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the FastCGI Interface
Module: mod_fastcgi
:Author: Jan Kneschke
:Date: $Date: 2004/11/03 22:26:05 $
:Revision: $Revision: 1.3 $
The FastCGI interface is the fastest and most secure way
to interface external process-handlers like Perl, PHP and
your self-written applications.
.. meta::
:keywords: lighttpd, FastCGI
.. contents:: Table of Contents
lighttpd provides an interface to a external programs that
support the FastCGI interface. The FastCGI Interface is
defined by and is a
platform-independent and server independent interface between
a web-application and a webserver.
This means that FastCGI programs that run with the Apache
Webserver will run seamlessly with lighttpd and vice versa.
FastCGI is removes a lot of the limitations of CGI programs.
CGI programs have the problem that they have to be restarted
by the webserver for every request which leads to really bad
performance values.
FastCGI removes this limitation by keeping the process running
and handling the requests by this always running process. This
removes the time used for the fork() and the overall startup
and cleanup time which is necessary to create and destroy a
While CGI programs communicate to the server over pipes,
FastCGI processes use Unix-Domain-Sockets or TCP/IP to talk
with the webserver. This gives you the second advantage over
simple CGI programs: FastCGI don't have to run on the Webserver
itself but everywhere in the network.
lighttpd takes it a little bit further by providing a internal
FastCGI load-balancer which can be used to balance the load
over multiple FastCGI Servers. In contrast to other solutions
only the FastCGI process has to be on the cluster and not the
whole webserver. That gives the FastCGI process more resources
than a e.g. load-balancer+apache+mod_php solution.
If you compare FastCGI against a apache+mod_php solution you
should note that FastCGI provides additional security as the
FastCGI process can be run under different permissions that
the webserver and can also live a chroot which might be
different than the one the webserver is running in.
lighttpd provides the FastCGI support via the fastcgi-module
(mod_fastcgi) which provides 2 options in the config-file:
a value between 0 and 65535 to set the debug-level in the
FastCGI module. Currently only 0 and 1 are used. Use 1 to
enable some debug output, 0 to disable it.
tell the module where to send FastCGI requests to. Every
file-extension can have it own handler. Load-Balancing is
done by specifying multiple handles for the same extension.
structure of fastcgi.server section: ::
( <extension> =>
( "host" => <string> ,
"port" => <integer> ,
"socket" => <string>, # either socket
# or host+port
"bin-path" => <string>, # OPTIONAL
"bin-environment" => <array>, # OPTIONAL
"bin-copy-environment" => <array>, # OPTIONAL
"mode" => <string>, # OPTIONAL
"docroot" => <string> , # OPTIONAL if "mode"
# is not "authorizer"
"check-local" => <string>, # OPTIONAL
"min-procs" => <integer>, # OPTIONAL
"max-procs" => <integer>, # OPTIONAL
"max-load-per-proc" => <integer>, # OPTIONAL
"idle-timeout" => <integer>, # OPTIONAL
"broken-scriptfilename" => <boolean>, # OPTIONAL
"disable-time" => <integer>, # optional
"allow-x-send-file" => <boolean> # optional
( "host" => ...
:<extension>: is the file-extension or prefix
(if started with "/")
:"host": is hostname/ip of the FastCGI process
:"port": is tcp-port on the "host" used by the FastCGI
:"bin-path": path to the local FastCGI binary which should be
started if no local FastCGI is running
:"socket": path to the unix-domain socket
:"mode": is the FastCGI protocol mode.
Default is "responder", also "authorizer"
mode is implemented.
:"docroot": is optional and is the docroot on the remote
host for default "responder" mode. For
"authorizer" mode it is MANDATORY and it points
to docroot for authorized requests. For security
reasons it is recommended to keep this docroot
outside of server.document-root tree.
:"check-local": is optional and may be "enable" (default) or
"disable". If enabled the server first check
for a file in local server.document-root tree
and return 404 (Not Found) if no such file.
If disabled, the server forward request to
FastCGI interface without this check.
:"broken-scriptfilename": breaks SCRIPT_FILENAME in a wat that
PHP can extract PATH_INFO from it (default: disabled)
:"disable-time": time to wait before a disabled backend is checked
:"allow-x-send-file": controls if X-LIGHTTPD-send-file headers
are allowed
If bin-path is set:
:"min-procs": sets the minium processes to start
:"max-procs": the upper limit of the processess to start
:"max-load-per-proc": maximum number of waiting processes on
average per process before a new process is
:"idle-timeout": number of seconds before a unused process
gets terminated
:"bin-environment": put an entry into the environment of
the started process
:"bin-copy-environement": clean up the environment and copy
only the specified entries into the fresh
environment of the spawn process
Multiple extensions for the same host ::
fastcgi.server = ( ".php" =>
(( "host" => "",
"port" => 1026,
"bin-path" => "/usr/local/bin/php"
".php4" =>
(( "host" => "",
"port" => 1026
Example with prefix: ::
fastcgi.server = ( "/remote_scripts/" =>
(( "host" => "",
"port" => 9000,
"check-local" => "disable",
"docroot" => "/" # remote server may use
# it's own docroot
The request `` will
be forwarded to fastcgi server at and the value
"/remote_scripts/test.cgi" will be used for the SCRIPT_NAME
variable. Remote server may prepend it with its own
document root. The handling of index files is also the
resposibility of remote server for this case.
In the case that the prefix is not terminated with a slash
the prefix will be handled as file and /test.cgi would become
a PATH_INFO instead of part of SCRIPT_NAME.
Example for "authorizer" mode: ::
fastcgi.server = ( "/remote_scripts/" =>
(( "host" => "",
"port" => 9000,
"docroot" => "/path_to_private_docs",
"mode" => "authorizer"
Note that if "docroot" is specified then its value will be
used in DOCUMENT_ROOT and SCRIPT_FILENAME variables passed
to FastCGI server.
The FastCGI plugin provides automaticly a load-balancing between
multiple FastCGI servers. ::
fastcgi.server = ( ".php" =>
(( "host" => "", "port" => 1030 ),
( "host" => "", "port" => 1030 ))
To understand how the load-balancing works you can enable the
fastcgi.debug option and will get a similar output as here: ::
proc: 1031 1 1 1 31454
proc: 1028 1 1 1 31442
proc: 1030 1 1 1 31449
proc: 1029 1 1 2 31447
proc: 1026 1 1 2 31438
got proc: 34 31454
release proc: 40 31438
proc: 1026 1 1 1 31438
proc: 1028 1 1 1 31442
proc: 1030 1 1 1 31449
proc: 1031 1 1 2 31454
proc: 1029 1 1 2 31447
Even if this for multiple FastCGI children on the local machine
the following explaination is valid for remote connections too.
The output shows:
- IP, port, unix-socket (is empty here)
- is-local, state (0 - unset, 1 - running, ... )
- active connections (load)
As you can see the list is always sorted by the load field.
Whenever a new connection is requested, the first entry (the one
with the lowest load) is selected, the load is increased (got proc: ...)
and the list is sorted again.
If a FastCGI request is done or the connection is dropped, the load on the
FastCGI proc decreases and the list is sorted again (release proc: ...)
This behaviour is very light-weight in code and still very efficient
as it keeps the fastcgi-servers equally loaded even if they have different
Adaptive Process Spawning
.. note:: This feature is disabled in 1.3.14 again. min-procs is
ignored in that release
Starting with 1.3.8 lighttpd can spawn processes on demand if
a bin-path is specified and the FastCGI process runs locally.
If you want to have a least one FastCGI process running and
more of the number of requests increases you can use min-procs
and max-procs.
A new process is spawned as soon as the average number of
requests waiting to be handle by a single process increases the
max-load-per-proc setting.
The idle-timeout specifies how long a fastcgi-process should wait
for a new request before it kills itself.
fastcgi.server = ( ".php" =>
(( "socket" => "/tmp/php.socket",
"bin-path" => "/usr/local/bin/php",
"min-procs" => 1,
"max-procs" => 32,
"max-load-per-proc" => 4,
"idle-timeout" => 20
Disabling Adaptive Spawning
Adaptive Spawning is a quite new feature and it might misbehave
for your setup. There are several ways to control how the spawing
is done:
1. ``"max-load-per-proc" => 1``
if that works for you, great.
2. If not set ``min-procs == max-procs``.
3. For PHP you can also use: ::
$ PHP_FCGI_CHILDREN=384 ./lighttpd -f ./lighttpd.conf
fastcgi.server = ( ".php" =>
(( "socket" => "/tmp/php.socket",
"bin-path" => "/usr/local/bin/php",
"min-procs" => 1,
"max-procs" => 1,
"max-load-per-proc" => 4,
"idle-timeout" => 20
It will create one socket and let's PHP create the 384 processes itself.
4. If you don't want lighttpd to manage the fastcgi processes, remove the
bin-path and use spawn-fcgi to spawn them itself.
FastCGI and Programming Languages
Preparing PHP as a FastCGI program
One of the most important application that has a FastCGI
interface is php which can be downloaded from . You have to recompile the php from
source to enable the FastCGI interface as it is normally
not enabled by default in the distributions.
If you already have a working installation of PHP on a
webserver execute a small script which just contains ::
<?php phpinfo(); ?>
and search for the line in that contains the configure call.
You can use it as the base for the compilation.
You have to remove all occurences of `--with-apxs`, `--with-apxs2`
and the like which would build PHP with Apache support. Add the
next three switches to compile PHP with FastCGI support::
$ ./configure \
--enable-fastcgi \
--enable-force-cgi-redirect \
After compilation and installation check that your PHP
binary contains FastCGI support by calling: ::
$ php -v
PHP 4.3.3RC2-dev (cgi-fcgi) (built: Oct 19 2003 23:19:17)
The important part is the (cgi-fcgi).
Starting a FastCGI-PHP
Starting with version 1.3.6 lighttpd can spawn the FastCGI
processes locally itself if necessary: ::
fastcgi.server = ( ".php" =>
(( "socket" => "/tmp/php-fastcgi.socket",
"bin-path" => "/usr/local/bin/php"
PHP provides 2 special environment variables which control the number of
spawned workes under the control of a single watching process
(PHP_FCGI_CHILDREN) and the number of requests what a single worker
handles before it kills itself. ::
fastcgi.server = ( ".php" =>
(( "socket" => "/tmp/php-fastcgi.socket",
"bin-path" => "/usr/local/bin/php",
"bin-environment" => (
To increase the security of the started process you should only pass
the necessary environment variables to the FastCGI process. ::
fastcgi.server = ( ".php" =>
(( "socket" => "/tmp/php-fastcgi.socket",
"bin-path" => "/usr/local/bin/php",
"bin-environment" => (
"PHP_FCGI_MAX_REQUESTS" => "10000" ),
"bin-copy-environment" => (
Configuring PHP
If you want to use PATH_INFO and PHP_SELF in you PHP scripts you have to
configure php and lighttpd. The php.ini needs the option: ::
cgi.fix_pathinfo = 1
and the option ``broken-scriptfilename`` in your fastcgi.server config: ::
fastcgi.server = ( ".php" =>
(( "socket" => "/tmp/php-fastcgi.socket",
"bin-path" => "/usr/local/bin/php",
"bin-environment" => (
"PHP_FCGI_MAX_REQUESTS" => "10000" ),
"bin-copy-environment" => (
"PATH", "SHELL", "USER" ),
"broken-scriptfilename" => "enable"
Why this ? the ``cgi.fix_pathinfo = 0`` would give you a working ``PATH_INFO``
but no ``PHP_SELF``. If you enable it, it turns around. To fix the
``PATH_INFO`` `--enable-discard-path` needs a SCRIPT_FILENAME which is against the CGI spec, a
broken-scriptfilename. With ``cgi.fix_pathinfo = 1`` in php.ini and
``broken-scriptfilename => "enable"`` you get both.
External Spawning
Spawning FastCGI processes directly in the webserver has some
disadvantages like
- FastCGI process can only run locally
- has the same permissions as the webserver
- has the same base-dir as the webserver
As soon as you are using a seperate FastCGI Server to
take off some load from the webserver you have to control
the FastCGI process by a external program like spawn-fcgi.
spawn-fcgi is used to start a FastCGI process in its own
environment and set the user-id, group-id and change to
another root-directory (chroot).
For convenience a wrapper script should be used which takes
care of all the necessary option. Such a script in included
in the lighttpd distribution and is call
The script has a set of config variables you should take
a look at: ::
## ABSOLUTE path to the spawn-fcgi binary
## ABSOLUTE path to the PHP binary
## bind to tcp-port on localhost
## bind to unix domain socket
# FCGISOCKET="/tmp/php.sock"
## number of PHP childs to spawn
## number of request server by a single php-process until
## is will be restarted
## IP adresses where PHP should access server connections
## from
# allowed environment variables sperated by spaces
## if this script is run as root switch to the following user
If you have set the variables to values that fit to your
setup you can start it by calling: ::
spawn-fcgi.c.136: child spawned successfully: PID: 6925
If you get "child spawned successfully: PID:" the php
processes could be started successfully. You should see them
in your processlist: ::
$ ps ax | grep php
6925 ? S 0:00 /usr/local/bin/php
6928 ? S 0:00 /usr/local/bin/php
The number of processes should be PHP_FCGI_CHILDREN + 1.
Here the process 6925 is the master of the slaves which
handle the work in parallel. Number of parallel workers can
be set by PHP_FCGI_CHILDREN. A worker dies automaticly of
handling PHP_FCGI_MAX_REQUESTS requests as PHP might have
memory leaks.
If you start the script as user root php processes will be
running as the user USERID and group GROUPID to drop the
root permissions. Otherwise the php processes will run as
the user you started script as.
As the script might be started from a unknown stage or even
directly from the command-line it cleans the environment
before starting the processes. ALLOWED_ENV contains all
the external environement variables that should be available
to the php-process.
For Perl you have to install the FCGI module from CPAN.
For TCL ...
Skeleton for remote authorizer
The basic functionality of authorizer is as follows (see, 6.3 for
details). ::
#include <fcgi_stdio.h>
#include <stdlib.h>
#include <unistd.h>
int main () {
char* p;
while (FCGI_Accept() >= 0) {
/* wait for fastcgi authorizer request */
printf("Content-type: text/html\r\n");
if ((p = getenv("QUERY_STRING")) == NULL) ||
<QUERY_STRING is unauthorized>)
printf("Status: 403 Forbidden\r\n\r\n");
else printf("\r\n");
/* default Status is 200 - allow access */
return 0;
It is possible to use any other variables provided by
FastCGI interface for authorization check. Here is only an
fastcgi.debug should be enabled for troubleshooting.
If you get: ::
(fcgi.c.274) connect delayed: 8
(fcgi.c.289) connect succeeded: 8
(fcgi.c.745) unexpected end-of-file (perhaps the fastcgi
process died): 8
the fastcgi process accepted the connection but closed it
right away. This happens if FCGI_WEB_SERVER_ADDRS doesn't
include the host where you are connection from.
If you get ::
(fcgi.c.274) connect delayed: 7
(fcgi.c.1107) error: unexpected close of fastcgi connection
for /peterp/seite1.php (no fastcgi process on host/port ?)
(fcgi.c.1015) emergency exit: fastcgi: connection-fd: 5
fcgi-fd: 7
the fastcgi process is not running on the host/port you are
connection to. Check your configuration.
If you get ::
(fcgi.c.274) connect delayed: 7
(fcgi.c.289) connect succeeded: 7
everything is fine. The connect() call just was delayed a
little bit and is completly normal.