is Jabber HTTP Polling(1), which enables access to Jabber ports via HTTP requests.
Yet another method of accessing Jabber via HTTP is HTTP Connect. This method uses the HTTP ‘CONNECT’ command to establish a permanent connection to the remote Jabber server.
JOH supports both methods. The name JOH stands for Jabber Over HTTP. The package provides an easy to use proxy server for Jabber connections. It is intended for use by system administrators who wish to provide access to their Jabber serves via HTTP for those users who happen to be behind strict firewalls.
There are two most common scenarios for configuring Jabber Over HTTP proxy.
In the first scenario, you have a dedicated Jabber server and the port
80 (HTTP) is not used on that server. In this case you will use
standalone mode. In this mode johd
is configured
to listen on port 80 to proxy incoming requests to your
Jabber server and vice-versa.
In the second scenario, the port 80 is already in use by an HTTP
server running on the same box as your Jabber server. For such
cases, JOH provides a CGI mode. In this mode, you start
johd
to listen on an auxiliary port, and configure your
HTTP server to run a CGI program, joh.cgi
, which is included
in the package. The system then works as follows. HTTP polling
requests are received by your HTTP server, which invokes
joh.cgi
to handle them, In its turn, joh.cgi
extracts the necessary data from each request, reformats it and sends
it over to the johd
daemon over the auxiliary port. When
a subsequent request arrives, joh.cgi
receives the reply from
johd
, formats it as a HTTP response and sends it back to the
HTTP server, which sends it to the requesting client.
The CGI mode works only with HTTP Polling.
Of course, there may be combined cases, e.g.:
joh.cgi
would be installed on the HTTP server and johd
on the
Jabber server.
johd
in standalone mode on this machine
and configure it to communicate with your main Jabber server.
johd
Sockets Johd
reads its configuration from the command line. Only
the traditional short options are used. The order in which you place
options is important: some of them affect others that appear further
in the command line.
The ‘-l’ option configures a socket to listen on (hence its
mnemonics: listen). Its argument is an URL or address
specification for the socket. Normally, this specification is
the desired IP address and port number, separated by a colon. For
example, to have johd
listen on IP address 127.0.0.1, port
1111, you would write:
johd -l 127.0.0.1:1111 |
If you wish it to listen on a given port on all configured network interfaces, just specify that port alone, without a specific IP address, as in:
johd -l 1111 |
In fact, Johd
is able to work with three distinct
socket families: UNIX sockets, IPv4 and IPv6 inet addresses. There
are various ways to specify these. For a detailed discussion of them,
see URLs.
Any number of ‘-l’ options can be given: johd
will
open all required sockets and will listen for connections on any of
them.
The important point is the class of the socket to open. As you
already know, johd
works with two distinct socket classes:
HTTP sockets, which are supposed to receive data formatted in
accordance with the HTTP protocol, and auxiliary CGI sockets, which are designed
to communicate with joh.cgi
. By default, the latter is
assumed(2). The class of the socket to open is changed
by the ‘-c’ command line option: ‘-c HTTP’ tells
johd
to open all subsequent sockets for listening on HTTP
requests, and ‘-c CGI’ instructs it to open them for handling
internal CGI protocol data. The ‘-c’ option affects all
‘-l’ options that appear to the right of it in the command
line, until another ‘-c’ option is encountered, which changes
the default. To illustrate this, consider the following invocation:
johd -l 127.0.0.1:1111 \ -c HTTP -l 10.10.0.1 -l 192.168.0.2 \ -c CGI 10.10.0.1 |
It opens two sockets for auxiliary CGI: one at 127.0.0.1:1111 (it
appeared before the first ‘-c’ option and therefore belongs to the
default class, which is ‘CGI’) and the other at 10.10.0.1, which appears
after an explicit ‘-c CGI’. Notice that this later has no
port specification. If the port is missing. johd
will select
the default port for this class. The default port for ‘CGI’
is 1100(3), and the default for
‘HTTP’ is, of course, 80. Therefore, the command above will
listen for HTTP requests on 10.10.0.1:80 and 192.168.0.2:80.
Each incoming connection is validated via TCP
wrappers(4). The
default daemon (or service) name for validation coincides
with the name johd
was invoked with (i.e. is ‘johd’,
unless you renamed the program or started it via a symlink). However, the
validation rules will most probably depend on the class of socket that
received the connection: internal ‘CGI’ sockets in most cases should not
be visible outside your host, whereas ‘HTTP’ ones should be
accessible to everybody, Therefore, a special option is provided,
which changes the TCP wrapper service name for subsequent sockets.
This is the ‘-S’ option (mnemonics: Service name).
Similarly to ‘-c’, the ‘-S’ option affects all
‘-l’ options to the right of it, until another ‘-S’
option or end of the command line is encountered, whichever occurs
first.
Now, let's illustrate this by an improved version the example above:
johd -l 127.0.0.1:1111 \ -S johd-http -c HTTP -l 10.10.0.1 -l 192.168.0.2 \ -s johd-cgi -c CGI 10.10.0.1 |
In this configuration, the 127.0.0.1:1111 socket will be protected by the TCP service name ‘johd’, the two ‘HTTP’ sockets — by service name ‘johd-http’ and the ‘CGI’ socket 10.10.0.1 — by service name ‘johd-cgi’.
Connections to remote Jabber servers are also validated using TCP wrappers. However, they use different service name. The service name for validating a requested jabber connection is created using the following pattern:
srvname/jabber@ipaddr |
where srvname is the TCP service name, as described above, and ipaddr is the IP address of the server.
Configuring johd
to work in standalone mode is pretty
straightforward: all you have to do is give it an address (or
addresses) to listen on and instruct it to open these addresses in
‘HTTP’ class. In a simplest case, the following command will do:
johd -c HTTP |
It will instruct johd
to listen on port 80 on all configured
network interfaces. To select a particular address or addresses to
listen on, use the ‘-l’ option, as described in the previous
section.
It is important to configure your ‘/etc/hosts.allow’ to control accesses to the incoming HTTP port and outgoing Jabber connections. For example, the two lines below allow access to HTTP from anywhere and grant anybody the right to request any Jabber servers:
johd: ALL johd/jabber@ALL: ALL |
As a more complex example, the entries below allow access to HTTP from anywhere and limit the use of Jabber servers to 208.68.163.220 and 192.168.10.1. The use of 208.68.163.220 is granted to anybody, and the use of 192.168.10.1 is allowed only for clients coming from IP addresses in the range 192.168.0.1 — 192.168.0.254.
johd: ALL johd/jabber@208.68.163.220: ALL johd/jabber@192.168.10.1: 192.168.10.0/24 |
The ‘CGI’ mode is a bit more complicated, because it involves
configuring two components. However, the default settings are chosen
so as to simplify the configuration. First, select the socket to use
for interprocess communication between johd
and
joh.cgi
. If both processes run on the same box, then
‘localhost’ or some UNIX socket is a natural choice. Now, start the
daemon:
johd -l 127.0.0.1 |
Make sure the socket 127.0.0.1:1100 is accessible from localhost. In particular, if your ‘/etc/hosts.deny’ contains the line ‘ALL: ALL’, place this in your ‘/etc/hosts.allow’:
johd: 127.0.0.1 |
Similarly, make sure outgoing connections to selected Jabber servers are allowed for localhost:
johd/jabber@213.130.31.41: 127.0.0.1 |
Then copy joh.cgi
to your ‘cgi-bin’ directory and
you're done. You might also wish to configure your HTTP server to use
some good-looking alias for that. For example, in my Apache
configuration I use:
Alias /http-poll /var/www/cgi-bin/joh.cgi |
If your HTTP server and johd
are running on different
machines, you will need to inform joh.cgi
about the
address johd
is listening on. Suppose, for example, that
johd
is running on machine ‘A’ and is listening on
IP address 192.168.0.1, port 1100. The HTTP server is running on
the machine ‘B’, which has IP address 192.168.0.2. To tell
joh.cgi
it must connect to ‘192.168.0.1:1100’, set
the environment variable JOH_SERVER_URL
. For example, if
‘B’ is running Apache, then in your ‘httpd.conf’ you would
set:
SetEnv JOH_SERVER_URL 192.168.0.1:1100 |
Notice also, that you need to ensure that this socket on the box ‘A’ is accessible only to 192.168.0.2. For example:
johd: ALL |
johd: 192.168.0.2 |
johd
One of the basic assumptions made when designing johd
was
that it was to be run as a transport within Jabber configuration.
Therefore, after startup, johd
remains in the foreground and
does not disconnect from the controlling terminal. It also normally
sends all its diagnostic messages to the standard error output (but
see section Logging and Debugging, below.
To start jabber2
components we recommend using GNU
Pies
, instead of the default simple program manager shipped
with Jabberd2
. Pies
offers considerable
flexibility in handling jabber components. For a detailed description
of Pies, GNU Pies Manual: (pies)Top section `Top' in GNU Pies Manual. For an
example of Jabberd2
configuration with Pies, refer to
http://www.gnu.org.ua/software/pies/example.php?what=jabberd2.
To configure Pies to start johd
, add the following component
statement to your configuration file:
component johd { command "johd options"; strderr syslog err; }; |
Replace johd with the full pathname of the johd
binary, and options with the desired command line options.
For example:
component johd { command "/usr/sbin/johd -c HTTP"; strderr syslog err; }; |
Another way to start johd
is independently of the Jabber
server. To do so, give it the ‘-D’ command line option. This
option instructs johd
to disconnect from the controlling
terminal and run in the background as a daemon. Diagnostic messages
are then sent to the syslog, using the ‘daemon’ facility (this
can be changed using the ‘-F’ option; see section Logging and Debugging).
Normally, johd
continues its operation with the privileges
of the user who started it. If this user is root, you may wish
johd
to run as some other user. To do so, use the
‘-u’ option, e.g.:
johd -cHTTP -D -u nobody |
The daemon switches to new user after completing operations that require root privileges, such as, e.g. creating sockets that listen on ports below 1024, etc.
When starting johd
in daemon mode, it is also common to give
it the ‘-p’ option. This option takes a file name as argument
and causes the program to write its PID to that file after switching
to the background. If this file already exists, johd
will
read the PID from it and will check if a process with that PID is
actually running. If so, johd
refuses to startup and
outputs an appropriate diagnostics. Otherwise, it will overwrite the
file with the new PID value.
If both ‘-u’ and ‘-p’ are used, the pidfile is opened after switching to the user provileges. In this case, you should make sure the directory component of the pidfile is writable for the user supplied with the ‘-u’ option.
Following is an example startup command:
johd -D -p /var/run/johd.pid |
To automate startup and shutdown of johd
in daemon mode, use
the following shell script:
#! /bin/sh PIDFILE=/var/run/johd.pid case $1 in start) /usr/bin/johd -D -p $PIDFILE;; stop) test -f $PIDFILE && kill -TERM `cat $PIDFILE`;; restart) $0 stop $0 start;; *) echo >&2 "usage: $0 {start|stop|restart}" esac |
Proxying of Jabber connections is requested by HTTP requests
with either ‘POST’ or ‘CONNECT’ methods. Any other requests
received by johd
are normally dropped. However, ‘GET’
requests are handled separately. Normally, an incoming ‘GET’
request means that someone has pointed his web browser to the URL
served by johd
. When such a request arrives, johd
replies with a 404 response code. A compiled-in error page is sent
back in the response. This behavior can be customized in two ways.
First, you can supply a custom error page using the ‘-E’ command line option. The argument to this option must specify an absolute pathname to a valid HTML file. The contents of this file will be sent back in 404 responses.
Similarly to ‘-c’ and ‘-S’ options, the ‘-E’ option applies to all HTTP sockets created by subsequent ‘-l’ options which appear to the right of it, until another ‘-E’ or ‘-R’ option (see below) is encountered.
An example usage follows:
johd -c HTTP -E /etc/joh/404.html -l 10.10.10.1 |
Another way to handle ‘GET’ requests is to return a 303 response, redirecting the requester to another HTTP resource. This is achieved via the ‘-R’ option. Its argument is a valid URL, beginning with a ‘http://’. For example:
johd -c HTTP -R http://www.example.net/jabber |
Notice, that ‘-E’ and ‘-R’ options are mutually
exclusive. For example, the following invocation will reply
to ‘GET’ requests arriving to ‘10.10.10.1’ with the
error page read from ‘/etc/joh/404.html’, and will redirect any
‘GET’ request arriving to ‘10.10.10.2’ to
<http://www.example.net/jabber
>:
johd -c HTTP -E /etc/joh/404.html -l 10.10.10.1 \ -R http://www.example.net/jabber -l 10.10.10.2 |
The ‘joh.cgi’ utility provides similar features, except that it cannot send back a ‘404’ response.
If any request other than ‘POST’ arrives, ‘joh.cgi’
replies with the compiled-in error page, just as johd
does.
If the JOH_ERROR_PAGE
environment variable is set, and its value points
to a readable file, this file's contents is sent back instead.
If JOH_ERROR_REDIRECT
variable is set and its value is a URL
which begins with ‘http://’, joh.cgi
responds with a
redirection to that URL.
Normally, johd
prints any errors, warnings and other
diagnostic messages on standard error. You can, however, change this
default and direct all diagnostic messages to syslog. To do so,
specify the desired syslog facility with the ‘-F’ command line
option. For example:
johd -F daemon |
Allowed facility names for use with this option are: ‘user’, ‘daemon’, ‘auth’, ‘authpriv’, ‘mail’, ‘cron’, ‘local0’ through ‘local7’. All names are case-insensitive.
Notice, that when given the ‘-D’ option (see daemon),
johd
automatically assumes ‘-F daemon’, so you need
not use the ‘-F’ option, unless, of course, you want to change
the default facility.
Messages sent to syslog are prefixed by the program name. To change this prefix use the ‘-L’ option. Its argument will be used as a log tag to prefix each message with.
Each diagnostic message has a severity level associated with it. Severity levels are (in order of increasing severity): ‘debug’, ‘warning’, ‘info’, ‘error’, and ‘crit’. The latter is assigned to conditions which cause immediate termination of the program.
Normally, severity levels are not printed. To instruct johd
to precede each message with its severity level, use the ‘-P’
option.
Debugging diagnostics is useful when you trace some difficult
configuration problem or investigate a bug in johd
itself.
This diagnostics is printed only when the ‘-d’ option is given.
The argument to the ‘-d’ option is the debugging level,
an integer number ranging from 0 to 100. Level 0 effectively disables
all debugging and is equivalent to not specifying ‘-d’ option
at all. Subsequent levels produce increasing amount of debugging
information. Finally, the level 100 prints dumps of network packets
received and sent by johd
.
Notice, that the use of the ‘-d’ option with levels greater
than 10 requires a good knowledge about johd
internals and
slows down its operation, so use it sparingly, if at all.
When debugging johd
it may be helpful to know where
precisely in the source code each debugging message was generated.
This information can be obtained using the ‘-i’
(source-info) option. When it is given, each debug message is
additionally prefixed with the name of the source file and line number
in it.
The following table summarizes the available command line options in alphabetic order. For each option, it provides a reference to the place in the tutorial where the option is discussed.
Sets socket class. Allowed values for class are ‘CGI’ and ‘HTTP’. This option affects all subsequent ‘-l’ options appearing to the right of it, until another ‘-c’ option or end of command line is encountered, whichever occurs first.
See socket class.
After startup, switch to the background and run as daemon. See daemon.
Sets debugging level. See section Logging and Debugging.
Read the 404 error page from file. This error page is returned as a response to HTTP GET requests. The file must contain a valid HTML document without external references in the ‘head’ section. See section HTTP GET Requests.
This option affects all HTTP sockets created by subsequent ‘-l’ options which appear to the right of it, until another ‘-E’ option or end of command line is encountered, whichever occurs first.
Sets syslog facility. Allowed values for facility are: ‘user’, ‘daemon’, ‘auth’, ‘authpriv’, ‘mail’, ‘cron’, ‘local0’ through ‘local7’. All names are case-insensitive.
See section Logging and Debugging.
Shows a terse help summary.
Show source line information with debug messages. See section Logging and Debugging.
Sets log tag. See section Logging and Debugging.
Listen on the given url. Several ‘-l’ options can appear in the command line.
See listen option.
Prefix diagnostic messages with their severity level. See section Logging and Debugging.
Write PID to file. See daemon.
Redirect HTTP GET requests to url. The argument must begin with ‘http://’. See section HTTP GET Requests.
This option affects all HTTP sockets created by subsequent ‘-l’ options which appear to the right of it, until another ‘-R’ option or end of command line is encountered, whichever occurs first.
Sets service name for TCP wrappers. This option affects all subsequent ‘-l’ options appearing to the right of it, until another ‘-S’ option or end of command line is encountered, whichever occurs first.
See TCP wrappers.
Sets URL of the default jabber server. It is used if the request does not specify the server explicitly.
Sets session idle timeout. Type is the type of the socket: ‘C’ for client sockets (either ‘CGI’ or ‘HTTP’) and ‘J’ for Jabber socket. Timeout is the timeout value, either in seconds or in ‘XhYmZs’ form.
Defaults are: ‘-t C:5m -t J:1m’.
Run as user, after completing privileged operations, such as creating sockets that listen on ports below 1024. See daemon.
Prints the program version.
JOH components are able to handle three socket families: UNIX sockets, IPv4 and IPv6. URLs provide a uniform way of specifying socket addresses in any of these families.
A URL consists of the following parts:
scheme://adress:port |
Up to two parts can be omitted, if that does not create ambiguity.
Valid URL schemes are:
Specifies a UNIX socket. The address part is the socket pathname, and the ‘:port’ part is not used. The pathname must be absolute, e.g. ‘unix:///var/run/joh.socket’.
To facilitate typing, the two slashes after the colon can be omitted, as in:
unix:/var/run/joh.socket |
Specifies an IPv4 socket. The address part must be an IPv4 address in dotted quad form, or a host name. If the latter resolves to multiple addresses, those belonging to the IPv4 family are selected. The port part is either the network port number in decimal, or a corresponding service name from ‘/etc/services’. For example:
inet://127.0.0.1:1100 |
Specifies an IPv6 socket. The address part must be either an IPv6 address in numeric notation enclosed in square brackets or a host name. If the latter resolves to multiple addresses, those belonging to the IPv6 family are selected. The port part is either the network port number in decimal, or a corresponding service name from ‘/etc/services’. E.g.:
inet6://[::1]:1100 |
For URLs given as argument to the ‘-l’ option, either address or port can be omitted. If address is omitted, the program will listen on all available network interfaces with addresses from the specified family, e.g.:
inet6://:1100 |
instructs johd
to listen on port 1100 on all IPv6 interfaces.
If port is omitted, the default is selected depending upon the class of the socket: 1100 is used for ‘CGI’ sockets, and 80 is used for ‘HTTP’ sockets.
The port component can also be omitted in URLs which are arguments to the ‘-s’ option (see default jabber server). In this case, port defaults to 5222, e.g.:
inet6://[::1] inet://127.0.0.1 |
For compatibility with earlier versions, johd
accepts IPv6
addresses without square brackets, although such use is not
recommended, e.g.:
inet6://::1:1100 |
If the scheme part is omitted, johd
tries to do its best
to guess what address family is assumed. Thus:
‘/var/run/socket’ is treated as ‘unix:///var/run/socket’;
‘127.0.0.1’ is treated as ‘inet://127.0.0.1’;
‘[::1]:3398’ is treated as ‘inet6://[::1]:3398’;
‘::1:3398’ is treated as ‘inet6://[::1]:3398’;
The URL ‘3456’ causes johd
to listen on port 3456 on
all available network interfaces, no matter what their address family is.
Depending on the reason for termination, johd
exits with
the following codes:
Normal termination. This includes, e.g., termination on ‘SIGTERM’ signal.
Usage error, e.g. unknown option or erroneous argument was given in the command line.
A service is unavailable. This happens, for instance, if the program could not fork or disconnect from the controlling terminal.
An internal software error has been detected. If it ever happens, please report this as bug. See section How to Report a Bug.
Temporary error condition. Currently this happens if the ‘-p file’ option is specified, file exists, but cannot be accessed.
A configuration error occurred. This is different from usage error (64) in that the data supplied to the program where syntactically correct, but cannot be used. For example, a host name supplied with ‘-l’ cannot be resolved.
The following signals cause immediate program termination with exit code 0: ‘SIGPIPE’, ‘SIGINT’, ‘SIGQUIT’, ‘SIGTERM’, ‘SIGHUP’.
If you need to run johd
on a box which already runs an HTTP
server, it is impossible to have johd
handle HTTP
connections directly, because port 80 is already in use. The solution
then is to use joh.cgi
within your HTTP server and to start
johd
in CGI mode. This approach is discussed in detail in
CGI Mode.
The usual way to run joh.cgi
is to copy it to your
‘cgi-bin’ directory and to provide an alias for it. For example,
in Apache ‘httpd.conf’:
Alias /http-poll /var/www/cgi-bin/joh.cgi |
The built-in default configuration is sufficient for most cases. If,
however, you need to configure joh.cgi
, you can do so via
the following environment variables:
JOH_SERVER_URL
Sets the URL of the johd
server. Default is ‘127.0.0.1:1100’.
JOH_JABBER_SERVER_URL
Sets the URL of the default Jabber server. This value is used when the incoming HTTP request does not specify server and port explicitly.
The default value is ‘inet://gnu.org.ua’.
JOH_JABBER_SERVER
Specifies the IP address of the default Jabber server.
JOH_JABBER_PORT
Sets the port name of the default Jabber server.
JOH_ERROR_PAGE
If any request other than ‘POST’ arrives, return the contents of the file specified in the value of this variable. See joh.cgi bad request handling.
JOH_ERROR_REDIRECT
If any request other than ‘POST’ arrives, redirect it to the URL supplied in this variable. See joh.cgi bad request handling.
Please, report bugs and suggestions to gray+joh@gnu.org.ua.
You hit a bug if at least one of the conditions below is met:
johd
of joh.cgi
terminate on signal 11
(SIGSEGV) or 6 (SIGABRT).
johd
terminates with exit code 70 (internal software
error)
If you think you've found a bug, please be sure to include maximum information available to reliably reproduce it, or at least to analyze it. The information needed is:
Any errors, typos or omissions found in this manual also qualify as bugs. Please report them, if you happen to find any.
Version 1.2, November 2002
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The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.
A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.
The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.
You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.
You may also lend copies, under the same conditions stated above, and you may publicly display copies.
If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.
If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.
If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.
It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.
You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:
If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.
You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.
You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.
The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.
You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.
The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.
In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”
You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.
You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.
A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.
If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.
Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.
If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.
You may not copy, modify, sublicense, or distribute the Document except as expressly provided for under this License. Any other attempt to copy, modify, sublicense or distribute the Document is void, and will automatically terminate your rights under this License. However, parties who have received copies, or rights, from you under this License will not have their licenses terminated so long as such parties remain in full compliance.
The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See http://www.gnu.org/copyleft/.
Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation.
To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:
Copyright (C) year your name. Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.2 or any later version published by the Free Software Foundation; with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license is included in the section entitled ``GNU Free Documentation License''. |
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:
with the Invariant Sections being list their titles, with the Front-Cover Texts being list, and with the Back-Cover Texts being list. |
If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.
If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.
This is a general index of all issues discussed in this manual
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See http://xmpp.org/extensions/xep-0025.html.
The decision which class to take as the default is somehow arbitrary, we might as well have chosen HTTP, but historically it happened to be CGI.
Again, the choice was somewhat arbitrary, but we know of no other service using this number.
See hosts_access(5), for detailed description of TCP wrapper access control files.
Note also, that this feature can be disabled at compile time, by
the ‘--without-tcp-wrappers’ option to configure
,
although this is highly unrecommended.
This document was generated by Sergey Poznyakoff on March, 31 2011 using texi2html 1.78.
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