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gstrauss, 2016-12-29 09:02

Server-Side Includes

Module: mod_ssi


SSI is a very old and cheap way to generate content dynamically on server-side.

The use of this module is strongly discouraged:
  • the execution of a SSI script is done in the server-core
  • a long-running SSI script blocks the handling of ALL connections
  • as soon as you use #exec the performance gets worse than using CGI scripts directly
You should only use SSI for two reason:
  • content assembling with #include
  • legacy applications


You have to load the mod_ssi module and set the ssi.extension:

server.modules = ( ..., "mod_ssi", ... ) #Note that if you use mod_compress mod_ssi must come first to function.



List of file extensions that should be interpreted via mod_ssi.


ssi.extension = ( ".shtml" )


Content type of the pages being served via mod_ssi.
Default value: text/html


Enable/disable conditional request handling and generate ETag and Last-Modified response headers.
This should not be enabled unless the SSI requests are known to generate cacheable documents. An SSI page which only includes contents from other static files and/or which uses SSI commands that produce predictable output may be cacheable.
Default value: disable


Enable/disable #exec cmd="..." execution
Default value: enable

ssi.recursion-max (since 1.4.44)

Default value: 0 (disabled)
Set the max recursion depth for #include virtual="..." SSI processing. The default, 0, preserves the existing behavior of simply including the file.

Available Elements

 <!--#echo var="..." -->
 <!--#echo var="DOCUMENT_ROOT"-->
 <!--#include file="..."\|virtual="..." -->
 <!--#flastmod file="..."\|virtual="..." -->
 <!--#fsize file="..."\|virtual="..." -->
 <!--#config timefmt="..." sizefmt="(bytes|abbrev)" -->
 <!--#printenv -->
 <!--#set var="..." value="..." -->
 <!--#if expr="..." -->
 <!--#elif expr="..." -->
 <!--#else -->
 <!--#endif -->
 <!--#exec cmd="..." -->
 <!--#exec cmd="date"-->

Expression Handling

Every "expr" is interpreted:
  • logical: AND, OR, !
  • compare: =, <, <=, >, =>, !=
  • precedence: (, )
  • quoted strings: 'string with a dollar: $FOO'
  • variable substitution: $REMOTE_ADDR
  • unquoted strings: string

Flow Control

if, elif, else and endif can only be used to insert content under special conditions.

Unsupported Features (Not Implemented)

The original SSI module from NCSA and Apache provided some more options which are not supported by this module for various reasons:

Quick and Dirty Notes from the 90s or How to enable (Server Side Instruction)

  • You need to activate the module `mod_ssi` berfor the module `mod_compress`!
  • You need to set the variable in lighttpd.conf `ssi.extension = (".html")`.
    (Here we say that every `.html` file can have `` or other SSI instructions. The filetype extension of the included file is not relevant!)
  • Cheers to the 90s

Updated by gstrauss over 6 years ago · 24 revisions