New Features in Apache v2 (Apache: The Definitive Guide, 3rd Edition)

1.11. New Features in Apache v2

The procedure for configuring and compiling Apache has changed, as we will see later.

High-level decisions about the way Apache works internally can now be made at compile time by including one of a series of Multi Processing Modules (MPMs). This is done by attaching a flag to configure:

./configure <other flags> --with_mpm=<name of MPM>

Although MPMs are rather like ordinary modules, only one can be used at a time. Some of them are designed to adapt Apache to different operating systems; others offer a range of different optimizations for Unix.

It will be shown, along with the other compiled-in modules, by executing httpd -l. When we went to press, these were the possible MPMs under Unix:

prefork: Default. Most closely imitates behavior of v1.3. Currently the default for Unix and sites that require stability, though we hope that threading will become the default later on.
threaded: Suitable for sites that require the benefits brought by threading, particularly reduced memory footprint and improved interthread communications. But see "prefork" earlier in this list.
perchild: Allows different hosts to have different user IDs.
mpmt_pthread: Similar to prefork, but each child process has a specified number of threads. It is possible to specify a minimum and maximum number of idle threads.
Dexter: Multiprocess, multithreaded MPM that allows you to specify a static number of processes.
Perchild: Similar to Dexter, but you can define a seperate user and group for each child process to increase server security.

Other operating systems have their own MPMs:

spmt_os2: For OS2.
beos: For the Be OS.
WinNT: Win32-specific version, taking advantage of completion ports and native function calls to give better network performance.

To begin with, accept the default MPM. More advanced users should refer to http://httpd.apache.org/docs-2.0/mpm.html and http://httpd.apache.org/docs-2.0/misc/perf-tuning.html.

See the entry for the AcceptMutex directive in Chapter 3.

1.11.1. Config File Changes in v2

Version 2.0 makes the following changes to the Config file:

CacheNegotiatedDocs now takes the argument on/off. Existing instances of CacheNegotiatedDocs should be given the argument on.
ErrorDocument <HTTP error number> "<message>" now needs quotes around the <message>, not just at the start.
The AccessConfig and ResourceConfig directives have been abolished. If you want to use these files, replace them by Include conf/srm.conf Include conf/access.confin that order, and at the end of the Config file.
The BindAddress directive has been abolished. Use Listen.
The ExtendedStatus directive has been abolished.
The ServerType directive has been abolished.
The AgentLog, ReferLog, and ReferIgnore directives have been removed along with the mod_log_agent and mod_log_referer modules. Agent and referer logs are still available using the CustomLog directive.
The AddModule and ClearModule directives have been abolished. A very useful point is that Apache v2 does not care about the order in which DSOs are loaded.

1.11.2. httpd Command-Line Changes

Running the v2 httpd with the flag -h to show the possible command-line flags produces this:

Usage: ./httpd [-D name] [-d directory] [-f file]
               [-C "directive"] [-c "directive"]
               [-v] [-V] [-h] [-l] [-L] [-t] [-T]
Options:
  -D name           : define a name for use in <IfDefine name> directives
  -d directory      : specify an alternate initial ServerRoot
  -f file           : specify an alternate ServerConfigFile
  -C "directive"    : process directive before reading config files
  -c "directive"    : process directive after reading config files
  -v                : show version number
  -V                : show compile settings
  -h                : list available command line options (this page)
  -l                : list compiled in modules
  -L                : list available configuration directives
  -t -D DUMP_VHOSTS : show parsed settings (currently only vhost settings)
  -t                : run syntax check for config files (with docroot check)
  -T                : run syntax check for config files (without docroot check)

In particular, the -X flag has been removed. You can get the same effect — running a single copy of Apache without any children being generated — with this:

httpd -D ONE_PROCESS

or:

httpd -D NO_DETACH

depending on the MPM used. The available flags for each MPM will be visible on running httpd with -?.

1.11.3. Module Changes in v2

Version 2.0 makes the following changes to module handling:

mod_auth_digest is now a standard module in v2.

mod_mmap_static, which was experimental in v1.3, has been replaced by mod_file_cache.

Third-party modules written for Apache v1.3 will not work with v2 since the API has been completely rewritten. See Chapter 20 and Chapter 21.