Apache HTTP Server Version 2.4

https://httpd.apache.org/docs/2.4
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### Test the Apache HTTP Server installation

Source: https://httpd.apache.org/docs/2.4/en/install.html

Starts the server using the apachectl control script. The _PREFIX_ placeholder must be replaced with the actual installation prefix.

```bash
$ _PREFIX_/bin/apachectl -k start
```

--------------------------------

### Start an installed httpd service

Source: https://httpd.apache.org/docs/2.4/platform/windows.html

Starts a previously installed httpd service by name.

```bash
httpd.exe -k start -n "MyServiceName"
```

--------------------------------

### Configure, compile, install, customize, and test Apache HTTP Server

Source: https://httpd.apache.org/docs/2.4/en/en/install.html

Commands to configure with a custom prefix, compile, install, edit the configuration file, and start the server. Replace PREFIX with the desired installation path; if not specified, it defaults to /usr/local/apache2.

```bash
$ ./configure --prefix=_PREFIX_
```

```bash
$ make
```

```bash
$ make install
```

```bash
$ vi _PREFIX_/conf/httpd.conf
```

```bash
$ _PREFIX_/bin/apachectl -k start
```

--------------------------------

### Start the Default httpd Instance with service httpd restart

Source: https://httpd.apache.org/docs/2.4/en/en/platform/rpm.html

Starts the default Apache httpd instance after installation. The default configuration is under /etc/httpd, logs go to /var/log/httpd, and the environment is set in /etc/sysconfig/httpd.

```bash
service httpd restart
```

--------------------------------

### Pass additional configure options to config.nice

Source: https://httpd.apache.org/docs/2.4/en/install.html

Pass additional arguments to config.nice to append them to the original configure options. This example sets a custom prefix and port, useful for testing a new version alongside an existing installation.

```bash
$ ./config.nice --prefix=/home/test/apache --with-port=90
```

--------------------------------

### Install httpd with make install

Source: https://httpd.apache.org/docs/2.4/en/en/install.html

Installs the package under the configured installation PREFIX. Typically requires root privileges.

```bash
$ make install
```

--------------------------------

### Install Apache httpd on Ubuntu/Debian

Source: https://httpd.apache.org/docs/2.4/en/install.html

Install and start Apache httpd on Ubuntu or Debian using the system package manager. These commands are for platform packages, which may differ from a source build in configuration layout and defaults.

```bash
sudo apt install apache2
sudo systemctl start apache2
```

--------------------------------

### Compile, install, and reload a sample Apache module with make all reload

Source: https://httpd.apache.org/docs/2.4/en/en/programs/apxs.html

Compiles the generated sample module, installs and activates it, then restarts Apache. The output shows the full build, install, and restart sequence including the debug message confirming the module was loaded.

```shell
$ cd foo
$ make all reload
apxs -c mod_foo.c
/path/to/libtool --mode=compile gcc ... -c mod_foo.c
/path/to/libtool --mode=link gcc ... -o mod_foo.la mod_foo.slo
apxs -i -a -n "foo" mod_foo.la
/path/to/instdso.sh mod_foo.la /path/to/apache/modules
/path/to/libtool --mode=install cp mod_foo.la /path/to/apache/modules
...
chmod 755 /path/to/apache/modules/mod_foo.so
[activating module `foo' in /path/to/apache/conf/httpd.conf]
apachectl restart
/path/to/apache/sbin/apachectl restart: httpd not running, trying to start
[Tue Mar 31 11:27:55 1998] [debug] mod_so.c(303): loaded module foo_module
/path/to/apache/sbin/apachectl restart: httpd started
$ _
```

--------------------------------

### Compile and install mod_example with APXS

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Compiles, installs, and activates the mod_example module using APXS. Assumes the source file is named mod_example.c.

```bash
apxs -i -a -c mod_example.c
```

--------------------------------

### Directory Configuration Example

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

An example of parent and child directory configurations where the child inherits values from the parent.

```apache
<Directory "/var/www">
    ExampleEnabled On
    ExamplePath "/foo/bar"
    ExampleAction file allow
</Directory>
<Directory "/var/www/subdir">
    ExampleAction file deny
</Directory>
```

--------------------------------

### Install development files with gmake

Source: https://httpd.apache.org/docs/2.4/en/en/platform/netware.html

Same as install but also creates a `\lib` and `\include` directory in the destination directory and copies headers and import files.

```makefile
gmake -f nwgnumakefile installdev
```

--------------------------------

### Control httpd service with -k start, stop, shutdown, restart

Source: https://httpd.apache.org/docs/2.4/en/en/platform/windows.html

Control an installed httpd service from the command line. Use -k start to start, -k stop or -k shutdown to stop, and -k restart to restart and force a reread of the configuration file. Always specify the service name with -n.

```command
httpd.exe -k start -n "MyServiceName"
```

```command
httpd.exe -k stop -n "MyServiceName"
```

```command
httpd.exe -k shutdown -n "MyServiceName"
```

```command
httpd.exe -k restart -n "MyServiceName"
```

--------------------------------

### Sample balancer setup with ProxyPass and BalancerMember

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_proxy.html

Sample balancer setup showing ProxyPass with balancer:// scheme, stickysession, nofailover, and BalancerMember directives with loadfactor.

```apache
ProxyPass "/special-area" "http://special.example.com" smax=5 max=10
ProxyPass "/" "balancer://mycluster/" stickysession=JSESSIONID|jsessionid nofailover=On
<Proxy "balancer://mycluster">
    BalancerMember "ajp://1.2.3.4:8009"
    BalancerMember "ajp://1.2.3.5:8009" loadfactor=20
    # Less powerful server, don't send as many requests there,
    BalancerMember "ajp://1.2.3.6:8009" loadfactor=5
</Proxy>
```

--------------------------------

### Configure with custom compiler and modules

Source: https://httpd.apache.org/docs/2.4/en/en/install.html

Example configure command that compiles httpd for the installation tree /sw/pkg/apache with a particular compiler and flags, plus the additional modules mod_ldap and mod_lua. Uses CC and CFLAGS environment variables and --enable-ldap=shared and --enable-lua=shared options.

```bash
$ CC="pgcc" CFLAGS="-O2" \
  ./configure --prefix=/sw/pkg/apache \
  --enable-ldap=shared \
  --enable-lua=shared
```

--------------------------------

### Install Apache with nmake installr or installd

Source: https://httpd.apache.org/docs/2.4/en/en/platform/win_compiling.html

Build and install all Apache files into the directory specified by _dir_. The INSTDIR argument can be omitted to install into the default \Apache22 directory of the current drive.

```bash
nmake /f Makefile.win installr INSTDIR=_dir_
```

```bash
nmake /f Makefile.win installd INSTDIR=_dir_
```

--------------------------------

### Install Apache httpd on Fedora/CentOS/RHEL

Source: https://httpd.apache.org/docs/2.4/en/install.html

Install and start Apache httpd on Fedora, CentOS, or Red Hat Enterprise Linux using the system package manager. These commands are for platform packages, which may differ from a source build in configuration layout and defaults.

```bash
sudo dnf install httpd
sudo systemctl start httpd
```

--------------------------------

### dbmmanage view command example

Source: https://httpd.apache.org/docs/2.4/en/en/programs/dbmmanage.html

Displays the contents of the DBM file. The example displays all records in 'passwords.dat'.

```bash
dbmmanage passwords.dat view
```

--------------------------------

### Install httpd service with custom name and configuration file

Source: https://httpd.apache.org/docs/2.4/platform/windows.html

Installs a specifically named service using a custom configuration file path.

```bash
httpd.exe -k install -n "MyServiceName" -f "c:\files\my.conf"
```

--------------------------------

### AuthBasicProvider example: using dbm provider

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_auth_basic.html

Configuration example for the AuthBasicProvider directive, setting the provider to 'dbm' with an SDBM type and user file. The example is placed inside a <Location> block for the '/secure' path.

```apache
<Location "/secure">
    AuthType basic
    AuthName "private area"
    AuthBasicProvider  dbm
    AuthDBMType        SDBM
    AuthDBMUserFile    "/www/etc/dbmpasswd"
    Require            valid-user
</Location>
```

--------------------------------

### Symlink example: expose root filesystem via public_html

Source: https://httpd.apache.org/docs/2.4/en/en/misc/security_tips.html

Shows a dangerous symlink setup where the root directory is linked into public_html, allowing clients to walk the entire filesystem by accessing http://localhost/~root/. Use this only to understand the risk; the recommended fix is to deny default access and disable UserDir for root.

```text
# cd /; ln -s / public_html   
   Accessing `http://localhost/~root/`
```

--------------------------------

### dbmmanage adduser command example

Source: https://httpd.apache.org/docs/2.4/en/en/programs/dbmmanage.html

Asks for a password and then adds an entry for username to filename. The example adds user 'krietz' to 'passwords.dat'.

```bash
dbmmanage passwords.dat adduser krietz
```

--------------------------------

### Install httpd service with a custom name

Source: https://httpd.apache.org/docs/2.4/platform/windows.html

Installs the httpd service with a specific name to allow multiple service installations.

```bash
httpd.exe -k install -n "MyServiceName"
```

--------------------------------

### Conditional module loading with <IfDefine> and -D parameters

Source: https://httpd.apache.org/docs/2.4/en/en/mod/core.html

Shows how to start httpd with multiple -D parameters and then use nested <IfDefine> blocks to conditionally load modules based on those parameters. The example loads proxy, cache, and mem_cache modules only when the corresponding parameters are defined, and falls back to cache_disk when MemCache is not defined.

```text
httpd -DReverseProxy -DUseCache -DMemCache ...
```

```apache
<IfDefine ReverseProxy>
  LoadModule proxy_module   modules/mod_proxy.so
  LoadModule proxy_http_module   modules/mod_proxy_http.so
  <IfDefine UseCache>
    LoadModule cache_module   modules/mod_cache.so
    <IfDefine MemCache>
      LoadModule mem_cache_module   modules/mod_mem_cache.so
    </IfDefine>
    <IfDefine !MemCache>
      LoadModule cache_disk_module   modules/mod_cache_disk.so
    </IfDefine>
  </IfDefine>
</IfDefine>
```

--------------------------------

### Build and install a distributed module with configure

Source: https://httpd.apache.org/docs/2.4/dso.html

Builds and installs a distributed Apache httpd module (e.g., mod_foo.c) into its own DSO (mod_foo.so). The --prefix option sets the installation directory and --enable-foo enables the module.

```bash
$ ./configure --prefix=/path/to/install --enable-foo
$ make install
```

--------------------------------

### Create directory configuration

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Allocates and initializes a new example_config structure for per-directory contexts. Sets default values: context string, enabled flag to 0, path to empty, and typeOfAction to 0x00.

```c
void *create_dir_conf(apr_pool_t *pool, char *context)
{
    context = context ? context : "Newly created configuration";

    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
    example_config    *cfg = apr_pcalloc(pool, sizeof(example_config));
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/

    if(cfg)
    {
        {
            /* Set some default values */
            strcpy(cfg->context, context);
            cfg->enabled = 0;
            memset(cfg->path, 0, 256);
            cfg->typeOfAction = 0x00;
        }
    }

    return cfg;
}
```

--------------------------------

### Sample configure --help Optional Features

Source: https://httpd.apache.org/docs/2.4/en/en/programs/configure.html

Typical output of ./configure -h or ./configure --help under the Optional Features section. Determine which modules are enabled or disabled by default based on the presence of --disable-* or --enable-* flags.

```text
Optional Features:
  ...
  --disable-example1     example module 1
  --enable-example2      example module 2
  ...
```

--------------------------------

### ProxyDomain directive example

Source: https://httpd.apache.org/docs/2.4/en/mod/mod_proxy.html

Example configuration for ProxyDomain, which sets the default domain for proxied requests in an intranet. The domain must start with a dot. This example also includes ProxyRemote and NoProxy directives, which are part of the same configuration block.

```apache
ProxyRemote  "*"  "http://firewall.example.com:81"
NoProxy         ".example.com" "192.168.112.0/21"
ProxyDomain     ".example.com"
```

--------------------------------

### mod_example example_set_path function

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Handler for the 'examplePath' directive. Copies the argument into conf->path using strcpy.

```c
const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
{
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
    example_config    *conf = (example_config *) cfg;
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/

    if(conf)
    {
        strcpy(conf->path, arg);
    }

    return NULL;
}
```

--------------------------------

### Install httpd as a Windows NT service

Source: https://httpd.apache.org/docs/2.4/platform/windows.html

Installs the httpd service using the default service name and configuration file.

```bash
httpd.exe -k install
```

--------------------------------

### Start Additional httpd Instance with service httpd-additional restart

Source: https://httpd.apache.org/docs/2.4/en/en/platform/rpm.html

Starts the additional httpd instance after configuring its environment and configuration file. Repeat this process for each additional server instance.

```bash
service httpd-additional restart
```

--------------------------------

### Configure the Apache HTTP Server build

Source: https://httpd.apache.org/docs/2.4/en/install.html

Runs the configure script with a custom installation prefix. Replace _PREFIX_ with the desired installation directory.

```bash
$ ./configure --prefix=_PREFIX_
```

--------------------------------

### DNS-01 setup script invocation

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_md.html

Example invocation of the DNS-01 setup script for a wildcard certificate. The script must replace existing TXT records for _acme-challenge.mydomain.com with the provided challenge data.

```bash
/usr/bin/acme-setup-dns setup mydomain.com challenge-data
# this needs to remove all existing DNS TXT records for 
# _acme-challenge.mydomain.com and create a new one with 
# content "challenge-data"
```

--------------------------------

### mod_example configuration directives array

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Defines the configuration directives for mod_example. Uses AP_INIT_TAKE1 for exampleEnabled and examplePath, and AP_INIT_TAKE2 for exampleAction, all with ACCESS_CONF context.

```c
static const command_rec    directives[] =
{
    AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, ACCESS_CONF, "Enable or disable mod_example"),
    AP_INIT_TAKE1("examplePath", example_set_path, NULL, ACCESS_CONF, "The path to whatever"),
    AP_INIT_TAKE2("exampleAction", example_set_action, NULL, ACCESS_CONF, "Special action value!"),
    { }
};
```

--------------------------------

### Create Additional httpd Instance (httpd-additional)

Source: https://httpd.apache.org/docs/2.4/en/platform/rpm.html

Steps to create an additional httpd instance named httpd-additional: create a symlink to the startup script, add it with chkconfig, create an environment file (either copy the template or create a blank one), set OPTIONS to point to the new server root and config file, then start the instance. Repeat for each additional instance.

```bash
ln -s /etc/rc.d/init.d/httpd /etc/rc.d/init.d/httpd-additional
chkconfig --add httpd-additional
```

```bash
# template from httpd
cp /etc/sysconfig/httpd /etc/sysconfig/httpd-additional
```

```bash
# blank template
touch /etc/sysconfig/httpd-additional
```

```bash
OPTIONS="-d /etc/httpd-additional -f conf/httpd-additional.conf"
```

```bash
service httpd-additional restart
```

--------------------------------

### AllowMethods directive example

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_allowmethods.html

Restricts allowed HTTP methods to GET, POST, and OPTIONS for the root location. This is the most common configuration.

```apache
<Location "/">
   AllowMethods GET POST OPTIONS
</Location>
```

--------------------------------

### Configuration to access the example handler

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Adds a Location block to set the handler for the /example path, allowing the module to process requests.

```apache
<Location "/example">
    SetHandler example-handler
</Location>
```

--------------------------------

### SSIStartTag and SSIEndTag configuration

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_include.html

Changes the start and end tags that mod_include uses to mark include elements. The value may not include any whitespace. This example sets the start tag to '<%' and the end tag to '%>', allowing SSI directives with alternate tags.

```apache
SSIStartTag "<%"
SSIEndTag   "%>"
```

--------------------------------

### Script Directive method handling example

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_actions.html

Configures CGI scripts to handle specific HTTP request methods, such as GET and PUT.

```apache
# All GET requests go here
Script GET "/cgi-bin/search"

# A CGI PUT handler
Script PUT "/~bob/put.cgi"
```

--------------------------------

### vhost.map file example

Source: https://httpd.apache.org/docs/2.4/en/rewrite/vhosts.html

Example content for the vhost.map file used in the separate virtual host configuration. It maps customer hostnames to their document root directories.

```plaintext
customer-1.example.com  /www/customers/1  
customer-2.example.com  /www/customers/2  
# ...  
customer-N.example.com  /www/customers/N  
```

--------------------------------

### fcgi authorizer example (partial)

Source: https://httpd.apache.org/docs/2.4/en/mod/mod_authnz_fcgi.html

Perl authorizer for the fcgi authorizer mode of mod_authnz_fcgi. It checks REMOTE_USER, REMOTE_PASSWD, and REQUEST_URI and responds with 200 or 401. The snippet is truncated at the start; the full example appears in the following section, so this partial snippet is incomplete and should be used only as a fragment.

```perl
print STDERR "This text is written to the web server error log.\n";

    if ( ($ENV{'REMOTE_USER' } eq "foo" || $ENV{'REMOTE_USER'} eq "foo1") &&
        $ENV{'REMOTE_PASSWD'} eq "bar" &&
        $ENV{'REQUEST_URI'} =~ m%/bar/.*%) {
        print "Status: 200\n";
        print "Variable-AUTHNZ_1: authnz_01\n";
        print "Variable-AUTHNZ_2: authnz_02\n";
        print "\n";
    }
    else {
        print "Status: 401\n\n";
    }
}
```

--------------------------------

### Apache module configuration functions: example_set_action, create_dir_conf, merge_dir_conf

Source: https://httpd.apache.org/docs/2.4/en/developer/modguide.html

These three functions are part of an Apache module configuration setup. example_set_action handles the 'exampleAction' directive, storing two arguments in a bit-wise manner. create_dir_conf allocates and initializes a new per-directory configuration with defaults. merge_dir_conf merges parent and child configurations, preferring non-default values from the child.

```c
const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
{
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
    example_config    *conf = (example_config *) cfg;
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/

    if(conf)
    {
        {
            if(!strcasecmp(arg1, "file"))
                conf->typeOfAction = 0x01;
            else
                conf->typeOfAction = 0x02;
            if(!strcasecmp(arg2, "deny"))
                conf->typeOfAction += 0x10;
            else
                conf->typeOfAction += 0x20;
        }
    }

    return NULL;
}
```

```c
void *create_dir_conf(apr_pool_t *pool, char *context)
{
    context = context ? context : "Newly created configuration";

    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
    example_config    *cfg = apr_pcalloc(pool, sizeof(example_config));
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/

    if(cfg)
    {
        {
            /* Set some default values */
            strcpy(cfg->context, context);
            cfg->enabled = 0;
            memset(cfg->path, 0, 256);
            cfg->typeOfAction = 0x00;
        }
    }

    return cfg;
}
```

```c
void *merge_dir_conf(apr_pool_t *pool, void *BASE, void *ADD)
{
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
    example_config    *base = (example_config *) BASE;
    example_config    *add = (example_config *) ADD;
    example_config    *conf = (example_config *) create_dir_conf(pool, "Merged configuration");
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/

    conf->enabled = (add->enabled == 0) ? base->enabled : add->enabled;
    conf->typeOfAction = add->typeOfAction ? add->typeOfAction : base->typeOfAction;
    strcpy(conf->path, strlen(add->path) ? add->path : base->path);
    return conf;
}
```

--------------------------------

### Set and get Inter-VM variables with r:ivm_set and r:ivm_get

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_lua.html

Sets and gets Inter-VM variables that persist across VM instances. The example shows a getter/setter that caches data globally, with a note that values are stored per process and should only be used if MaxConnectionsPerChild > 0.

```lua
r:ivm_set("key", value) -- Set an Inter-VM variable to hold a specific value.
                        -- These values persist even though the VM is gone or not being used,
                        -- and so should only be used if MaxConnectionsPerChild is > 0
                        -- Values can be numbers, strings and booleans, and are stored on a 
                        -- per process basis (so they won't do much good with a prefork mpm)
                        
r:ivm_get("key")        -- Fetches a variable set by ivm_set. Returns the contents of the variable
                        -- if it exists or nil if no such variable exists.
                        
-- An example getter/setter that saves a global variable outside the VM:
function handle(r)
    -- First VM to call this will get no value, and will have to create it
    local foo = r:ivm_get("cached_data")
    if not foo then
        foo = do_some_calcs() -- fake some return value
        r:ivm_set("cached_data", foo) -- set it globally
    end
    r:puts("Cached data is: ", foo)
end
```

--------------------------------

### LoadFile directive example

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_so.html

Links in the named object file or library when the server is started or restarted. The filename is either an absolute path or relative to ServerRoot.

```apache
LoadFile "libexec/libxmlparse.so"
```

--------------------------------

### Install the httpd RPM with rpm -U

Source: https://httpd.apache.org/docs/2.4/en/en/platform/rpm.html

Installs the core httpd RPM, which is the only package needed for a basic server. Self-contained modules are included; modules with external dependencies are separate RPMs.

```bash
rpm -U httpd-2.4.x-1.i686.rpm
```

--------------------------------

### Conditional configuration with <IfDefine>

Source: https://httpd.apache.org/docs/2.4/en/en/sections.html

Applies the enclosed directives only when the server is started with the -DClosedForNow command-line parameter. In this example, all requests are redirected to another site when the condition is true.

```apache
<IfDefine ClosedForNow>
    Redirect "/" "http://otherserver.example.com/"
</IfDefine>
```

--------------------------------

### SSLRandomSeed directive example

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_ssl.html

Configure PRNG seeding sources for mod_ssl. Use 'startup' context for initialization and 'connect' for per-connection seeding. The example shows builtin, file, and exec sources with optional byte counts.

```apache
SSLRandomSeed startup builtin
SSLRandomSeed startup "file:/dev/random"
SSLRandomSeed startup "file:/dev/urandom" 1024
SSLRandomSeed startup "exec:/usr/local/bin/truerand" 16
SSLRandomSeed connect builtin
SSLRandomSeed connect "file:/dev/random"
SSLRandomSeed connect "file:/dev/urandom" 1024
```

--------------------------------

### Configuration example for mod_authn_dbd with caching

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_authn_dbd.html

Shows a complete configuration for using mod_authn_dbd with PostgreSQL, including mod_dbd settings, authentication provider setup, and the SQL query for user authentication. The example places socache before dbd in AuthBasicProvider to enable caching, and includes AuthnCacheProvideFor and AuthnCacheContext directives required for caching.

```apache
# mod_dbd configuration
# UPDATED to include authentication caching
DBDriver pgsql
DBDParams "dbname=apacheauth user=apache password=xxxxxx"

DBDMin  4
DBDKeep 8
DBDMax  20
DBDExptime 300

<Directory "/usr/www/myhost/private">
  # mod_authn_core and mod_auth_basic configuration
  # for mod_authn_dbd
  AuthType Basic
  AuthName "My Server"

  # To cache credentials, put socache ahead of dbd here
  AuthBasicProvider socache dbd

  # Also required for caching: tell the cache to cache dbd lookups!
  AuthnCacheProvideFor dbd
  AuthnCacheContext my-server

  # mod_authz_core configuration
  Require valid-user

  # mod_authn_dbd SQL query to authenticate a user
  AuthDBDUserPWQuery "SELECT password FROM authn WHERE user = %s"
</Directory>
```

--------------------------------

### httpd.conf directives for mod_example

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Example httpd.conf directives to override the hard-coded configuration. Sets ExampleEnabled to On, ExamplePath to "/usr/bin/foo", and ExampleAction to file allow.

```apache
ExampleEnabled On
ExamplePath "/usr/bin/foo"
ExampleAction file allow
```

--------------------------------

### Get directory entries

Source: https://httpd.apache.org/docs/2.4/mod/mod_lua.html

Returns a table with all directory entries. The example iterates over the directory entries, stats each file, and prints its type, modification time, size, and name.

```lua
function handle(r)
  local dir = r.context_document_root
  for _, f in ipairs(r:get_direntries(dir)) do
    local info = r:stat(dir .. "/" .. f)
    if info then
      local mtime = os.date(fmt, info.mtime / 1000000)
      local ftype = (info.filetype == 2) and "[dir] " or "[file]"
      r:puts( ("%s %s %10i %s\n"):format(ftype, mtime, info.size, f) )
    end
  end
end
```

--------------------------------

### Get file info with r:stat

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_lua.html

Runs stat() on a file and returns a table with file information. The example checks if a file exists and prints its last modified time.

```lua
r:stat(filename [,wanted]) -- Runs stat() on a file, and returns a table with file information:

local info = r:stat("/var/www/foo.txt")
if info then
    r:puts("This file exists and was last modified at: " .. info.modified)
end
```

--------------------------------

### Group Directive Example

Source: https://httpd.apache.org/docs/2.4/en/mod/mod_unixd.html

Sets the group under which the server will answer requests. The server must be started as root for this directive to take effect; otherwise it will continue running as the original user's group.

```apache
Group www-group
```

--------------------------------

### Order Allow,Deny example: allow example.org except foo subdomain

Source: https://httpd.apache.org/docs/2.4/en/mod/mod_access_compat.html

Allows hosts in example.org except those in foo.example.org, which are denied. Hosts not in example.org are denied by default because the Order is Allow,Deny.

```apache
Order Allow,Deny
Allow from example.org
Deny from foo.example.org
```

--------------------------------

### Server configuration setting Options and AllowOverride

Source: https://httpd.apache.org/docs/2.4/en/en/mod/core.html

Sets the server-level options and the AllowOverride permitted list. Used as the starting point for the example that shows how a .htaccess file can only enable options in the permitted list.

```apache
Options Indexes FollowSymLinks ExecCGI
AllowOverride Options=Indexes
```

--------------------------------

### example_set_action handler for exampleAction directive

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Handler for the "exampleAction" directive. Takes two arguments (file or db, and deny or allow) and stores them in a bit-wise manner in config.typeOfAction. Returns NULL on success.

```c
const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
{
    if(!strcasecmp(arg1, "file")) config.typeOfAction = 0x01;
    else config.typeOfAction = 0x02;
    
    if(!strcasecmp(arg2, "deny")) config.typeOfAction += 0x10;
    else config.typeOfAction += 0x20;
    return NULL;
}
```

--------------------------------

### Overlapping Listen error message

Source: https://httpd.apache.org/docs/2.4/bind.html

Example error message that appears when overlapping Listen directives cause a fatal error, preventing the server from starting. This indicates a binding conflict on the specified address and port.

```text
(48)Address already in use: make_sock: could not bind to address [::]:80
```

--------------------------------

### AddHandler for .example files in .htaccess

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_example_hooks.html

Alternative activation using a .htaccess file. Requests for files with the .example extension in that directory will trigger the example-hooks-handler.

```apache
AddHandler example-hooks-handler ".example"
```

--------------------------------

### Reverse proxy configuration with ProxyPassReverse

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_proxy.html

Example configuration for a reverse proxy setup. It shows how to use ProxyPass, ProxyPassReverse, ProxyPassReverseCookieDomain, and ProxyPassReverseCookiePath together to rewrite redirects and cookies so that clients stay on the proxy host.

```apache
ProxyPass         "/mirror/foo/" "http://backend.example.com/"
ProxyPassReverse  "/mirror/foo/" "http://backend.example.com/"
ProxyPassReverseCookieDomain  "backend.example.com"  "public.example.com"
ProxyPassReverseCookiePath  "/"  "/mirror/foo/"
```

--------------------------------

### List directory entries with r:get_direntries

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_lua.html

Returns a table with all directory entries. The example iterates over the document root, gets file info, and prints formatted output with type, modification time, size, and name.

```lua
r:get_direntries(dir) -- Returns a table with all directory entries.

function handle(r)
  local dir = r.context_document_root
  for _, f in ipairs(r:get_direntries(dir)) do
    local info = r:stat(dir .. "/" .. f)
    if info then
      local mtime = os.date(fmt, info.mtime / 1000000)
      local ftype = (info.filetype == 2) and "[dir] " or "[file]"
      r:puts( ("%s %s %10i %s\n"):format(ftype, mtime, info.size, f) )
    end
  end
end
```

--------------------------------

### Example of requests leading to HTTP 501 with LenientMethods mode

Source: https://httpd.apache.org/docs/2.4/mod/core.html

Shows two requests: one with an unknown HTTP method (WOW) and one with a lowercase method (get). Both trigger a 501 response when LenientMethods mode is used.

```http
# Unknown HTTP method
         WOW / HTTP/1.0


         # Lowercase HTTP method
         get / HTTP/1.0


```

--------------------------------

### Directory container example

Source: https://httpd.apache.org/docs/2.4/en/en/sections.html

Shows how to apply directives to a filesystem directory and its subdirectories using the <Directory> container.

```apache
<Directory /usr/local/apache2/htdocs>
    Options Indexes FollowSymLinks
</Directory>
```

--------------------------------

### ProxyPassReverseCookiePath example

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_proxy.html

Rewrites a cookie path from the backend path "/" (or any path starting with it) to "/mirror/foo/" in Set-Cookie headers. Use with ProxyPassReverse when backend URL paths are mapped to public paths on the reverse proxy.

```apache
ProxyPassReverseCookiePath  "/"  "/mirror/foo/"
```

--------------------------------

### Build Apache for NetWare with nwgnumakefile

Source: https://httpd.apache.org/docs/2.4/platform/netware.html

Build Apache for NetWare using the provided makefile. First run the prebuild target to create the nwprebuild directory and copy required utilities, then run GENCHARS.nlm and DFTABLES.nlm on a NetWare server to generate test_char.h and chartables.c, copy those files to \httpd-2.0\os\netware, and finally run gmake -f nwgnumakefile (optionally with install) to build and create a distribution.

```shell
gmake -f nwgnumakefile prebuild
```

```shell
             SYS:\genchars > sys:\test_char.h  
             SYS:\dftables sys:\chartables.c  
 
```

```shell
gmake -f nwgnumakefile install
```

--------------------------------

### mod_example example_set_enabled function

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Handler for the 'exampleEnabled' directive. Sets conf->enabled to 1 if the argument is 'on' (case-insensitive), otherwise sets it to 0.

```c
const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
{
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
    example_config    *conf = (example_config *) cfg;
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/

    if(conf)
    {
        if(!strcasecmp(arg, "on"))
            conf->enabled = 1;
        else
            conf->enabled = 0;
    }

    return NULL;
}
```

--------------------------------

### Lua handler function for mod_lua

Source: https://httpd.apache.org/docs/2.4/en/mod/mod_lua.html

Example Lua handler for mod_lua that responds to GET, POST, and PUT methods. It sets the content type to text/plain, prints the URI or form-encoded arguments, and returns appropriate status codes for unsupported methods.

```lua
**example.lua**  
-- example handler

require "string"

--[[
     This is the default method name for Lua handlers, see the optional
     function-name in the LuaMapHandler directive to choose a different
     entry point.
--]]
function handle(r)
    r.content_type = "text/plain"

    if r.method == 'GET' then
        r:puts("Hello Lua World!\n")
        for k, v in pairs( r:parseargs() ) do
            r:puts( string.format("%s: %s\n", k, v) )
        end
    elseif r.method == 'POST' then
        r:puts("Hello Lua World!\n")
        for k, v in pairs( r:parsebody() ) do
            r:puts( string.format("%s: %s\n", k, v) )
        end
    elseif r.method == 'PUT' then
-- use our own Error contents
        r:puts("Unsupported HTTP method " .. r.method)
        r.status = 405
        return apache2.OK
    else
-- use the ErrorDocument
        return 501
    end
    return apache2.OK
end
```

--------------------------------

### Trace: brk heap allocation

Source: https://httpd.apache.org/docs/2.4/en/en/misc/perf-tuning.html

Shows heap allocation via brk. These calls are rare because the httpd uses custom memory allocators (apr_pool and apr_bucket_alloc) for most request processing; here the httpd has just started and must call malloc to get raw memory for those allocators.

```text
/65:    brk(0x002170E8)                                 = 0
/65:    brk(0x002190E8)                                 = 0
```

--------------------------------

### Handler for the exampleAction directive

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Sets a bit-wise action based on two arguments: first 'file' or 'db', second 'deny' or 'allow'. Stores the result in conf->typeOfAction.

```c
const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
{
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
    example_config    *conf = (example_config *) cfg;
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/

    if(conf)
    {
        {
            if(!strcasecmp(arg1, "file"))
                conf->typeOfAction = 0x01;
            else
                conf->typeOfAction = 0x02;
            if(!strcasecmp(arg2, "deny"))
                conf->typeOfAction += 0x10;
            else
                conf->typeOfAction += 0x20;
        }
    }

    return NULL;
}
```

--------------------------------

### mod_example example_handler function

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Handles requests for the 'example-handler' handler. Retrieves the module configuration, sets content type to text/plain, and outputs the configuration values.

```c
static int example_handler(request_rec *r)
{
    if(!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);

    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/
    example_config    *config = (example_config *) ap_get_module_config(r->per_dir_config, &example_module);
    /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/

    ap_set_content_type(r, "text/plain");
    ap_rprintf(r, "Enabled: %u\n", config->enabled);
    ap_rprintf(r, "Path: %s\n", config->path);
    ap_rprintf(r, "TypeOfAction: %x\n", config->typeOfAction);
    ap_rprintf(r, "Context: %s\n", config->context);
    return OK;
}
```

--------------------------------

### SetEnvIf examples for request attributes

Source: https://httpd.apache.org/docs/2.4/en/mod/mod_setenvif.html

Sets environment variables based on request attributes. The first three set object_is_image for image requests, the fourth sets intra_site_referral for matching referers, and the last sets HAVE_TS when a header beginning with TS has a value starting with a lowercase letter.

```apache
SetEnvIf Request_URI "\.gif$" object_is_image=gif
SetEnvIf Request_URI "\.jpg$" object_is_image=jpg
SetEnvIf Request_URI "\.xbm$" object_is_image=xbm
    
SetEnvIf Referer www\.mydomain\.example\.com intra_site_referral
    
SetEnvIf object_is_image xbm XBIT_PROCESSING=1
    
SetEnvIf Request_URI "\.(.*)$" EXTENSION=$1

SetEnvIf ^TS  ^[a-z]  HAVE_TS
```

--------------------------------

### Complete mod_example_config_simple.c module

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Complete Apache module source file (mod_example_config_simple.c) that assembles the configuration structure, directive handlers, command_rec table, module handler, hook registration, and module declaration. Includes default configuration values set in register_hooks.

```c
/* mod_example_config_simple.c: */
#include <stdio.h>
#include "apr_hash.h"
#include "ap_config.h"
#include "ap_provider.h"
#include "httpd.h"
#include "http_core.h"
#include "http_config.h"
#include "http_log.h"
#include "http_protocol.h"
#include "http_request.h"

/*
 ==============================================================================
 Our configuration prototype and declaration:
 ==============================================================================
 */
typedef struct {
    int         enabled;      /* Enable or disable our module */
    const char *path;         /* Some path to...something */
    int         typeOfAction; /* 1 means action A, 2 means action B and so on */
} example_config;

static example_config config;

/*
 ==============================================================================
 Our directive handlers:
 ==============================================================================
 */
/* Handler for the "exampleEnabled" directive */
const char *example_set_enabled(cmd_parms *cmd, void *cfg, const char *arg)
{
    if(!strcasecmp(arg, "on")) config.enabled = 1;
    else config.enabled = 0;
    return NULL;
}

/* Handler for the "examplePath" directive */
const char *example_set_path(cmd_parms *cmd, void *cfg, const char *arg)
{
    config.path = arg;
    return NULL;
}

/* Handler for the "exampleAction" directive */
/* Let's pretend this one takes one argument (file or db), and a second (deny or allow), */
/* and we store it in a bit-wise manner. */
const char *example_set_action(cmd_parms *cmd, void *cfg, const char *arg1, const char *arg2)
{
    if(!strcasecmp(arg1, "file")) config.typeOfAction = 0x01;
    else config.typeOfAction = 0x02;
    
    if(!strcasecmp(arg2, "deny")) config.typeOfAction += 0x10;
    else config.typeOfAction += 0x20;
    return NULL;
}

/*
 ==============================================================================
 The directive structure for our name tag:
 ==============================================================================
 */
static const command_rec        example_directives[] =
{
    AP_INIT_TAKE1("exampleEnabled", example_set_enabled, NULL, RSRC_CONF, "Enable or disable mod_example"),
    AP_INIT_TAKE1("examplePath", example_set_path, NULL, RSRC_CONF, "The path to whatever"),
    AP_INIT_TAKE2("exampleAction", example_set_action, NULL, RSRC_CONF, "Special action value!"),
    { }
};
/*
 ==============================================================================
 Our module handler:
 ==============================================================================
 */
static int example_handler(request_rec *r)
{
    if(!r->handler || strcmp(r->handler, "example-handler")) return(DECLINED);
    ap_set_content_type(r, "text/plain");
    ap_rprintf(r, "Enabled: %u\n", config.enabled);
    ap_rprintf(r, "Path: %s\n", config.path);
    ap_rprintf(r, "TypeOfAction: %x\n", config.typeOfAction);
    return OK;
}

/*
 ==============================================================================
 The hook registration function (also initializes the default config values):
 ==============================================================================
 */
static void register_hooks(apr_pool_t *pool) 
{
    config.enabled = 1;
    config.path = "/foo/bar";
    config.typeOfAction = 3;
    ap_hook_handler(example_handler, NULL, NULL, APR_HOOK_LAST);
}
/*
 ==============================================================================
 Our module name tag:
 ==============================================================================
 */
module AP_MODULE_DECLARE_DATA   example_module =
{
    STANDARD20_MODULE_STUFF,
    NULL,               /* Per-directory configuration handler */
    NULL,               /* Merge handler for per-directory configurations */
    NULL,               /* Per-server configuration handler */
    NULL,               /* Merge handler for per-server configurations */
    example_directives, /* Any directives we may have for httpd */
    register_hooks,     /* Our hook registering function */
    AP_MODULE_FLAG_NONE  /* Flags */
};
```

--------------------------------

### DirectorySlash Off - Disable trailing slash redirect with security warning

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_dir.html

Disables the trailing slash redirect for a specific location. The comment warns of security implications, and the example includes a SetHandler directive. Turning off the redirect may result in information disclosure, and some browsers may change POST requests to GET.

```apache
# see security warning below!
<Location "/some/path">
    DirectorySlash Off
    SetHandler some-handler
</Location>

```

--------------------------------

### Example DocumentRoot with IP address in UNC path

Source: https://httpd.apache.org/docs/2.4/en/en/platform/windows.html

Shows how to set DocumentRoot to a UNC path using an IP address. Use this when the network resource is identified by an IP address.

```apache
UNCList 192.168.1.50
  DocumentRoot "//192.168.1.50/docs/"
```

--------------------------------

### Create and Register an Additional httpd Instance

Source: https://httpd.apache.org/docs/2.4/en/en/platform/rpm.html

Creates a symbolic link to the startup script for an additional server instance named httpd-additional and registers it with chkconfig. The startup script uses its own name to find the environment file and server root.

```bash
ln -s /etc/rc.d/init.d/httpd /etc/rc.d/init.d/httpd-additional
chkconfig --add httpd-additional
```

--------------------------------

### example_config struct definition

Source: https://httpd.apache.org/docs/2.4/developer/modguide.html

Defines the example_config structure with fields for context, path, typeOfAction, and enabled. This is the modified version used for tracking which context configuration is being used.

```c
typedef struct {
    char        context[256];
    char        path[256];
    int         typeOfAction;
    int         enabled;
} example_config;
```

--------------------------------

### Start and stop Apache with apachectl

Source: https://httpd.apache.org/docs/2.4/en/en/install.html

Starts the Apache HTTP Server with apachectl -k start, then stops it with apachectl -k stop. After starting, you can request your first document via http://localhost/.

```bash
$ _PREFIX_/bin/apachectl -k start
```

```bash
$ _PREFIX_/bin/apachectl -k stop
```

--------------------------------

### Compile mod_example with apxs

Source: https://httpd.apache.org/docs/2.4/en/developer/modguide.html

Command to compile the example module using apxs. Run from the module's source directory.

```bash
$ apxs -c -i -a mod_example.c
```

--------------------------------

### Require method GET POST OPTIONS

Source: https://httpd.apache.org/docs/2.4/en/mod/mod_authz_core.html

Allows only GET, HEAD, POST, and OPTIONS requests. GET and HEAD are treated as equivalent; TRACE is not available.

```apache
Require method GET POST OPTIONS
```

--------------------------------

### Install httpd Windows service with httpd.exe -k install

Source: https://httpd.apache.org/docs/2.4/en/en/platform/windows.html

Install httpd as a Windows NT service. The first command installs the service with the default name Apache2.4 and configuration conf\httpd.conf. Use the -n option to specify a custom service name, and -f to specify a custom configuration file.

```command
httpd.exe -k install
```

```command
httpd.exe -k install -n "MyServiceName"
```

```command
httpd.exe -k install -n "MyServiceName" -f "c:\files\my.conf"
```

--------------------------------

### Example Alias and corresponding Directory with UNC path

Source: https://httpd.apache.org/docs/2.4/en/en/platform/windows.html

Shows how to configure Alias directives with UNC paths and corresponding Directory blocks for multiple image hosts. Use this to serve images from network shares.

```apache
UNCList imagehost1 imagehost2
Alias "/images/" "//imagehost/www/images/"
Alias "/images2/" "//imagehost2/www/images/"

<Directory "//imagehost/www/images/">
#...
</Directory>
<Directory "//imagehost2/www/images/">
#...
</Directory>
```

--------------------------------

### CacheEnable examples for various URL patterns

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_cache.html

Shows how to use CacheEnable with Location, LocationMatch, and global directives to cache specific paths, regex matches, and forward proxy URLs. The first two examples require CacheQuickHandler off, while the global ones work with both normal and quick handlers.

```apache
# Cache content (normal handler only)
CacheQuickHandler off
<Location "/foo">
    CacheEnable disk
</Location>

# Cache regex (normal handler only)
CacheQuickHandler off
<LocationMatch "foo$">
    CacheEnable disk
</LocationMatch>

# Cache all but forward proxy url's (normal or quick handler)
CacheEnable  disk  /

# Cache FTP-proxied url's (normal or quick handler)
CacheEnable  disk  ftp://

# Cache forward proxy content from www.example.org (normal or quick handler)
CacheEnable  disk  http://www.example.org/
```

--------------------------------

### Get HTTP cookie with r:getcookie

Source: https://httpd.apache.org/docs/2.4/en/en/mod/mod_lua.html

Gets an HTTP cookie by key.

```lua
r:getcookie(key) -- Gets a HTTP cookie
```
Tokens:
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