Embedded C/C++ web server


CivetWeb is a small and easy to use web server. It may be embedded into C/C++ host applications or used as a stand-alone server. See Embedding.md for information on embedding CivetWeb into host applications.

The stand-alone server is self-contained, and does not require any external software to run. Some Windows users may need to install the Visual C++ Redistributable.


On Windows, UNIX and Mac, the CivetWeb stand-alone executable may be started from the command line. Running CivetWeb in a terminal, optionally followed by configuration parameters (CivetWeb [OPTIONS]) or a configuration file name (CivetWeb [config_file_name]), starts the web server.

For UNIX and Mac, CivetWeb does not detach from the terminal. Pressing Ctrl-C keys will stop the server.

On Windows, CivetWeb iconifies itself to the system tray icon when started. Right-clicking on the icon pops up a menu, where it is possible to stop CivetWeb, configure it, or install it as Windows service.

When started without options, the server exposes the local directory at http port 8080. Thus, the easiest way to share a folder on Windows is to copy CivetWeb.exe to this folder, double-click the exe, and launch a browser at http://localhost:8080. Note that ‘localhost’ should be changed to a machine’s name if a folder is accessed from another computer.

When started, CivetWeb first searches for the configuration file. If a configuration file is specified explicitly in the command line, i.e. CivetWeb path_to_config_file, then the specified configuration file is used. Otherwise, CivetWeb will search for the file CivetWeb.conf in the same directory that the executable is located, and use it. This configuration file is optional.

The configuration file is a sequence of lines, each line containing one command line argument name and the corresponding value. Empty lines, and lines beginning with #, are ignored. Here is the example of a CivetWeb.conf file:

document_root c:\www
listening_ports 80,443s
ssl_certificate c:\CivetWeb\ssl_cert.pem

When a configuration file is used, additional command line arguments may override the configuration file settings. All command line arguments must start with -.

For example: The above CivetWeb.conf file is used, and CivetWeb started as CivetWeb -document_root D:\web. Then the D:\web directory will be served as document root, because command line options take priority over the configuration file. The configuration options section below provides a good overview of CivetWeb features.

Note that configuration options on the command line must start with -, but their names are the same as in the config file. All option names are listed in the next section. Thus, the following two setups are equivalent:

# Using command line arguments
$ CivetWeb -listening_ports 1234 -document_root /var/www

# Using config file
$ cat CivetWeb.conf
listening_ports 1234
document_root /var/www
$ CivetWeb

CivetWeb can also be used to modify .htpasswd passwords files:

CivetWeb -A <htpasswd_file> <realm> <user> <passwd>

Configuration Options

Below is a list of configuration options understood by CivetWeb. Every option is followed by it’s default value. If a default value is not present, then the default is empty.

Pattern matching in configuration options

CivetWeb uses shell-like glob patterns for several configuration options, e.g., CGI, SSI and Lua script files are recognized by the file name pattern. Pattern match starts at the beginning of the string, so essentially patterns are prefix patterns. Syntax is as follows:

 **      Matches everything
 *       Matches everything but the slash character ('/')
 ?       Matches any character but the slash character ('/')
 $       Matches the end of the string
 |       Matches if pattern on the left side or the right side matches.

All other characters in the pattern match themselves. Examples:

**.cgi$          Any string that ends with .cgi
/foo             Any string that begins with /foo
**a$|**b$        Any string that ends with a or b

/data/????.css$  Matches css files with 4 letter names in "/data" folder.
/data/*.js$      Matches all js file names in "/data" folder.
/api/*/*.cgi$    Matches "/api/resourcetype/resourcename.cgi"
/*.jpg$|/*.jpeg$ JPG and JPEG files in root folder
**.jpg$|**.jpeg$ JPG and JPEG files anywhere

Options from civetweb.c

The following options are supported in civetweb.c. They can be used for the stand-alone executable as well as for applications embedding CivetWeb. The stand-alone executable supports some additional options: see Options from main.c. The options are explained in alphabetic order - for a quick start, check document_root, listening_ports, error_log_file and (for HTTPS) ssl_certificate.

access_control_allow_headers *

Access-Control-Allow-Headers header field, used for cross-origin resource sharing (CORS) pre-flight requests. See the Wikipedia page on CORS.

If set to an empty string, pre-flights will not allow additional headers. If set to “*”, the pre-flight will allow whatever headers have been requested. If set to a comma separated list of valid HTTP headers, the pre-flight will return exactly this list as allowed headers. If set in any other way, the result is unspecified.

access_control_allow_methods *

Access-Control-Allow-Methods header field, used for cross-origin resource sharing (CORS) pre-flight requests. See the Wikipedia page on CORS.

If set to an empty string, pre-flights will not be supported directly by the server, but scripts may still support pre-flights by handling the OPTIONS method properly. If set to “*”, the pre-flight will allow whatever method has been requested. If set to a comma separated list of valid HTTP methods, the pre-flight will return exactly this list as allowed method. If set in any other way, the result is unspecified.

access_control_allow_origin *

Access-Control-Allow-Origin header field, used for cross-origin resource sharing (CORS). See the Wikipedia page on CORS.


An Access Control List (ACL) allows restrictions to be put on the list of IP addresses which have access to the web server. In the case of the CivetWeb web server, the ACL is a comma separated list of IP subnets, where each subnet is pre-pended by either a - or a + sign. A plus sign means allow, where a minus sign means deny. If a subnet mask is omitted, such as -, this means to deny only that single IP address.

If this value is not set, all accesses are allowed. Otherwise, the default setting is to deny all accesses. On each request the full list is traversed, and the last match wins. Examples:

+,+fe80::/64    deny all accesses, allow and fe80::/64 subnet
                              (The second one is valid only if IPv6 support is enabled)

To learn more about subnet masks, see the Wikipedia page on Subnetwork.


Path to a file for access logs. Either full path, or relative to the current working directory. If absent (default), then accesses are not logged.


Send additional HTTP response header line for every request. The full header line including key and value must be specified, excluding the carriage return line feed.

Example (used as command line option): -additional_header "X-Frame-Options: SAMEORIGIN"

This option can be specified multiple times. All specified header lines will be sent.

allow_index_script_resource no

Index scripts (like index.cgi or index.lua) may have script handled resources.

It this feature is activated, that /some/path/file.ext might be handled by:

  1. /some/path/file.ext (with PATH_INFO=’/’, if ext = cgi)
  2. /some/path/index.lua with mg.request_info.path_info=’/file.ext’
  3. /some/path/index.cgi with PATH_INFO=’/file.ext’
  4. /some/path/index.php with PATH_INFO=’/file.ext’
  5. /some/index.lua with mg.request_info.path_info==’/path/file.ext’
  6. /some/index.cgi with PATH_INFO=’/path/file.ext’
  7. /some/index.php with PATH_INFO=’/path/file.ext’
  8. /index.lua with mg.request_info.path_info==’/some/path/file.ext’
  9. /index.cgi with PATH_INFO=’/some/path/file.ext’
  10. /index.php with PATH_INFO=’/some/path/file.ext’

Note: This example is valid, if the default configuration values for index_files, cgi_pattern and lua_script_pattern are used, and the server is built with CGI and Lua support enabled.

If this feature is not activated, only the first file (/some/path/file.cgi) will be accepted.

Note: This parameter affects only index scripts. A path like /here/script.cgi/handle/this.ext will call /here/script.cgi with PATH_INFO=’/handle/this.ext’, no matter if this option is set to yes or no.

This feature can be used to completely hide the script extension from the URL.

allow_sendfile_call yes

This option can be used to enable or disable the use of the Linux sendfile system call. It is only available for Linux systems and only affecting HTTP (not HTTPS) connections if throttle is not enabled. While using the sendfile call will lead to a performance boost for HTTP connections, this call may be broken for some file systems and some operating system versions.

authentication_domain mydomain.com

Authorization realm used for HTTP digest authentication. This domain is used in the encoding of the .htpasswd authorization files as well. Changing the domain retroactively will render the existing passwords useless.

case_sensitive no

This option can be uset to enable case URLs for Windows servers. It is only available for Windows systems. Windows file systems are not case sensitive, but they still store the file name including case. If this option is set to yes, the comparison for URIs and Windows file names will be case sensitive.


Extra environment variables to be passed to the CGI script in addition to standard ones. The list must be comma-separated list of name=value pairs, like this: VARIABLE1=VALUE1,VARIABLE2=VALUE2.


Path to an executable to use as CGI interpreter for all CGI scripts regardless of the script file extension. If this option is not set (which is the default), CivetWeb looks at first line of a CGI script, shebang line, for an interpreter (not only on Linux and Mac but also for Windows).

For example, if both PHP and Perl CGIs are used, then #!/path/to/php-cgi.exe and #!/path/to/perl.exe must be first lines of the respective CGI scripts. Note that paths should be either full file paths, or file paths relative to the current working directory of the CivetWeb server. If CivetWeb is started by mouse double-click on Windows, the current working directory is the directory where the CivetWeb executable is located.

If all CGIs use the same interpreter, for example they are all PHP, it is more efficient to set cgi_interpreter to the path to php-cgi.exe. The shebang line in the CGI scripts can be omitted in this case. Note that PHP scripts must use php-cgi.exe as executable, not php.exe.


Optional additional arguments passed to a Windows CGI interpreter program.

cgi_pattern **.cgi$|**.pl$|**.php$

All files that match cgi_pattern are treated as CGI files. The default pattern allows CGI files be anywhere. To restrict CGIs to a certain directory, use /path/to/cgi-bin/**.cgi as the pattern. Note that the full file path is matched against the pattern, not the URI.

Depending on the build configuration, additional patterns cgi2_pattern, cgi3_pattern and cgi4_pattern may be available. This allows to use different cgi interpreter programs (cgi2_interpreter, …), environments (cgi2_environment …) and interpreter arguments (cgi2_interpreter_argument, …). The default for all additional CGI file patterns is empty - they are not used unless they are configured explicitly.


Maximum allowed runtime for CGI scripts. CGI processes are terminated by the server after this time. The default is “no timeout”, so scripts may run or block for undefined time.

cgi_buffering yes

Allow buffering response of CGI program before sending to the client. When buffering is enabled content created by CGI scripts is collected in a buffer and forwarded to the client in larger blocks, improving efficiency. If partial content has to be sent to the client, try setting cgi_buffering to no, allow_sendfile_call to no and tcp_nodelay to 1. This will cost some performance, but not guarantee there is no buffering between CGI program and client code, since intermediate proxies or browsers may also buffer data.

decode_query_string no

URL decode all query strings in the server. If you set this option to yes, all callbacks and scripts will only see the already decoded query string. If this option is set to no, all callbacks and scripts have to decode the query strings on their own, if they need to. Note that setting this option to yes is not compatible with submitting form data using “GET” requests (but it is compatible with submitting form data using the “POST” method; using “POST” is recommended for most use cases).

decode_url yes

The server should decode the URL, according to the HTTP standard. This means, http://mydomain.com/this%20file.txt will be decoded to this file.txt (%20 corresponds to the URL encoding of the space character). Set this option to no only if you are using callbacks exclusively and need access to the encoded URLs.

document_root .

A directory to serve. By default, the current working directory is served. The current directory is commonly referenced as dot (.). It is recommended to use an absolute path for document_root, in order to avoid accidentally serving the wrong directory.

enable_auth_domain_check yes

When using absolute URLs, verify the host is identical to the authentication_domain. If enabled, requests to absolute URLs will only be processed if they are directed to the domain. If disabled, absolute URLs to any host will be accepted.

enable_directory_listing yes

Enable directory listing, either yes or no.

enable_http2 no

Enable HTTP2 protocol. Note: This option is only available, if the server has been compiled with the USE_HTTP2 define. The CivetWeb server supports only a subset of all HTTP2 features.

enable_keep_alive no

Enable connection keep alive, either yes or no.

Allows clients to reuse TCP connection for subsequent HTTP requests, which improves performance. For this to work when using request handlers it is important to add the correct Content-Length HTTP header for each request. If this is forgotten the client will time out.

Note: If you set keep_alive to yes, you should set keep_alive_timeout_ms to some value > 0 (e.g. 500). If you set keep_alive to no, you should set keep_alive_timeout_ms to 0. Currently, this is done as a default value, but this configuration is redundant. In a future version, the keep_alive configuration option might be removed and automatically set to yes if a timeout > 0 is set.

enable_webdav no

Set this configuration option to yes to handle WebDAV specific HTTP methods: PROPFIND, PROPPATCH, LOCK, UNLOCK, MOVE, COPY. These methods are not allowed if the configuration option is set to no.

enable_websocket_ping_pong no

If this configuration value is set to yes, the server will send a websocket PING message to a websocket client, once the timeout set by websocket_timeout_ms expires. Clients (Web browsers) supporting this feature will reply with a PONG message.

If this configuration value is set to no, the websocket server will close the connection, once the timeout expires.

Note: This configuration value only exists, if the server has been built with websocket support enabled.


Path to a file for error logs. Either full path, or relative to the current working directory. If absent (default), then errors are not logged.


This option may be used to specify a directory for user defined error pages. To specify a directory, make sure the name ends with a backslash (Windows) or slash (Linux, MacOS, …). The error pages may be specified for an individual http status code (e.g., 404 - page requested by the client not found), a group of http status codes (e.g., 4xx - all client errors) or all errors. The corresponding error pages must be called error404.ext, error4xx.ext or error.ext, whereas the file extension may be one of the extensions specified for the index_files option. See the Wikipedia page on HTTP status codes.


Extra mime types, in the form extension1=type1,exten-sion2=type2,.... See the Wikipedia page on Internet media types. Extension must include a leading dot. Example: .cpp=plain/text,.java=plain/text


Path to a global passwords file, either full path or relative to the current working directory. If set, per-directory .htpasswd files are ignored, and all requests are authorized against that file.

The file has to include the realm set through authentication_domain and the password in digest format:


Password files may be generated using CivetWeb -A as explained above, or online tools e.g. this generator.


A pattern for the files to hide. Files that match the pattern will not show up in directory listing and return 404 Not Found if requested. Pattern must be for a file name only, not including directory names. Example:

CivetWeb -hide_files_patterns secret.txt|**.hide

Note: hide_file_patterns uses the pattern described above. If you want to hide all files with a certain extension, make sure to use **.extension (not just *.extension).

index_files index.xhtml,index.html,index.htm,index.cgi,index.shtml,index.php

Comma-separated list of files to be treated as directory index files. If more than one matching file is present in a directory, the one listed to the left is used as a directory index.

In case built-in Lua support has been enabled, index.lp,index.lsp,index.lua are additional default index files, ordered before index.cgi.

keep_alive_timeout_ms 500 or 0

Idle timeout between two requests in one keep-alive connection. If keep alive is enabled, multiple requests using the same connection are possible. This reduces the overhead for opening and closing connections when loading several resources from one server, but it also blocks one port and one thread at the server during the lifetime of this connection. Unfortunately, browsers do not close the keep-alive connection after loading all resources required to show a website. The server closes a keep-alive connection, if there is no additional request from the client during this timeout.

Note: if enable_keep_alive is set to no the value of keep_alive_timeout_ms should be set to 0, if enable_keep_alive is set to yes, the value of keep_alive_timeout_ms must be >0. Currently keep_alive_timeout_ms is ignored if enable_keep_alive is no, but future versions may drop the enable_keep_alive configuration value and automatically use keep-alive if keep_alive_timeout_ms is not 0.


Set TCP socket linger timeout before closing sockets (SO_LINGER option). The configured value is a timeout in milliseconds. Setting the value to 0 will yield in abortive close (if the socket is closed from the server side). Setting the value to -1 will turn off linger. If the value is not set (or set to -2), CivetWeb will not set the linger option at all.

Note: For consistency with other timeout configurations, the value is configured in milliseconds. However, the TCP socket layer usually only offers a timeout in seconds, so the value should be an integer multiple of 1000.

listening_ports 8080

Comma-separated list of ports to listen on. If the port is SSL, a letter s must be appended, for example, 80,443s will open port 80 and port 443, and connections on port 443 will be SSL-ed. For non-SSL ports, it is allowed to append letter r, meaning ‘redirect’. Redirect ports will redirect all their traffic to the first configured SSL port. For example, if listening_ports is 80r,443s, then all HTTP traffic coming at port 80 will be redirected to HTTPS port 443.

It is possible to specify an IP address to bind to. In this case, an IP address and a colon must be pre-pended to the port number. For example, to bind to a loopback interface on port 80 and to all interfaces on HTTPS port 443, use,443s.

If the server is built with IPv6 support, [::]:8080 can be used to listen to IPv6 connections to port 8080. IPv6 addresses of network interfaces can be specified as well, e.g. [::1]:8080 for the IPv6 loopback interface.

all interfaces, both IPv4 and IPv6, use either the configuration 80,[::]:80 (create one socket for IPv4 and one for IPv6 only), or +80 (create one socket for both, IPv4 and IPv6). The + notation to use IPv4 and IPv6 will only work if no network interface is specified. Depending on your operating system version and IPv6 network environment, some configurations might not work as expected, so you have to test to find the configuration most suitable for your needs. In case +80 does not work for your environment, you need to use 80,[::]:80.

It is possible to use network interface addresses (e.g.,, [2001:0db8::1234]:80). To get a list of available network interface addresses, use ipconfig (in a cmd window in Windows) or ifconfig (in a Linux shell). Alternatively, you could use the hostname for an interface. Check the hosts file of your operating system for a proper hostname (for Windows, usually found in C:\Windows\System32\drivers\etc\, for most Linux distributions: /etc/hosts). E.g., to bind the IPv6 local host, you could use ip6-localhost:80. This translates to [::1]:80. Beside the hosts file, there are several other name resolution services. Using your hostname might bind you to the localhost or an external interface. You could also try hostname.local, if the proper network services are installed (Zeroconf, mDNS, Bonjour, Avahi). When using a hostname, you need to test in your particular network environment - in some cases, you might need to resort to a fixed IP address.

If you want to use an ephemeral port (i.e. let the operating system choose a port number), use 0 for the port number. This will make it necessary to communicate the port number to clients via other means, for example mDNS (Zeroconf, Bonjour, Avahi).

In case the server has been built with the USE_X_DOM_SOCKET option set, it can listen to unix domain sockets as well. They are specified by a lower case x followed by the domain socket path, e.g. x/tmp/sockname. Domain sockets do not require a port number, always use HTTP (not HTTPS) and never redirect. Thus : is not allowed, while r or s at the end of the configuration is interpreted as part of the domain socket path. The domain sochet path must be a valid path to a non-existing file on a Unix/Linux system. The CivetWeb process needs write/create access rights to create the domain socket in the Unix/Linux file system. Use only alphanumerical characters, underscore and / in a domain socket path (in particular, ,;: must be avoided).

All socket/protocol types may be combined, separated by ,. E.g.:,[::1]:80,x/tmp/sockname will listen to localhost http connections using IPv4, IPv6 and the domain socket /tmp/sockname.


Run a Lua script in the background, independent from any connection. The script is started before network access to the server is available. It can be used to prepare the document root (e.g., update files, compress files, …), check for external resources, remove old log files, etc.

The script can define callbacks to be notified when the server starts or stops. Furthermore, it can be used for log filtering or formatting. The Lua state remains open until the server is stopped.

For a detailed descriotion of available Lua callbacks see section “Lua background script” below.


Can add dynamic parameters to background script. Parameters mapped into ‘mg.params’ as table. Example: paramName1=paramValue1,paramName2=2


This configuration option can be used to specify a Lua script file, which is executed before the actual web page script (Lua script, Lua server page or Lua websocket). It can be used to modify the Lua environment of all web page scripts, e.g., by loading additional libraries or defining functions required by all scripts. It may be used to achieve backward compatibility by defining obsolete functions as well.

lua_script_pattern "**.lua$

A pattern for files that are interpreted as Lua scripts by the server. In contrast to Lua server pages, Lua scripts use plain Lua syntax. An example can be found in the test directory.

lua_server_page_pattern **.lp$|**.lsp$

Files matching this pattern are treated as Lua server pages. In contrast to Lua scripts, the content of a Lua server pages is delivered directly to the client. Lua script parts are delimited from the standard content by including them between <? and ?> tags. An example can be found in the test directory.

lua_websocket_pattern "**.lua$

A pattern for websocket script files that are interpreted as Lua scripts by the server.

max_request_size 16384

Size limit for HTTP request headers and header data returned from CGI scripts, in Bytes. A buffer of the configured size is pre allocated for every worker thread. max_request_size limits the HTTP header, including query string and cookies, but it does not affect the HTTP body length. The server has to read the entire header from a client or from a CGI script, before it is able to process it. In case the header is longer than max_request_size, the request is considered as invalid or as DoS attack. The configuration value is approximate, the real limit might be a few bytes off. The minimum is 1024 (1 kB).

num_threads 50

Number of worker threads. CivetWeb handles each incoming connection in a separate thread. Therefore, the value of this option is effectively the number of concurrent HTTP connections CivetWeb can handle.

If there are more simultaneous requests (connection attempts), they are queued. Every connection attempt first needs to be accepted (up to a limit of listen_backlog waiting connections). Then it is accepted and queued for the next available worker thread (up to a limit of connection_queue). Finally a worker thread handles all requests received in a connection (up to num_threads).

In case the clients are web browsers, it is recommended to use num_threads of at least 5, since browsers often establish multiple connections to load a single web page, including all linked documents (CSS, JavaScript, images, …).

listen_backlog 200

Maximum number of connections waiting to be accepted by the server operating system. Internally, this parameter is passed to the “listen” socket/system call.

connection_queue 20

Maximum number of accepted connections waiting to be dispatched by a worker thread.


Comma separated list of URI=PATH pairs, specifying that given URIs must be protected with password files specified by PATH. All Paths must be full file paths.


Passwords file for PUT and DELETE requests. Without a password file, it will not be possible to PUT new files to the server or DELETE existing ones. PUT and DELETE requests might still be handled by Lua scripts and CGI paged.

request_timeout_ms 30000

Timeout for network read and network write operations, in milliseconds. If a client intends to keep long-running connection, either increase this value or (better) use keep-alive messages.


Switch to given user credentials after startup. Usually, this option is required when CivetWeb needs to bind on privileged ports on UNIX. To do that, CivetWeb needs to be started as root. From a security point of view, running as root is not advisable, therefore this option can be used to drop privileges. Example:

civetweb -listening_ports 80 -run_as_user webserver

ssi_pattern **.shtml$|**.shtm$

All files that match ssi_pattern are treated as Server Side Includes (SSI).

SSI is a simple interpreted server-side scripting language which is most commonly used to include the contents of another file in a web page. It can be useful when it is desirable to include a common piece of code throughout a website, for example, headers and footers.

In order for a webpage to recognize an SSI-enabled HTML file, the filename should end with a special extension, by default the extension should be either .shtml or .shtm. These extensions may be changed using the ssi_pattern option.

Unknown SSI directives are silently ignored by CivetWeb. Currently, two SSI directives are supported, <!--#include ...> and <!--#exec "command">. Note that the <!--#include ...> directive supports three path specifications:

<!--#include virtual="path">  Path is relative to web server root
<!--#include abspath="path">  Path is absolute or relative to
                              web server working dir
<!--#include file="path">,    Path is relative to current document
<!--#include "path">

The include directive may be used to include the contents of a file or the result of running a CGI script. The exec directive is used to execute a command on a server, and show the output that would have been printed to stdout (the terminal window) otherwise. Example:

<!--#exec "ls -l" -->

For more information on Server Side Includes, take a look at the Wikipedia: Server Side Includes


Path to a .pem file containing trusted certificates. The file may contain more than one certificate.


Name of a directory containing trusted CA certificates. Each file in the directory must contain only a single CA certificate. The files must be named by the subject name’s hash and an extension of “.0”. If there is more than one certificate with the same subject name they should have extensions “.0”, “.1”, “.2” and so on respectively.

ssl_cache_timeout -1

Allow caching of SSL/TLS sessions, so HTTPS connection from the same client to the same server can be established faster. A configuration value >0 activates session caching. The configuration value is the maximum lifetime of a cached session in seconds. The default is to deactivated session caching.


Path to the SSL certificate file. This option is only required when at least one of the listening\_ports is SSL. The file must be in PEM format, and it must have both, private key and certificate, see for example ssl_cert.pem A description how to create a certificate can be found in doc/OpenSSL.md


Path to an SSL certificate chain file. As a default, the ssl_certificate file is used.


List of ciphers to present to the client. Entries should be separated by colons, commas or spaces.

ALL           All available ciphers
ALL:!eNULL    All ciphers excluding NULL ciphers
AES128:!MD5   AES 128 with digests other than MD5

See this entry in OpenSSL documentation for full list of options and additional examples. The OpenSSL cipher string uses different cipher names than IANA (see this mapping).

In case CivetWeb is built with a TLS library other than OpenSSL (e.g., mbedTLS), the cipher names may be different.

ssl_default_verify_paths yes

Loads default trusted certificates locations set at openssl compile time.

ssl_protocol_version 4

Sets the minimal accepted version of SSL/TLS protocol according to the table:

Protocols Value
SSL2+SSL3+TLS1.0+TLS1.1+TLS1.2+TLS1.3 0
SSL3+TLS1.0+TLS1.1+TLS1.2+TLS1.3 1
TLS1.0+TLS1.1+TLS1.2+TLS1.3 2
TLS1.1+TLS1.2+TLS1.3 3
TLS1.2+TLS1.3 4
TLS1.3 5

TLS version 1.3 is only available if you are using an up-to-date TLS libary. The default setting has been changed from 0 to 4 in CivetWeb 1.14.

ssl_short_trust no

Enables the use of short lived certificates. This will allow for the certificates and keys specified in ssl_certificate, ssl_ca_file and ssl_ca_path to be exchanged and reloaded while the server is running.

In an automated environment it is advised to first write the new pem file to a different filename and then to rename it to the configured pem file name to increase performance while swapping the certificate.

Disk IO performance can be improved when keeping the certificates and keys stored on a tmpfs (linux) on a system with very high throughput.

ssl_verify_depth 9

Sets maximum depth of certificate chain. If client’s certificate chain is longer than the depth set here connection is refused.

ssl_verify_peer no

Enable client’s certificate verification by the server.


Set the Cache-Control header of static files responses. The string value will be used directly.

E.g. this config:

static_file_cache_control no-cache, max-age=31536000

Will result in this header being added:

Cache-Control: no-cache, max-age=31536000

This will take precedence over the static_file_max_age option.

static_file_max_age 3600

Set the maximum time (in seconds) a cache may store a static files.

This option will set the Cache-Control: max-age value for static files. Dynamically generated content, i.e., content created by a script or callback, must send cache control headers by themselves.

A value >0 corresponds to a maximum allowed caching time in seconds. This value should not exceed one year (RFC 2616, Section 14.21). A value of 0 will send “do not cache at all” headers for all static files. For values <0 and values >31622400 (366 days), the behaviour is undefined.


Set the Strict-Transport-Security header, and set the max-age value. This instructs web browsers to interact with the server only using HTTPS, never by HTTP. If set, it will be sent for every request handled directly by the server, except scripts (CGI, Lua, ..) and callbacks. They must send HTTP headers on their own.

The time is specified in seconds. If this configuration is not set, or set to -1, no Strict-Transport-Security header will be sent. For values <-1 and values >31622400, the behaviour is undefined.

tcp_nodelay 0

Enable TCP_NODELAY socket option on client connections.

If set the socket option will disable Nagle’s algorithm on the connection which means that packets will be sent as soon as possible instead of waiting for a full buffer or timeout to occur.

0    Keep the default: Nagel's algorithm enabled
1    Disable Nagel's algorithm for all sockets


Limit download speed for clients. throttle is a comma-separated list of key=value pairs, where key could be:

*                   limit speed for all connections
x.x.x.x/mask        limit speed for specified subnet
[IPv6-addr]/mask    limit speed for specified IPv6 subnet (needs square brackets)
uri_prefix_pattern  limit speed for given URIs

The value is a floating-point number of bytes per second, optionally followed by a k or m character, meaning kilobytes and megabytes respectively. A limit of 0 means unlimited rate. The last matching rule wins. Examples:

*=1k,   limit all accesses to 1 kilobyte per second,
                    but give connections the from subnet
                    unlimited speed

/downloads/=5k      limit accesses to all URIs in `/downloads/` to
                    5 kilobytes per second. All other accesses are unlimited


Comma-separated list of URL rewrites in the form of uri_pattern=file_or_directory_path. When CivetWeb receives any request, it constructs the file name to show by combining document_root and the URI. However, if the rewrite option is used and uri_pattern matches the requested URI, then document_root is ignored. Instead, file_or_directory_path is used, which should be a full path name or a path relative to the web server’s current working directory. Note that uri_pattern, as all CivetWeb patterns, is a prefix pattern.

This makes it possible to serve many directories outside from document_root, redirect all requests to scripts, and do other tricky things. For example, to redirect all accesses to .doc files to a special script, do:

CivetWeb -url_rewrite_patterns **.doc$=/path/to/cgi-bin/handle_doc.cgi

Or, to imitate support for user home directories, do:

CivetWeb -url_rewrite_patterns /~joe/=/home/joe/,/~bill=/home/bill/


In case CivetWeb is built with Lua and websocket support, Lua scripts may be used for websockets as well. Since websockets use a different URL scheme (ws, wss) than other http pages (http, https), the Lua scripts used for websockets may also be served from a different directory. By default, the document_root is used as websocket_root as well.


Timeout for network read and network write operations for websockets, WS(S), in milliseconds. If this value is not set, the value of request_timeout_ms is used for HTTP(S) as well as for WS(S). In case websocket_timeout_ms is set, HTTP(S) and WS(S) can use different timeouts.

Note: This configuration value only exists, if the server has been built with websocket support enabled.

Options from main.c

The following options are supported in main.c, the additional source file for the stand-alone executable. These options are not supported by other applications embedding civetweb.c, unless they are added to the embedding application.


Use the configured string as a server name. For Windows, this will be shown as the window title.


For Windows, show this icon file in the systray, replacing the CivetWeb standard icon. This option has no effect for Linux.


For Windows, use this website as a link in the systray, replacing the default link for CivetWeb.

hide_tray no

For Windows: Do not show a tray icon. May be yes (hide) or no (show, default).

daemonize no

This option is only available for Linux, if the server has been build with the DAEMONIZE compile options. Call (deprecated) daemon() BSD function to detach the server process from the controlling terminal and run it in the background as a system daemon.


Option to load an additional configuration file, specifying an additional domain to host. To add multiple additional domains, use the add_domain option multiple times with one configuration file for each domain. This option is available for Windows and Linux operating systems.

Internally, the options are passed to the mg_start_domain API function. If you are not using main.c, you need to call this API function to activate and additional domain.

Every domain configuration file may contain a subset of the options available for the main server configuration files, with some exceptions. Some configurations are per server while others are available for each domain.

All port, socket, process and thread specific parameters are per server: allow_sendfile_call, case_sensitive, connection_queue, decode_url, enable_http2, enable_keep_alive, enable_websocket_ping_pong, keep_alive_timeout_ms, linger_timeout_ms, listen_backlog, listening_ports, lua_background_script, lua_background_script_params, max_request_size, num_threads, request_timeout_ms, run_as_user, tcp_nodelay, throttle, websocket_timeout_ms + all options from main.c.

All other options can be set per domain. In particular authentication_domain, document_root and (for HTTPS) ssl_certificate must be set for each additional domain.

While some options like error_log_file are per domain, the setting of the initial (main) domain may be used if the server could not determine the correct domain for a specific request.


Lua Scripts and Lua Server Pages

Pre-built Windows and Mac CivetWeb binaries have built-in Lua scripting support as well as support for Lua Server Pages.

Lua scripts (default extension: *.lua) use plain Lua syntax. The body of the script file is not sent directly to the client, the Lua script must send header and content of the web page by calling the function mg.write(text).

Lua Server Pages (default extensions: *.lsp, *.lp) are html pages containing script elements similar to PHP, using the Lua programming language instead of PHP. Lua script elements must be enclosed in <? ?> blocks, and can appear anywhere on the page. Furthermore, Lua Server Pages offer the opportunity to insert the content of a variable by enclosing the Lua variable name in <?= ?> blocks, similar to PHP. For example, to print the current weekday name and the URI of the current page, one can write:

  <span>Today is:</span>
  <? mg.write(os.date("%A")) ?>
  URI is <?=mg.request_info.uri?>

From version 1.11, CivetWeb supports “Kepler Syntax” in addition to the traditional Lua pages syntax of CivetWeb. Kepler Syntax uses <?lua ?> or <% %> blocks for script elements (corresponding to <? ?> above) and <?lua= ?> or <%= %> for variable content (corresponding to <?= ?>).

   <% for key, value in pairs(mg.request_info) do %>
   <li> <%= key %>: <%= value %> </li>
   <% end %>

Currently the extended “Kepler Syntax” is available only for HTML (see note on HTTP headers below).

Lua is known for it’s speed and small size. The default Lua version for CivetWeb is Lua 5.2.4. The documentation for it can be found in the Lua 5.2 reference manual. However, CivetWeb can be built with Lua 5.1, 5.2, 5.3, 5.4 (currently pre-release) and LuaJIT.

Note that this example uses function mg.write(), which sends data to the web client. Using mg.write() is the way to generate web content from inside Lua code. In addition to mg.write(), all standard Lua library functions are accessible from the Lua code (please check the reference manual for details). Lua functions working on files (e.g., io.open) use a path relative to the working path of the CivetWeb process. The web server content is located in the path mg.document_root. Information on the request is available in the mg.request_info object, like the request method, all HTTP headers, etcetera.

page2.lua is an example for a plain Lua script.

page2.lp is an example for a Lua Server Page.

page4kepler.lp is a Lua Server Page showing “Kepler Syntax” in addition to traditional CivetWeb Lua Server Pages syntax.

These examples show the content of the mg.request_info object as the page content. Please refer to struct mg_request_info definition in CivetWeb.h to see additional information on the elements of the mg.request_info object.

CivetWeb also provides access to the SQlite3 database through the LuaSQLite3 interface in Lua. Examples are given in page.lua and page.lp.

CivetWeb exports the following functions to Lua:

mg (table):

mg.read()                   -- reads a chunk from POST data, returns it as a string
mg.write(str)               -- writes string to the client
mg.cry(str)                 -- logs error string to stderr
mg.include(filename, [pathtype]) -- include another Lua Page file (Lua Pages only)
                            -- pathtype can be "abs", "rel"/"file" or "virt[ual]"
                            -- like defined for SSI #include
mg.redirect(uri)            -- redirect to internal URI
mg.onerror(msg)             -- error handler, can be overridden
mg.auth_domain              -- a string that holds the HTTP authentication domain
mg.document_root            -- a string that holds the document root directory
mg.lua_type                 -- a string that holds the lua script type
mg.system                   -- a string that holds the operating system name
mg.version                  -- a string that holds CivetWeb version
mg.get_cookie(str, cookie)  -- extract cookie from a string
mg.get_info(infotype)       -- get server status information
mg.get_mime_type(filename)  -- get MIME type of a file
mg.get_option(name)         -- get configuration option value from name
mg.get_response_code_text(n)-- get response code text for n, nil otherwise
mg.get_var(str, varname, [occurance])  -- extract the first occurance of variable from (query) string
                            --     otherwise the nth occurance if supplied, nil if not found
mg.send_file(filename)      -- send a file, including all required HTTP headers
mg.send_file_body(filename) -- send a file, excluding HTTP headers
mg.send_http_error(n,str)   -- send http error code n with string body
mg.send_http_ok(mime,body)  -- send http 200 OK with content-type mime and string body
mg.send_http_ok(mime,length)-- send http 200 OK with content-type mime and integer content-length length
mg.send_http_redirect(url,n)-- redirect to url with status code n
mg.split_form_data(form)    -- returns a table of the split form data
mg.url_encode(str)          -- URL encode a string
mg.url_decode(str, [form])  -- URL decode a string. If form=true, replace + by space.
mg.base64_encode(str)       -- BASE64 encode a string
mg.base64_decode(str)       -- BASE64 decode a string
mg.md5(str)                 -- return the MD5 hash of a string
mg.keep_alive(bool)         -- allow/forbid to use http keep-alive for this request
mg.time([bool])             -- get the current unix timestamp with milliseconds
                            --     if bool is true then it is the time since startup
mg.trace(n,message,...)     -- trace level n messages into tracefile
mg.uuid()                   -- generate a uuid
mg.random()                 -- get a random floating point number
mg.request_info             -- a table with the following request information
     .content_length        -- Request content-length as a float
     .content_type          -- Request content-type, nil otherwise
     .request_link          -- Requested link
     .request_uri           -- Request URI
     .uri                   -- Local request URI
     .path_info             -- Request URI, nil otherwise
     .status                -- Request status code, nil otherwise
     .remote_addr           -- IP address of the client as string
     .remote_port           -- remote port number
     .server_port           -- server port number
     .request_method        -- HTTP method (e.g.: GET, POST)
     .http_version          -- HTTP protocol version (e.g.: 1.1)
     .http_headers          -- Table of HTTP headers
     .num_headers           -- Number of headers
     .query_string          -- query string if present, nil otherwise
     .script_name           -- name of the Lua script, nil otherwise
     .https                 -- true if accessed by https://, false otherwise
     .remote_user           -- user name if authenticated, nil otherwise
     .auth_type             -- Digest
     .client_cert           -- Table with ssl certificate infomation
          .subject          -- Certificate subject
          .issuer           -- Certificate issuer
          .serial           -- Certificate serial number
          .finger           -- Certificate finger

If websocket and timers support is enabled then the following is also available:

mg.set_timeout(fn,delay,[interval])  -- call function after delay at an interval
mg.set_interval(fn,delay,[interval]) -- call function after delay at an interval
mg.websocket_root                    -- a string that holds the websocket root

connect (function):

-- Connect to the remote TCP server. This function is an implementation
-- of simple socket interface. It returns a socket object with three
-- methods: send, recv, close, which are synchronous (blocking).
-- connect() throws an exception on connection error.
-- use_ssl is not implemented.
connect(host, port, use_ssl)

-- Example of using connect() interface:
local host = 'www.example.com'  -- IP address or domain name
local ok, sock = pcall(connect, host, 80, 0)
if ok then
  sock:send('GET / HTTP/1.0\r\n' ..
            'Host: ' .. host .. '\r\n\r\n')
  local reply = sock:recv()
  -- reply now contains the web page http://www.example.com/

All filename arguments are either absolute or relative to the CivetWeb working directory (not the document root or the Lua script/page file).

To serve a Lua Page, CivetWeb creates a Lua context. That context is used for all Lua blocks within the page. That means, all Lua blocks on the same page share the same context. If one block defines a variable, for example, that variable is visible in all blocks that follow.

Important note on HTTP headers:

Lua scripts MUST send HTTP headers themselves, e.g.:

mg.write('HTTP/1.0 200 OK\r\nContent-Type: text/html\r\n\r\n')

Lua Server Pages CAN send HTTP reply headers, like this:

HTTP/1.0 200 OK
Content-Type: text/html

  ... the rest of the web page ...

or using Lua code:

<? mg.write('HTTP/1.0 200 OK\r\nContent-Type: text/html\r\n\r\n') ?>
  ... the rest of the web page ...

or Lua Server Pages generating HTML content MAY skip the HTTP header lines. In this case, CivetWeb automatically creates a “200 OK”/”Content-Type: text/html” reply header. In this case, the document must start with “<!DOCTYPE html>” or “<html”.

Currently the extended “Kepler Syntax” is available only for text/html pages not sending their own HTTP headers. Thus, “Kepler Syntax” can only be used for HTML pages, while traditional CivetWeb syntax can be used to send a content-type header and generate any kind of file.

Websockets for Lua

CivetWeb offers support for websockets in Lua as well. In contrast to plain Lua scripts and Lua server pages, Lua websocket scripts are shared by all clients.

Lua websocket scripts must define the following functions: ready(arg) – called after a connection has been established data(arg) – called when the server receives data from the client close(arg) – called when a websocket connection is closed All function are called with one argument of type table with at least one field “client” to identify the client. When “open” is called, the argument table additionally contains the “request_info” table as defined above. For the “data” handler, an additional field “data” is available. The functions “open”, “ready” and “data” must return true in order to keep the connection open.

Lua websocket pages do support single shot (timeout) and interval timers.

An example is shown in websocket.lua.

Lua background script

The Lua background script is loaded when the server is starting, before any client is able to connect. It can be used for preparation and maintenance tasks, e.g., for preparing the web contents, cleaning log files, etc.

The Name of the script file including path is configured as lua_background_script. Additional parameters can be supplied using lua_background_script_params.

The background script is loaded before the server is ready to start. It may return a boolean value. If “false” in returned, the server will not be started. Since the server is not fully initialized when the script is loaded, some features of the “mg” library are not available yet. Use the “start()” callbacks function instead.

A Lua background script may define the following functions: start() – called wnen the server is started stop() – called when the server is stopped log(req, res) – called when an access log entry is created

The return values of start and stop are ignored. The start callback can be used to create timers.

The optional function log may be used to filter or format access log file entries. The request_info table is supplied as first argument (content of this table: see above). The second argument is the request processing result. It contains the number of bytes read and written (incl. header information), the processing_time in seconds, the protocol (“http”, “https”, “ws” or “wss”). For internally generated response and response generated using the mg_response_*() API, it will contain the http status code and a the response http_headers table (CGI response will not have all headers).

The function can return a boolean value: true if the entry should be logged or false if not. Alternatively it can return a string: this will be used as log message (empty strings will not be logged).

See example Lua script : background.lua.

Using CGI

Unlike some other web servers, CivetWeb does not require CGI scripts to be located in a special directory. CGI scripts files are recognized by the file name pattern and can be anywhere.

When using CGI, make sure your CGI file names match the cgi\_pattern parameter configured for the server. Furthermore, you must either configure a cgi\_interpreter to be used for all CGI scripts, or all scripts must start with #! followed by the CGI interpreter executable, e.g.: #!/path/to/perl.exe or #!/bin/sh.

See cgi\_pattern and cgi\_interpreter for more details.

It is possible to disable CGI completely by building the server with the NO\_CGI define. Setting this define is required for operating systems not supporting fork/exec or CreateProcess (since CGI is based on creating child processes, it will not be available on such operating systems for principle reasons).

Every CGI request will spawn a new child process. Data sent from the HTTP client to the server is passed to stdin of the child process, while data written to stdout by the child process is sent back to the HTTP client.

In case a CGI script cannot handle a particular request, it might write a short error message to stderr instead of writing to stdout. This error message is added to the server error log.

A script should not write to stderr after writing a reply header to stdout. In case CGI libraries are writing to stderr (e.g., for logging/debugging), the CGI script should redirect stderr to a user defined log file at the beginning of the script.


Common Problems

  • PHP doesn’t work - getting empty page, or ‘File not found’ error. The reason for that is wrong paths to the interpreter. Remember that with PHP, the correct interpreter is php-cgi.exe (php-cgi on UNIX). Solution: specify the full path to the PHP interpreter, e.g.: CivetWeb -cgi_interpreter /full/path/to/php-cgi

  • php-cgi is unavailable, for example on Mac OS X. As long as the php binary is installed, you can run CGI programs in command line mode (see the example below). Note that in this mode, $_GET and friends will be unavailable, and you’ll have to parse the query string manually using parse_str and the QUERY_STRING environmental variable.

      echo "Content-Type: text/html\r\n\r\n";
      echo "Hello World!\n";
  • CivetWeb fails to start. If CivetWeb exits immediately when started, this usually indicates a syntax error in the configuration file (named civetweb.conf by default) or the command-line arguments. Syntax checking is omitted from CivetWeb to keep its size low. However, the Manual should be of help. Note: the syntax changes from time to time, so updating the config file might be necessary after executable update. Try to use the error_log_file option for details.

  • Embedding with OpenSSL on Windows might fail because of calling convention. To force CivetWeb to use __stdcall convention, add /Gz compilation flag in Visual Studio compiler.