How to view a list of modules in Apache

Apache is a popular open-source web server that supports various functionalities through the use of modules. Modules can provide additional features such as URL rewriting, security mechanisms, caching, and more.

Managing Apache modules involves knowing which modules are installed, enabled, or available within your system. This is crucial for optimizing your server's performance and ensuring that you have the necessary components for running specific web applications.

Whether you're troubleshooting a problem or planning to install new modules, having a complete understanding of what's currently running on your Apache server is vital. In this guide, we'll cover the steps to list installed, available, or enabled Apache modules in different environments. Ubuntu for example uses apachectl and a2query while Red-Hat based distro uses httpd and does not have a2query.

1. List modules that are enabled or currently active.

   $ apache2ctl -M
   Loaded Modules:
   core_module (static)
   so_module (static)
   ...
   rewrite_module (shared)

   Module Type	Description
   Static	These are the modules that are compiled directly into the main httpd binary. They are always present and do not need to be loaded separately. The main advantage is performance, but the drawback is that adding or removing a static module requires recompiling Apache.
   Shared	Shared modules are compiled as separate shared objects. They can be loaded or unloaded at runtime using directives in Apache's configuration file without recompiling the entire Apache binary. This makes adding or removing functionality more flexible.
   Dynamic	These are similar to shared modules but are generally used to refer to modules that can be loaded or unloaded at runtime without a server restart. Typically, modern Apache installations use shared modules in place of truly dynamic ones.

   Related: Default Apache Configuration Files
   Related: How to Enable and Disable Apache Modules

2. Filter for specific module using grep.

   $ apache2ctl -M | grep rewrite
   rewrite_module (shared)

3. List modules that are available or modules that are present on your system but may or may not be enabled.

   $ ls /etc/apache2/mods-available
   access_compat.load auth_basic.load ...
   authz_user.load rewrite.load

   This directory contains all the available modules on a Debian-based system. The location may vary depending on the distribution.

4. List enabled modules using a2query.

   $ a2query -m
   rewrite (enabled by site administrator)
   reqtimeout (enabled by maintainer script)
   env (enabled by maintainer script)
   deflate (enabled by maintainer script)
   negotiation (enabled by maintainer script)
   proxy_http (enabled by site administrator)
   authn_core (enabled by maintainer script)
   dir (enabled by maintainer script)
   authz_core (enabled by maintainer script)
   setenvif (enabled by maintainer script)
   autoindex (enabled by maintainer script)
   auth_basic (enabled by maintainer script)
   authz_host (enabled by maintainer script)
   alias (enabled by maintainer script)
   authz_user (enabled by maintainer script)
   access_compat (enabled by maintainer script)
   proxy (enabled by site administrator)
   filter (enabled by maintainer script)
   mpm_event (enabled by maintainer script)
   mime (enabled by maintainer script)
   authn_file (enabled by maintainer script)

5. List specific module using a2query.

   $ a2query -m rewrite
   rewrite (enabled by site administrator)

6. List available and enabled modules in Ubuntu and similar systems.

   $ ls /etc/apache2/mods-*
   /etc/apache2/mods-available:
   access_compat.load    dir.conf                  proxy_express.load
   actions.conf          dir.load                  proxy_fcgi.load
   actions.load          dump_io.load              proxy_fdpass.load
   alias.conf            echo.load                 proxy_ftp.conf
   alias.load            env.load                  proxy_ftp.load
   allowmethods.load     expires.load              proxy_hcheck.load
   asis.load             ext_filter.load           proxy_html.conf
   ##### snipped
   
   /etc/apache2/mods-enabled:
   access_compat.load  authz_user.load  filter.load       proxy.conf
   alias.conf          autoindex.conf   heartbeat.load    proxy_http.load
   alias.load          autoindex.load   mime.conf         proxy.load
   auth_basic.load     deflate.conf     mime.load         reqtimeout.conf
   authn_core.load     deflate.load     mpm_event.conf    reqtimeout.load
   authn_file.load     dir.conf         mpm_event.load    setenvif.conf
   authz_core.load     dir.load         negotiation.conf  setenvif.load
   authz_host.load     env.load         negotiation.load

7. List available and enabled modules in CentOS and similar systems.

   $ ls /etc/httpd/*modules*/
   /etc/httpd/conf.modules.d/:
   00-base.conf    00-dav.conf  00-mpm.conf       00-proxy.conf    01-cgi.conf  10-proxy_h2.conf
   00-brotli.conf  00-lua.conf  00-optional.conf  00-systemd.conf  10-h2.conf   README
   
   /etc/httpd/modules/:
   mod_access_compat.so    mod_cgid.so                 mod_log_config.so      mod_reflector.so
   mod_actions.so          mod_cgi.so                  mod_log_debug.so       mod_remoteip.so
   mod_alias.so            mod_charset_lite.so         mod_log_forensic.so    mod_reqtimeout.so
   mod_allowmethods.so     mod_data.so                 mod_logio.so           mod_request.so
   mod_asis.so             mod_dav_fs.so               mod_lua.so             mod_rewrite.so
   mod_auth_basic.so       mod_dav_lock.so             mod_macro.so           mod_sed.so
   mod_auth_digest.so      mod_dav.so                  mod_mime_magic.so      mod_setenvif.so
   ##### snipped

   Each of the configuration file might contain more than one LoadModule directives.