Yaws

YAWS.CONF(5) User Commands YAWS.CONF(5)

NAME
/etc/yaws/yaws.conf - Configuration file for the Yaws web server

DESCRIPTION
Yaws is fast lightweight web server. It reads a configuration file
called yaws.conf to control its operations. The configuration contains
two distinct parts: a global part which affects all the virtual hosts
and a server part where options for each virtual host is supplied.

GLOBAL PART
logdir = [+]Directory
All Yaws logs will be written to files in this directory. If
specified with +, Yaws will attempt to create the directory if
it does not exist. There are several different log files written
by Yaws:

report.log - this is a text file that contains all error logger
printouts from Yaws.

<Host>.access - for each virtual host served by Yaws, a file
<Host>.access will be written that contains an access log in
NCSA combined/XLF/ELF log format. (See http://www.w3.org/TR/WD-
logfile.html for more details on Extended Log File Format.)

<Host>.auth - for each virtual host served by Yaws, a file
<Host>.auth will be written which contains all http auth related
messages.

trace_<YYYYMMDD_hhmmss> - Trace files are written in this subdi‐
rectory, suffixed by the creation date.

trace.<Pid>.http - this file contains the HTTP trace if
that is enabled, where <Pid> is the process id handling the
TCP connection.

trace.<Pid>.traffic - this file contains the traffic trace
if that is enabled, where <Pid> is the process id handling
the TCP connection.

Note that <Host>.access and <Host>.auth files will be used only
if the directive logger_mod is not set or set to yaws_log. The
default value for logdir is "."

ebin_dir = Directory
This directive adds Directory to the Erlang search path. It is
possible to have several of these commands in the configuration
file. The default value is "yaws_dir"/examples/ebin

src_dir = Directory
This directive defines a Directory as a source directory. Yaws
will compile all erlang modules found in this directory and all
its subdirectories. The compilation occurs when the configura‐
tion is loaded or reloaded. The include_dir directives are used
to search for includes files. Multiple src_dir directives may be
used. There is no such directory configured by default.

id = String
It is possible to run multiple Yaws servers on the same machine.
We use the id of a Yaws server to control it using the different
control commands such as:

# /usr/local/bin/yaws --id foobar --stop

To stop the Yaws server with id "foobar". Each Yaws server will
write its internal data into a file called $HOME/.yaws/yaws/ID
where ID is the identity of the server. Yaws also creates a file
called $HOME/.yaws/yaws/ID/CTL which contains the port number
where the server is listening for control commands. The default
id is "default".

server_signature = String
This directive sets the "Server: " output header to the custom
value. The default value is "yaws/%VSN%, Yet Another Web
Server".

include_dir = Directory
This directive adds Directory to the path of directories where
the Erlang compiler searches for include files. We need to use
this if we want to include .hrl files in our Yaws Erlang code.
It is possible to have several of these commands in the configu‐
ration file. The default value is "yaws_dir"/examples/include.

max_num_cached_files = Integer
Yaws will cache small files such as commonly accessed GIF images
in RAM. This directive sets a maximum number on the number of
cached files. The default value is 400.

max_num_cached_bytes = Integer
This directive controls the total amount of RAM which can maxi‐
mally be used for cached RAM files. The default value is
1000000, 1 megabyte.

max_size_cached_file = Integer
This directive sets a maximum size on the files that are RAM
cached by Yaws. The default value is 8000, 8 kBytes.

cache_refresh_secs = Integer
The RAM cache is used to serve pages that sit in the cache. An
entry sits in cache at most cache_refresh_secs number of sec‐
onds. The default is 30. This means that when the content is up‐
dated under the docroot, that change doesn't show until 30 sec‐
onds have passed. While developing a Yaws site, it may be conve‐
nient to set this value to 0. If the debug flag (-d) is passed
to the Yaws start script, this value is automatically set to 0.

trace = false | traffic | http
This enables traffic or http tracing. Tracing is also possible
to enable with a command line flag to Yaws. Default is false.

auth_log = true | false
Deprecated and ignored. Now, this target must be set in server
part.

max_connections = nolimit | Integer
Set this value to control the maximum number of connections from
HTTP clients into the server. This is implemented by closing the
last socket if the limit threshold is reached.

keepalive_maxuses = nolimit | Integer
Normally, Yaws does not restrict the number of times a connec‐
tion is kept alive using keepalive. Setting this parameter to an
integer X will ensure that connections are closed once they have
been used X times. This can be a useful to guard against long
running connections collecting too much garbage in the Erlang
VM.

process_options = undefined | Proplist
Set process spawn options for client acceptor processes. Op‐
tions must be specified as a quoted string of either the atom
undefined or as a proplist of valid process options. The sup‐
ported options are fullsweep_after, min_heap_size, and
min_bin_vheap_size, each taking an associated integer value.
Other process options are ignored. The proplist may also be
empty. See erlang:spawn_opt/4 for details on these options.

large_file_chunk_size = Integer
Set the chunk size used by Yaws to send large files. The default
value is 10240.

large_file_sendfile = erlang | disable
Set the version of sendfile method to use to send large files:

erlang - use file:sendfile/5.

disable - use gen_tcp:send/2.

The default value is erlang.

acceptor_pool_size = Integer
Set the size of the pool of cached acceptor processes. The spec‐
ified value must be greater than or equal to 0. The default
value is 8. Specifying a value of 0 effectively disables the
process pool.

log_wrap_size = Integer
The logs written by Yaws are all wrap logs, the default value at
the size where they wrap around and the original gets renamed to
File.old is 1000000, 1 megabyte. This value can be changed.
If we set the value to 0 the logs will never wrap. If we want to
use Yaws in combination with a more traditional log wrapper such
as logrotate, set the size to 0 and Yaws will reopen the log‐
files once they have be renamed/removed.

log_resolve_hostname = true | false
By default the client host IP is not resolved in the access
logs.

fail_on_bind_err = true | false
Fail completely or not if Yaws fails to bind a listen socket De‐
fault is true.

enable_soap = true | false
If true, a soap server will be started at startup of Yaws. De‐
fault is false.

soap_srv_mods = ListOfModuleSetting
If enable_soap is true, a startup Yaws will invoke
yaws_soap_srv:setup() to setup modules set here. ModuleSetting
is either a triad like <Mod, HandlerFunc, WsdlFile> or a quadru‐
ple form like <Mod, HandlerFunc, WsdlFile, Prefix> which speci‐
fies the prefix. A prefix will be used as argument of
yaws_soap_lib:initModel() and then be used as a XML namespace
prefix. Note, the WsdlFile here should be an absolute-path file
in local file systems.

For example, we can specify

soap_srv_mods=<Mod1, Handler, Wsdl1> <Mod2, Handler, Wsdl2, Prefix> ...

php_exe_path = Path
this target is deprecated and useless. use 'php_handler' target
in server part instead.
The name of (and possibly path to) the php executable used to
interpret php scripts (if allowed). Default is php_exe_path =
php-cgi.

copy_error_log = true | false
Enable or disable copying of the error log. When we run in em‐
bedded mode, there may very well be some other systems process
that is responsible for writing the errorlog to a file whereas
when we run in normal standalone mode, we typically want the Er‐
lang errorlog written to a report.log file. Default value is
true.

ysession_mod = Module
Allows specifying a different Yaws session storage mechanism in‐
stead of an ETS table. One of the drawbacks of the default
yaws_session_server implementation is that server side cookies
are lost when the server restarts. Specifying a different module
here will pass all write/read operations to this module (it must
implement appropriate callbacks).

ysession_cookiegen = Module
Allows specifying a different Yaws session cookie generator than
the built-in default. Module is expected to provide a
new_cookie/0 function that returns a session cookie in the form
of a list. Such a cookie generator module must be careful to re‐
turn a unique cookie each time it's called.

ysession_idle_timeout = Integer
Controls Yaws session idle cleanup. If a server has been idle
for ysession_idle_timeout milliseconds, check all Yaws sessions
and remove any that have timed out. The default yses‐
sion_idle_timeout value is 2*60*1000 (2 minutes).

ysession_long_timeout = Integer
Controls Yaws session periodic cleanup. Every yses‐
sion_long_timeout milliseconds, check all Yaws sessions and re‐
move any that have timed out. The default ysession_long_timeout
value is 60*60*1000 (1 hour).

runmod = ModuleName
At startup Yaws will invoke ModuleName:start() in a separate
process. It is possible to have several runmods. This is useful
if we want to reuse the Yaws startup shell script for our own
application.

pick_first_virthost_on_nomatch = true | false
When Yaws gets a request, it extracts the Host header from the
client request to choose a virtual server amongst all servers
with the same IP/Port pair. This configuration parameter de‐
cides whether Yaws should pick the first server (as defined in
the yaws.conf file) if no name match or not. If this is false
and no Host header is present in the request, Yaws returns a 400
Bad Request as required by the HTTP standard. In real live host‐
ing scenarios we typically want this to be false, whereas in
testing/development scenarios it may be convenient to set it to
true. Default is true.

keepalive_timeout = TimeInMilliseconds | infinity
If the HTTP session will be kept alive (i.e., not immediately
closed) it will close after keepalive_timeout milliseconds un‐
less a new request is received in that time. The default value
is 30000. The value infinity is legal but not recommended.

subconfig = File
Load specified config file. Absolute paths or relative ones to
the configuration location are allowed. Unix-style wildcard
strings can be used to include several files at once. See
filelib:wildcard/1 for details. Hidden files, starting by a dot,
will be ignored. For example:

subconfig = /etc/yaws/global.conf
subconfig = /etc/yaws/vhosts/*.conf

Or, relatively to the configuration location:

subconfig = global.conf
subconfig = vhosts/*.conf

subconfigdir = Directory
Load all config files found in the specified directory. The
given Directory can be an absolute path or relative to the con‐
figuration location. Hidden files, starting by a dot, will be
ignored.

x_forwarded_for_log_proxy_whitelist = ListOfUpstreamProxyServerIps
this target is deprecated and will be ignored.

default_type = MimeType
Defines the default MIME type to be used where Yaws cannot de‐
termine it by its MIME types mappings. Default is text/plain.

default_charset = Charset
Defines the default charset to be added when a response content-
type is text/*. By default, no charset is added.

mime_types_file = File
Overrides the default mime.types file included with Yaws. This
file must use the following format:

# Lines beginning with a '#' or a whitespace are ignored
# blank lines are also ignored
<MIME type> <space separated file extensions>

The default file is located at ${PRE‐
FIX}/lib/yaws/priv/mime.types. You should not edit this file be‐
cause it may be replaced when you upgrade your server.

add_types = ListOfTypes
Specifies one or more mappings between MIME types and file ex‐
tensions. More than one extension can be assigned to a MIME
type. ListOfTypes is defined as follows:

add_types = <MimeType1, Ext> <MimeType2, Ext1 Ext2 ...> ...

The mappings defined using this directive will overload all
other definitions. If a file extension is defined several times,
only the last one is kept. Multiple add_types directives may be
used.

add_charsets = ListOfCharsets
Specifies one or more mappings between charsets and file exten‐
sions. More than one extension can be assigned to a charset.
ListOfCharsets is defined as follows:

add_charsets = <Charset1, Ext> <Charset2, Ext1 Ext2 ...> ...

The mappings defined using this directive will overload all
other definitions. If a file extension is defined several times,
only the last one is kept. Multiple add_charsets directives may
be used.

sni = disable | enable | strict
Enables or disables the TLS SNI (Server Name Indication) sup‐
port.

When disabled (or not supported), all virtual servers in the
same group (same IP/Port) must share the same SSL configuration,
especially the same SSL certificate. Only the HTTP Host header
will be considered to find the right virtual server.

When enabled, SSL configuration can be different from a virtual
server to another, each one can have its own SSL certificate. In
this case, if a client provides a SNI hostname, it will be used
to find the right virtual server. To accept the SNI information
from the client, The first virtual server (the default one, see
pick_first_virthost_on_nomatch) must include TLS as a permitted
protocol.

If sni directive is set to enable, non SNI clients are allowed.
For such clients, virtual servers are selected as if Yaws did
not have SNI support. If it is set to strict, SNI hostname is
mandatary to access a SSL virtual server. But, in all cases,
when SNI support is enabled, if a client provides a SNI host‐
name, it must match the HTTP Host header (which is mandatory
too). Note that the first virtual server (the default one) will
be used for any request where the provided SNI hostname doesn't
match any of virtual server names. So, it is important that the
first virtual server have the most restrictive access control,
otherwise clients can access restricted resources by sending a
request for any unknown hostname. (This isn't actually any dif‐
ferent from using virtual servers without SNI support.)

The sni directive is a global one, so if you set it to strict,
non SNI clients will be refused for all SSL groups. See re‐
quire_sni directive from the server part to mitigate this re‐
quirement.

Default is disable.

WARNING: The SNI support was introduced in the SSL application
in Erlang/OTP 18.0, so Yaws ignores it for previous releases.

SERVER PART
Yaws can virthost several web servers on the same IP address as well as
several web servers on different IP addresses. This includes SSL
servers.

Each virtual host is defined within a matching pair of <server Server‐
Name> and </server>. The ServerName will be the name of the webserver.

The following directives are allowed inside a server definition.

port = Port
This makes the server listen on Port. Default is 8000.

listen = IpAddress
This makes the server listen on IpAddress. When virthosting
several servers on the same ip/port address, if the browser
doesn't send a Host: field, Yaws will pick the first server
specified in the config file. If the specified IP address is
0.0.0.0 Yaws will listen on all local IP addresses on the speci‐
fied port. Default is 127.0.0.1. Multiple listen directives may
be used to specify several addresses to listen on.

listen_backlog = Integer
This sets the TCP listen backlog for the server to define the
maximum length the queue of pending connections may grow to. The
default is 1024.

<listen_opts> ... </listen_opts>
Defines extra options to be set on the listen socket and, by in‐
heritance, on accepted sockets. See inet:setopts/2 for details.
Supported options are:

buffer = Integer (default: same as inet:setopts/2)

delay_send = true | false (default: same as inet:setopts/2)

linger = Integer | false (default: same as inet:setopts/2)

nodelay = true | false (default: same as inet:setopts/2)

priority = Integer (default: same as inet:setopts/2)

sndbuf = Integer (default: same as inet:setopts/2)

recbuf = Integer (default: same as inet:setopts/2)

send_timeout = Integer | infinity (default: same as inet:se‐
topts/2)

send_timeout_close = true | false (default: same as inet:se‐
topts/2)

server_signature = String
This directive sets the "Server: " output header to the custom
value and overloads the global one for this virtual server.

subconfig = File
Same as subconfig directive of the global part, but here files
should only contain directives allowed in the server part.

subconfigdir = Directory
Same as subconfigdir directive of the global part, but here
files should only contain directives allowed in server part.

rhost = Host[:Port]
This forces all local redirects issued by the server to go to
Host. This is useful when Yaws listens to a port which is dif‐
ferent from the port that the user connects to. For example,
running Yaws as a non-privileged user makes it impossible to
listen to port 80, since that port can only be opened by a priv‐
ileged user. Instead Yaws listens to a high port number port,
8000, and iptables are used to redirect traffic to port 80 to
port 8000 (most NAT:ing firewalls will also do this for you).

rmethod = http | https
This forces all local redirects issued by the server to use this
method. This is useful when an SSL off-loader, or stunnel, is
used in front of Yaws.

auth_log = true | false
Enable or disable the auth log for this virtual server. Default
is true.

access_log = true | false
Setting this directive to false turns off traffic logging for
this virtual server. The default value is true.

logger_mod = Module
It is possible to set a special module that handles access and
auth logging. The default is to log all web server traffic to
<Host>.access and <Host>.auth files in the configured or default
logdir.
This module must implement the behaviour yaws_logger. Default
value is yaws_log.

The following functions should be exported:

Module:open_log(ServerName, Type, LogDir)
When Yaws is started, this function is called for this vir‐
tual server. If the initialization is successful, the func‐
tion must return {true,State} and if an error occurred, it
must return false.

Module:close_log(ServerName, Type, State)
This function is called for this virtual server when Yaws
is stopped.

Module:wrap_log(ServerName, Type, State, LogWrapSize)
This function is used to rotate log files. It is regularly
called by Yaws and must return the possibly updated inter‐
nal NewState.

Module:write_log(ServerName, Type, State, Infos)
When it needs to log a message, Yaws will call this func‐
tion. The parameter Infos is {Ip,Req,InHdrs,OutHdrs,Time}
for an access log and {Ip,Path,Item} for an auth log,
where:

Ip - IP address of the accessing client (as a tuple).

Req - the HTTP method, URI path, and HTTP version of the
request (as a #http_request{} record).

InHdrs - the HTTP headers which were received from the WWW
client (as a #headers{} record).

OutHdrs - the HTTP headers sent to the WWW client (as a
#outh{} record)

Path - the URI path of the request (as a string).

Item - the result of an authentication request. May be
{ok,User}, 403 or {401,Realm}.

Time - The time taken to serve the request, in microsec‐
onds.

For all of these callbacks, ServerName is the virtual server's
name, Type is the atom access or auth and State is the internal
state of the logger.

shaper = Module
Defines a module to control access to this virtual server. Ac‐
cess can be controlled based on the IP address of the client. It
is also possible to throttle HTTP requests based on the client's
download rate. This module must implement the behaviour
yaws_shaper.

There is no such module configured by default.

dir_listings = true | true_nozip | false
Setting this directive to false disallows the automatic dir
listing feature of Yaws. A status code 403 Forbidden will be
sent. Set to true_nozip to avoid the auto-generated all.zip en‐
tries. Default is false.

extra_cgi_vars = .....
Add additional CGI or FastCGI variables. For example:

<extra_cgi_vars dir='/path/to/some/scripts'>
var = val
...
</extra_cgi_vars>

statistics = true | false
Turns on/off statistics gathering for a virtual server. Default
is false.

fcgi_app_server = Host:Port
The hostname and TCP port number of a FastCGI application
server. To specify an IPv6 address, put it inside square brack‐
ets (ex: "[::1]:9000"). The TCP port number is not optional.
There is no default value.

fcgi_trace_protocol = true | false
Enable or disable tracing of FastCGI protocol messages as info
log messages. Disabled by default.

fcgi_log_app_error = true | false
Enable or disable logging of application error messages (output
to stderr and non-zero exit value). Disabled by default.

deflate = true | false
Turns on or off deflate compression for a server. Default is
false.

<deflate> ... </deflate>
This begins and ends the deflate compression configuration for
this server. The following items are allowed within a matching
pair of <deflate> and </deflate> delimiters.

min_compress_size = nolimit | Integer
Defines the smallest response size that will be compressed.
If nolimit is not used, the specified value must be
strictly positive. The default value is nolimit.

compression_level = none | default | best_compression |
best_speed | 0..9
Defines the compression level to be used. 0 (none), gives
no compression at all, 1 (best_speed) gives best speed and
9 (best_compression) gives best compression. The default
value is default.

window_size = 9..15
Specifies the zlib compression window size. It should be in
the range 9 through 15. Larger values of this parameter re‐
sult in better compression at the expense of memory usage.
The default value is 15.

mem_level = 1..9
Specifies how much memory should be allocated for the in‐
ternal compression state. mem_level=1 uses minimum memory
but is slow and reduces compression ratio; mem_level=9 uses
maximum memory for optimal speed. The default value is 8.

strategy = default | filtered | huffman_only
This parameter is used to tune the compression algorithm.
See zlib(3erl) for more details on the strategy parameter.
The default value is default.

use_gzip_static = true | false
If true, Yaws will try to serve precompressed versions of
static files. It will look for precompressed files in the
same location as original files that end in ".gz". Only
files that do not fit in the cache are concerned. The de‐
fault value is false.

mime_types = ListOfTypes | defaults | all
Restricts the deflate compression to particular MIME types.
The special value all enable it for all types (It is a syn‐
onym of `*/*'). MIME types into ListOfTypes must have the
form `type/subtype' or `type/*' (indicating all subtypes of
that type). Here is an example:

mime_types = default image/*
mime_types = application/xml application/xhtml+xml application/rss+xml

By default, the following MIME types are compressed (if de‐
flate is set to true): text/*, application/rtf, applica‐
tion/msword, application/pdf, application/x-dvi, applica‐
tion/javascript. Multiple mime_types directives can be
used.

docroot = Directory ...
This makes the server serve all its content from Directory.
It is possible to pass a space-separated list of directories as
docroot. If this is the case, the various directories will be
searched in order for the requested file. This also works with
the ssi and yssi constructs where the full list of directories
will be searched for files to ssi/yssi include. Multiple docroot
directives can be used. You need at least one valid docroot,
invalid docroots are skipped with their associated auth struc‐
tures.

auth_skip_docroot = true | false
If true, the docroot will not be searched for .yaws_auth files.
This is useful when the docroot is quite large and the time to
search it is prohibitive when Yaws starts up. Defaults to false.

partial_post_size = Integer | nolimit
When a Yaws file receives large POSTs, the amount of data re‐
ceived in each chunk is determined by this parameter. The de‐
fault value is 10240. Setting it to nolimit is potentially dan‐
gerous.

dav = true | false
Turns on the DAV protocol for this server. The dav support in
Yaws is highly limited. If dav is turned on, .yaws processing of
.yaws pages is turned off. Default is false. The socket read
timeout is supplied by the keepalive_timeout setting. If the
read is not done within the timeout, the POST will fail.

tilde_expand = true|false
If this value is set to false Yaws will never do tilde expan‐
sion. The default is false. tilde_expansion is the mechanism
whereby a URL on the form http://www.foo.com/~username is
changed into a request where the docroot for that particular re‐
quest is set to the directory ~username/public_html/.

allowed_scripts = ListOfSuffixes
The allowed script types for this server. Recognized are
`yaws', `cgi', `fcgi', `php'. Default is allowed_scripts = yaws
php cgi fcgi.

Note: for fcgi scripts, the FastCGI application server is only
called if a local file with the .fcgi extension exists. However,
the contents of the local .fcgi file are ignored.

tilde_allowed_scripts = ListOfSuffixes
The allowed script types for this server when executing files in
a users public_html folder Recognized are `yaws', `cgi', `fcgi',
`php'. Default is tilde_allowed_scripts = i.e. empty

index_files = ListOfResources
This directive sets the list of resources to look for, when a
directory is requested by the client. If the last entry begins
with a `/', and none of the earlier resources are found, Yaws
will perform a redirect to this uri. Default is index_files =
index.yaws index.html index.php.

appmods = ListOfModuleNames
If any of the names in ListOfModuleNames appear as components in
the path for a request, the path request parsing will terminate
and that module will be called. There is also an alternate syn‐
tax for specifying the appmods if we don't want our internal er‐
lang module names to be exposed in the URL paths. We can spec‐
ify

appmods = <Path1, Module1> <Path2, Modules2> ...

Assume for example that we have the URL http://www.hy‐
ber.org/myapp/foo/bar/baz?user=joe while we have the module foo
defined as an appmod, the function foo:out(Arg) will be invoked
instead of searching the filesystems below the point foo.
The Arg argument will have the missing path part supplied in its
appmoddata field.

It is also possible to exclude certain directories from appmod
processing. This is particulaly interesting for '/' appmods.
Here is an example:

appmods = </, myapp exclude_paths icons js top/static>

The above configuration will invoke the 'myapp' erlang module on
everything except any file found in directories 'icons', 'js'
and 'top/static' relative to the docroot.

dispatchmod = DispatchModule
Set DispatchModule as a server-specific request dispatching mod‐
ule. Yaws expects DispatchModule to export a dispatch/1 func‐
tion. When it receives a request, Yaws passes an #arg{} record
to the dispatch module's dispatch/1 function, which returns one
of the following atom results:

done - this indicates the dispatch module handled the re‐
quest itself and already sent the response, and Yaws should
resume watching for new requests on the connection

closed - same as done but the DispatchModule also closed
the connection

continue - the dispatch module has decided not to handle
the request, and instead wants Yaws to perform its regular
request dispatching

Note that when DispatchModule handles a request itself, Yaws
does not support tracing, increment statistics counters or allow
traffic shaping for that request. It does however still keep
track of maximum keepalive uses on the connection.

errormod_404 = Module
It is possible to set a special module that handles 404 Not
Found messages. The function Module:out404(Arg, GC, SC) will be
invoked. The arguments are

Arg - a #arg{} record

GC - a #gconf{} record (defined in yaws.hrl)

SC - a #sconf{} record (defined in yaws.hrl)

The function can and must do the same things that a normal out/1
does.

errormod_401 = Module
It is possible to set a special module that handles 401 Unautho‐
rized messages. This can for example be used to display a login
page instead. The function Module:out401(Arg, Auth, Realm) will
be invoked. The arguments are

Arg - a #arg{} record

Auth - a #auth{} record

Realm - a string

The function can and must do the same things that a normal out/1
does.

errormod_crash = Module
It is possible to set a special module that handles the HTML
generation of server crash messages. The default is to display
the entire formatted crash message in the browser. This is good
for debugging but not in production.
The function Module:crashmsg(Arg, SC, Str) will be called. The
Str is the real crash message formatted as a string.
The function must return, {content,MimeType,Cont} or {html, Str}
or {ehtml, Term}. That data will be shipped to the client.

expires = ListOfExpires
Controls the setting of the Expires HTTP header and the max-age
directive of the Cache-Control HTTP header in server responses
for specific MIME types. The expiration date can be set as rela‐
tive to either the time the source file was last modified; as
the time of the client access; or as always in order to empty
the cache altogether. ListOfExpires is defined as follows:

expires = <MimeType1, access+Seconds> <MimeType2, modify+Seconds> <MimeType3, always> ...

A MimeType can also have a wildcard as subtype or both as sub‐
type and type, like type/* or */*.

These HTTP headers are an instruction to the client about the
document's validity and persistence. If cached, the document may
be fetched from the cache rather than from the source until this
time has passed. After that, the cache copy is considered "ex‐
pired" and invalid, and a new copy must be obtained from the
source. Here is an example:

expires = <image/gif, access+2592000> <image/png, access+2592000>
expires = <image/jpeg, access+2592000> <text/css, access+2592000>
expires = <text/*, always>

and here is another:

expires = <*/*, always>

arg_rewrite_mod = Module
It is possible to install a module that rewrites all the Arg
#arg{} records at an early stage in the Yaws server. This can
be used to do various things such as checking a cookie, rewrit‐
ing paths etc. An arg_rewrite_mod must export an arg_rewrite/1
function taking and returning an #arg{} record. If the function
wants to return a response, it must set the #arg.state field of
its return value to an instance of the #rewrite_response{}
record.

The module yaws_vdir can be used in case you want to serve
static content that is not located in your docroot. See the ex‐
ample at the bottom of this man page for how to use the opaque +
vdir elements to instruct the yaws_vdir module what paths to re‐
write.

start_mod = Module
Defines a user provided callback module. At startup of the
server, Module:start/1 will be called. The #sconf{} record (de‐
fined in yaws.hrl) will be used as the input argument. This
makes it possible for a user application to synchronize the
startup with the Yaws server as well as getting hold of user
specific configuration data, see the explanation for the
<opaque> context.

revproxy = Prefix Url [intercept_mod Module]
Make Yaws a reverse proxy. Prefix is a path inside our own doc‐
root and Url argument is a URL pointing to a website we want to
"mount" under the Prefix path. This example:

revproxy = /tmp/foo http://yaws.hyber.org

makes the hyber website appear under /tmp/foo.

It is possible to have multiple reverse proxies inside the same
server.

You can optionally configure an interception module for each re‐
verse proxy, allowing your application to examine and modify re‐
quests and HTTP headers as they pass through the proxy from
client to backend server and also examine and modify responses
and HTTP headers as they return from the backend server through
the proxy to the client.

You specify an interception module by including the optional in‐
tercept_mod keyword followed by Module, which should be the name
of your interception module.

An interception module is expected to export two functions: re‐
write_request/2 and rewrite_response/2. The two arguments passed
to rewrite_request/2 function are a #http_request{} record and a
#headers{} record, whereas rewrite_response/2 function takes a
#http_response{} record and also a #headers{} record. You can
find definitions for these record types in the yaws_api.hrl
header file. Each function can examine each record instance and
can either return each original instance or can return a modi‐
fied copy of each instance in its response. The rewrite_re‐
quest/2 function should return a tuple of the following form:

{ok, #http_request{}, #headers{}}

and the rewrite_response/2 function should similarly return a
tuple of the following form:

{ok, #http_response{}, #headers{}}

A #headers{} record can easily be manipulated in an interceptor
using the functions listed below:

yaws_api:set_header/2, yaws_api:set_header/3
yaws_api:get_header/2, yaws_api:get_header/3
yaws_api:delete_header/2

Any failures in your interception module's functions will result
in HTTP status code 500, indicating an internal server error.

fwdproxy = true|false
Make Yaws a forward proxy. By enabling this option you can use
Yaws as a proxy for outgoing web traffic, typically by configur‐
ing the proxy settings in a web-browser to explicitly target
Yaws as its proxy server.

servername = Name
If we're virthosting several servers and want to force a server
to match specific Host: headers we can do this with the "server‐
name" directive. This name doesn't necessarily have to be the
same as the the name inside <server Name> in certain NAT scenar‐
ios. Rarely used feature.

serveralias = ListOfNames

This directive sets the alternate names for a virtual host. A
server alias may contain wildcards:
'*' matches any sequence of zero or more characters
'?' matches one character unless that character is a pe‐
riod ('.')

Multiple serveralias directives may be used. Here is an example:

<server server.domain.com>
serveralias = server server2.domain.com server2
serveralias = *.server.domain.com *.server?.domain.com
...
</server>

php_handler = <Type, Spec>
Set handler to interpret .php files. It can be one of the fol‐
lowing definitions:

php_handler = <cgi, Filename> - The name of (and possibly path
to) the php executable used to interpret php scripts (if al‐
lowed).

php_handler = <fcgi, Host:Port> - Use the specified fastcgi
server to interpret .php files (if allowed).

Yaws does not start the PHP interpreter in fastcgi mode for
you. To run PHP in fastcgi mode, call it with the -b op‐
tion. For example:

php5-cgi -b '127.0.0.1:54321'

This starts a php5 in fastcgi mode listening on the local
network interface. To make use of this PHP server from
Yaws, specify:

php_handler = <fcgi, 127.0.0.1:54321>

If you need to specify an IPv6 address, use square brack‐
ets:

php_handler = <fcgi, [::1]:54321>

The PHP interpreter needs read access to the files it is to
serve. Thus, if you run it in a different security context
than Yaws itself, make sure it has access to the .php
files.
Please note that anyone who is able to connect to the php
fastcgi server directly can use it to read any file to
which it has read access. You should consider this when
setting up a system with several mutually untrusted in‐
stances of php.

php_handler = <extern, Module:Function | Node:Module:Function> -
Use an external handler, possibly on another node, to interpret
.php files (if allowed).

To interpret a .php file, the function Module:Function(Arg)
will be invoked (Evaluated inside a rpc call if a Node is
specified), where Arg is an #arg{} record.
The function must do the same things that a normal out/1
does.

Default value is <cgi, "/usr/bin/php-cgi">.

phpfcgi = Host:Port
this target is deprecated. use 'php_handler' target in server
part instead.
Using this directive is the same as: php_handler = <fcgi,
Host:Port>.

default_type = MimeType
Overloads the global default_type value for this virtual server.

default_charset = Charset
Overloads the global default_charset value for this virtual
server.

mime_types_file = File
Overloads the global mime_type_file value for this virtual
server. Mappings defined in File will not overload those defined
by add_types directives in the global part.

add_types = ListOfTypes
Overloads the global add_types values for this virtual server.
If a mapping is defined in the global part and redefined in a
server part using this directive, then it is replaced. Else it
is kept.

add_charsets = ListOfCharsets
Overloads the global add_charsets values for this virtual
server. If a mapping is defined in the global part and redefined
in a server part using this directive, then it is replaced. Else
it is kept.

nslookup_pref = [inet | inet6]
For fcgi servers and revproxy URLs, define the name resolution
preference. For example, to perform only IPv4 name resolution,
use [inet]. To do both IPv4 and IPv6 but try IPv6 first, use
[inet6, inet]. Default value is [inet].

This begins and ends an SSL configuration for this server. It's
possible to virthost several SSL servers on the same IP/Port. If
SNI support is disabled or not supported, they must share the
same certificate configuration. In this situation, it is compli‐
cated to virthost several SSL servers on the same IP/Port since
the certificate is typically bound to a domainname in the common
name part of the certificate. One solution to this problem is to
have a certificate with multiple subjectAltNames. If SNI support
is enabled, SSL servers on the same IP/Port can have their own
SSL configuration with a different SSL certificate for each one.
See the global sni directive.

The SNI support was introduced in the SSL application in Er‐
lang/OTP 18.0. It is an extension to the TLS protocol (RFC
4366), which allows the client to include the requested hostname
in the first message of its SSL handshake.

See also http://wiki.cacert.org/VhostTaskForce#Interoperabil‐
ity_Test for browser compatibility.

keyfile = File
Specifies which file contains the private key for the cer‐
tificate. If not specified then the certificate file will
be used.

certfile = File
Specifies which file contains the certificate for the
server.

cacertfile = File
A file containing trusted certificates to use during client
authentication and to use when attempting to build the
server certificate chain. The list is also used in the
list of acceptable client CAs passed to the client when a
certificate is requested.

dhfile = File
A file containing PEM-encoded Diffie-Hellman parameters to
be used by the server if a cipher suite using Diffie-Hell‐
man key exchange is negotiated. If not specified, default
parameters are used.

verify = verify_none | verify_peer
Specifies the level of verification the server does on
client certs. Setting verify_none means that the x509 vali‐
dation will be skipped (no certificate request is sent to
the client), verify_peer means that a certificate request
is sent to the client (x509 validation is performed.

You might want to use fail_if_no_peer_cert in combination
with verify_peer.

fail_if_no_peer_cert = true | false
If verify is set to verify_peer and set to true the connec‐
tion will fail if the client does not send a certificate
(i.e. an empty certificate). If set to false the server
will fail only if an invalid certificate is supplied (an
empty certificate is considered valid).

depth = Int
Specifies the depth of certificate chains the server is
prepared to follow when verifying client certs. For the OTP
new SSL implementation it is also used to specify how far
the server, i.e. we, shall follow the SSL certificates we
present to the clients. Hence, using self-signed certs, we
typically need to set this to 0.

password = String
If the private key is encrypted on disc, this password is
the 3DES key to decrypt it.

ciphers = String
This string specifies the SSL cipher string. The syntax of
the SSL cipher string is an erlang term compliant with the
output of ssl:cipher_suites().

ciphers = "[{dhe_rsa,aes_256_cbc,sha}, \
{dhe_dss,aes_256_cbc,sha}]"

eccs = String
This string specifies the supported Elliptic Curve Cryptog‐
raphy (ECC). It must be a subset of ssl:eccs(). For PCI
DSS compliance (which is the main reason why you would want
to change this), set it on a single line to:

eccs = "[sect571r1, sect571k1, secp521r1, brainpoolP512r1, \
sect409k1, sect409r1, brainpoolP384r1, secp384r1, \
sect283k1, sect283r1, brainpoolP256r1, secp256k1, \
secp256r1, sect239k1, xsect233k1, sect233r1, \
secp224k1, secp224r1]"

secure_renegotiate = true | false
Specifies whether to reject renegotiation attempt that does
not live up to RFC 5746. By default secure_renegotiate is
set to false i.e. secure renegotiation will be used if pos‐
sible but it will fallback to unsecure renegotiation if the
peer does not support RFC 5746.

client_renegotiation = true | false
Enables or disables the Erlang/OTP SSL application client
renegotiation option. Defaults to true. See the ssl manual
page at http://www.erlang.org/doc/man/ssl.html for more de‐
tails.

WARNING: This option was introduced in the SSL application
in Erlang/OTP 18.0, so Yaws ignores it for previous re‐
leases.

honor_cipher_order = true | false
If true (the default), use the server's preference for ci‐
pher selection. If false, use the client's preference.

WARNING: This option was introduced in the SSL application
in Erlang/OTP 17.0, so Yaws ignores it for previous re‐
leases.

protocol_version = ProtocolList
Specifies the list of SSL protocols that will be supported.
If not set, defaults to all protocols supported by the er‐
lang ssl application. For example, to support only TLS ver‐
sions 1.2, 1.1, and 1:

protocol_version = tlsv1.2, tlsv1.1, tlsv1

require_sni = true | false
If true,the server will reject non SNI clients and clients
providing an unknown SNI hostname (this last remark is only
relevant for the first virtual server of a SSL group). This
directive is ignored if SNI support is disabled (or not
supported).

Default is false.

<redirect> ... </redirect>
Defines a redirect mapping. The following items are allowed
within a matching pair of <redirect> and </redirect> delimiters.

We can have a series of redirect rules in one of the formats be‐
low:

Path = URL
Path = code
Path = code URL

Path must be an url-decoded path beginning with a slash. URL may
be either a relative URL (a path beginning with a slash), or an
absolute URL. In the first case, the scheme:hostname:port of the
current server will be added. All accesses to Path will be redi‐
rected to URL/Path (or scheme:hostname:port/URL/Path if URL is
relative). URL must be url-encoded. Note that the original path
is appended to the redirected URL.

For example, assume we have the following redirect configura‐
tion:

<redirect>
/foo = http://www.mysite.org/zapp
/bar = /tomato.html
</redirect>

Assuming this config resides on a site called http://abc.com, we
have the following redirects:

http://abc.com/foo -> http://www.mysite.org/zapp/foo
http://abc.com/foo/test -> http://www.mysite.org/zapp/foo/test
http://abc.com/bar -> http://abc.com/tomato.html/bar
http://abc.com/bar/x/y/z -> http://abc.com/tomato.html/bar/x/y/z

By default, Yaws will perform a 302 redirect. The HTTP status
code can be changed using the code parameter. Note that the sta‐
tus code must be known by Yaws.

• For 3xx status codes, the URL parameter must be present and
will be used to build the new location.

• For other status codes (1xx, 2xx, 4xx and 5xx), it can be
omitted. In the absence of URL, Yaws will return a generic
response with the specified status code.

• Otherwise, the URL parameter must be a relative URL and will
be used to customize the response.

Sometimes we do not want to have the original path appended to
the redirected path. To get that behaviour we specify the config
with '==' instead of '='.

<redirect>
/foo == http://www.mysite.org/zapp
/bar = /tomato.html
</redirect>

Now a request for http://abc.com/foo/x/y/z simply gets redi‐
rected to http://www.mysite.org/zapp. This is typically used
when we simply want a static redirect at some place in the doc‐
root.

When we specify a relative URL as the target for the redirect,
the redirect will be to the current http(s) server.

<auth> ... </auth>
Defines an auth structure. The following items are allowed
within a matching pair of <auth> and </auth> delimiters.

docroot = Docroot
If a docroot is defined, this auth structure will be tested
only for requests in the specified docroot. No docroot con‐
figured means all docroots. If two auth structures are de‐
fined, one with a docroot and one with no docroot, the
first of both overrides the second one for requests in the
configured docroot.

dir = Dir
Makes Dir to be controlled by WWW-authenticate headers. In
order for a user to have access to WWW-Authenticate con‐
trolled directory, the user must supply a password. The Dir
must be specified relative to the docroot. Multiple dir
can be used. If no dir is set, the default value, "/", will
be used.

realm = Realm
In the directory defined here, the WWW-Authenticate Realm
is set to this value.

authmod = AuthMod
If an auth module is defined then AuthMod:auth(Arg, Auth)
will be called for all access to the directory. The auth/2
function should return one of: true, false, {false, Realm},
{appmod, Mod}. If {appmod, Mod} is returned then a call to
Mod:out401(Arg, Auth, Realm) will be used to deliver the
content. If errormod_401 is defined, the call to Mod will
be ignored. (Mod:out(Arg) is deprecated).

This can, for example, be used to implement cookie authen‐
tication. The auth() callback would check if a valid
cookie header is present, if not it would return {appmod,
?MODULE} and the out401/1 function in the same module would
return {redirect_local, "/login.html"}.

user = User:Password | "User:{Algo}Hash" |
"User:{Algo}$Salt$Hash"
Inside this directory, the user User has access if the user
supplies the password Password in the popup dialogue pre‐
sented by the browser. It is also possible to provide a
hashed password, encoded in base64. In that case, the algo‐
rithm used to hash the password must be set. Algo must be a
one of the following algorithms:

md5 | ripemd160 | sha | sha224 | sha256 | sha384 | sha512

It is possible to use salted hashes. If so, the Salt must
be provided, encoded in base64. We can obviously have sev‐
eral of these value inside a single <auth> </auth> pair.

pam service = pam-service
If the item pam is part of the auth structure, Yaws will
also try to authenticate the user using "pam" using the pam
service indicated. Usual services are typically found under
/etc/pam.d. Usual values are "system-auth" etc.

pam authentication is performed by an Erlang port program
which is typically installed as suid root by the Yaws in‐
stall script.

allow = all | ListOfHost
The allow directive affects which hosts can access an area
of the server. Access can be controlled by IP address or IP
address range. If all is specified, then all hosts are al‐
lowed access, subject to the configuration of the deny and
order directives. To allow only particular hosts or groups
of hosts to access the server, the host can be specified in
any of the following formats:

A full IP address
allow = 10.1.2.3
allow = 192.168.1.104, 192.168.1.205

A network/netmask pair
allow = 10.1.0.0/255.255.0.0

A network/nnn CIDR specification
allow = 10.1.0.0/16

deny = all | ListOfHost
This directive allows access to the server to be restricted
based on IP address. The arguments for the deny directive
are identical to the arguments for the allow directive.

order = Ordering
The order directive, along with allow and deny directives,
controls a three-pass access control system. The first pass
processes either all allow or all deny directives, as spec‐
ified by the order directive. The second pass parses the
rest of the directives (deny or allow). The third pass ap‐
plies to all requests which do not match either of the
first two.

Ordering is one of (Default value is deny,allow):

allow,deny
First, all allow directives are evaluated; at least
one must match, or the request is rejected. Next,
deny directives are evaluated. If any matches, the
request is rejected. Last, any requests which do not
match an allow or a deny directive are denied by de‐
fault.

deny,allow
First, all deny directives are evaluated; if any
matched, the request is denied unless it also
matches an allow directive. Any requests which do
not match any allow or deny directives are permit‐
ted.

<opaque> ... </opaque>
This begins and ends an opaque configuration context for this
server, where 'Key = Value' directives can be specified. These
directives are ignored by Yaws (hence the name opaque), but can
be accessed as a list of tuples {Key,Value} stored in the
#sconf.opaque record entry. See also the description of the
start_mod directive.

This mechanism can be used to pass data from a surrounding ap‐
plication into the individual .yaws pages.

strip_undefined_bindings = true | false
Change the behavior of the {bindings, [...]} directive to treat
all undefined keys found in returned out/1 content as if they
were defined with an empty value, resulting in all undefined
bindings effectively being stripped out of returned content. By
default, strip_undefined_bindings is false, which means unde‐
fined bindings are ignored and their text is left as is in re‐
turned content.

This setting applies only for out/1 content, not to static pages
or other returned content.

<extra_response_headers> ... </extra_response_headers>
This begins and ends a configuration context for extra response
headers for this server, where directives for adding headers,
erasing headers, and modules for handling extra response headers
can be specified as follows:

add Hdr = Value
Add Hdr with value Value to the response, but only
if the response status code is one of these values:

200 OK
201 Created
204 No Content
206 Partial Content
301 Moved Permanently
302 Found
303 See Other
304 Not Modified
307 Temporary Redirect
308 Permanent Redirect

For any other status code, Hdr is not added.

always add Hdr = Value
Unconditionally add Hdr with value Value to the re‐
sponse, regardless of the response status code.

erase Hdr
Remove Hdr and its associated value from the re‐
sponse.

extramod = Module
Specifies a module to call to process extra response
headers. Yaws calls Module:extra_response_headers/3
passing the following arguments:

Response headers
An Erlang map holding the response head‐
ers with header name strings as keys and
strings as header values

Arg An #arg{} record representing the re‐
quest

{StatusCode,Version}
A tuple where StatusCode is the numeric
HTTP status code for the response, and
Version is a tuple specifying the HTTP
version, e.g. {1,1} for HTTP 1.1.

The Module:extra_response_headers/3 function should return
either the original header map or a modified map where
headers have been added, changed, or deleted. Added headers
are not subject to the status code restrictions for the add
extra response header directive, but the function can call
yaws_api:http_extra_response_headers_add_status_codes/0 to
retrieve the list of the status codes for which adding
headers is normally allowed.

For response headers that can have multiple settings, such
as Set-Cookie, multiple values can be specified in the ex‐
tra response header map by using a value of {multi,
[Value]} where [Value] is a list of one or more header val‐
ues. The Set-Cookie header is a standard special case for
which Yaws converts a multi header into a separate Set-
Cookie header for each value; for other headers, Yaws con‐
verts a multi header into a single HTTP header with a
comma-separated value.

Note that extra response headers do not apply to responses returned di‐
rectly by any DispatchModule.

EXAMPLES
The following example defines a single server on port 80.

logdir = /var/log/yaws
<server www.mydomain.org>
port = 80
listen = 192.168.128.31
docroot = /var/yaws/www
</server>

And this example shows a similar setup but two web servers on the same
IP address.

logdir = /var/log/yaws
<server www.mydomain.org>
port = 80
listen = 192.168.128.31
docroot = /var/yaws/www
</server>

<server www.funky.org>
port = 80
listen = 192.168.128.31
docroot = /var/yaws/www_funky_org
</server>

An example with www-authenticate and no access logging at all.

logdir = /var/log/yaws
<server www.mydomain.org>
port = 80
listen = 192.168.128.31
docroot = /var/yaws/www
access_log = false
<auth>
dir = secret/dir1
realm = foobar
user = jonny:verysecretpwd
user = benny:thequestion
user = ronny:havinganamethatendswithy
</auth>
</server>

An example specifying a user defined module to be called at startup, as
well as some user specific configuration.

<server www.funky.org>
port = 80
listen = 192.168.128.31
docroot = /var/yaws/www_funky_org
start_mod = btt
<opaque>
mydbdir = /tmp
mylogdir = /tmp/log
</opaque>
</server>

An example specifying the GSSAPI/SPNEGO module (authmod_gssapi) to be
used for authentication. This module requires egssapi version 0.1~pre2
or later available at http://www.hem.za.org/egssapi/.

The Kerberos5 keytab is specified as 'keytab = File' directive in
opaque. This keytab should contain the keys of the HTTP service princi‐
pal, 'HTTP/www.funky.org' in this example.

<server www.funky.org>
port = 80
listen = 192.168.128.31
docroot = /var/yaws/www_funky_org
start_mod = authmod_gssapi
<auth>
authmod = authmod_gssapi
dir = secret/dir1
</auth>
<opaque>
keytab = /etc/yaws/http.keytab
</opaque>
</server>

And finally a slightly more complex example with two servers on the
same IP, and one SSL server on a different IP.

When there are more than one server on the same IP, and they have dif‐
ferent names the server must be able to choose one of them if the
client doesn't send a Host: header. Yaws will choose the first one de‐
fined in the conf file.

logdir = /var/log/yaws
max_num_cached_files = 8000
max_num_cached_bytes = 6000000

<server www.mydomain.org>
port = 80
listen = 192.168.128.31
docroot = /var/yaws/www
</server>

<server www.funky.org>
port = 80
listen = 192.168.128.31
docroot = /var/yaws/www_funky_org
</server>

<server www.funky.org>
port = 443
listen = 192.168.128.32
docroot = /var/yaws/www_funky_org
<ssl>
keyfile = /etc/funky.key
certfile = /etc/funky.cert
password = gazonk
</ssl>
</server>

Finally an example with virtual directories, vdirs.

<server server.domain>
port = 80
listen = 192.168.128.31
docroot = /var/yaws/www
arg_rewrite_mod = yaws_vdir
<opaque>
vdir = "/virtual1/ /usr/local/somewhere/notrelated/to/main/docroot"
vdir = "/myapp/ /some/other/path can include/spaces"
vdir = "/icons/ /usr/local/www/yaws/icons"
</opaque>
</server>

The first defined vdir can then be accessed at or under
http://server.domain/virtual1/ or http://server.domain/virtual1

AUTHOR
Written by Claes Wikstrom

Yaws

Examples

Misc