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Administratorís E-Mail Address - Apache

Learn the basic steps necessary to download, install, and configure a basic Apache server. This article is from chapter two of Pro Apache by Peter Wainwright. (Apress, 2004, ISBN: 1590593006).

TABLE OF CONTENTS:
  1. Getting Started with Apache
  2. Installing Apache
  3. Installing Apache from Binary Distribution
  4. Installing Apache from Prebuilt Packages
  5. Installing Apache by Hand
  6. Upgrading Apache
  7. Basic Configuration
  8. Administratorís E-Mail Address
  9. Starting, Stopping, and Restarting the Server
  10. Generic Invocation Options
  11. Windows-Specific Invocation Options
  12. Testing the Server
  13. Testing the Server Configuration Without Starting It
  14. Using Graphical Configuration Tools
By: Apress Publishing
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December 13, 2004

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Usually when running a Web site, youíll want an e-mail contact address so that people can report problems to you. In fact, Apache uses the administratorís e-mail address in its default error messages when problems are encountered. The e-mail address is set with the ServerAdmin directive and can be any valid e-mail address; it isnít restricted to the same domain name as the Web server, for example:

ServerAdmin administrator@someotherdomain.net

However, for this site, youíll use the same domain as the Web site:

ServerAdmin webmaster@alpha-complex.com

Note that you donít specify the hostname www in the e-mail addressóremember, www.alpha-complex.com refers to the machine running Apache, not necessarily the machine running your mail server. Even if both are on the same machine, you may decide to separate them later, so itís best to use a generic address from the start. Having said this, itís true that a mail exchanger can be set up in the DNS to direct e-mail to the www address to a different server, if thatís what you want to do.

Server Root

The server root is where Apache keeps all its essential files and is the default root for Apacheís other directives to append to if theyíre defined with a relative pathósee the following error log and document root sections for two good examples. Youíll stick with the default for now:

ServerRoot /usr/local/apache

Default Error Log

Apache can support many different kinds of logs, of which the most common are an access log (also called a transfer log), referrer log, and error log. You might not want to bother with access and referrer logs because they take up space and processing time, but you certainly want an error log. Apache sets the error log name with the ErrorLog directive, which defaults to logs/error_log under Unix and logs/error.log for Windows and OS/2. The name of the error log is either an explicit pathname starting with / or a name relative to the server root. To put the error log explicitly in the default place under the server root, you could specify this:

ErrorLog /usr/local/apache/logs/error_log

However, more simply, and with the same effect, you can use this:

ErrorLog logs/error_log

Because youíll probably want a transfer log (also called an access log) at some point, you can take care of it at the same time and worry about customizing it to your own requirements later:

TransferLog logs/access_log

If you want to allow for virtual hosts, you might also place per-host versions of these files in a directory related to the domain name of the Web site, alongside a document root, which is the last location you need to set.

Document Root

Last, but not least, you need to decide where the actual Web pages will reside. This can be any valid directory accessible to the server, even on another computer over NT File System (NFS) or Server Message Block (SMB), though this would be very inefficient unless youíre using a dedicated NFS system such as a NetApp filer (see http://www.netapp.com/products/filer/). As Chapter 8 discusses, there are additional considerations if the document root isnít local, so youíll assume it is for now.

By default, Apache looks for a directory called htdocs under the server root. If you want to change it, you can specify either a relative path, which Apache will look for under the server root, or an absolute path, which can be outside it. Itís quite usual for the document root to be moved somewhere else to distance the publicly accessible Web site or Web sites from any sensitive Apache configuration files. This also makes upgrading or replacing the Apache installation simpler. So to specify the default document root, either of the following will do:

DocumentRoot htdocs
DocumentRoot /usr/local/apache/htdocs

For your server, youíre going to place your Web site in its own directory inside a directory called www well outside the server root in /home:

DocumentRoot /home/www/alpha-complex/web

This naming scheme will serve you well if you decide to host multiple Web sites, as you can then add more directories under /home/www.

As suggested previously, you can also use this directory to store log files, CGI scripts, and other files related to the Web site that donít go into the document root itself, as these alternative log directives illustrate:

TransferLog /home/www/alpha-complex/logs/access_log
ErrorLog /home/www/alpha-complex/logs/error_log

Introducing the Master Configuration File

Now that youíve decided on your basic configuration choices, you need to make the necessary changes to Apacheís configuration. Originally, Apache came with three configuration files:

  • httpd.conf

  • access.conf

  • srm.conf

Since Apache 1.3.4 was released, only httpd.conf is now necessary, and the other two have been merged into it. Apache 2 removes support for them entirely, so youíll make all your changes in httpd.conf.

Taking all the decisions youíve made, you arrive at the basic configuration for your example server, and the httpd.conf file now will look like this:

ServerName www.alpha-complex.com
Listen 192.168.1.1:80
Listen 192.168.1.1:443
User nobody
Group nobody
ServerAdmin webmaster@alpha-complex.com
#ServerRoot /usr/local/apache
#ErrorLog logs/error_log
TransferLog logs/access_log
DocumentRoot /home/www/alpha-complex

The lines prefixed with a hash are commented outótheyíre the defaults anyway, so theyíre here only to remind you of what they are. Windows Apache doesnít understand the User and Group directives, but itís smart enough to just ignore them rather stopping with an error.

As it happens, all these directives are documented in httpd.conf, even in a three-file configuration, so setting these directives (uncommenting the ones you want to change if theyíre commented) is a one-step operationóyou simply need to uncomment if theyíre commented. Once httpd.conf has been changed and saved back to the disk, youíre ready to go.

NOTE Iím listing only the configuration directives youíre actually changing because the Apache configuration file is long and contains a great deal of information. You want to keep all of it for the moment, so youíll see only the things you need to for now.

Other Basic Configuration Directives

Although not usually part of a basic Apache installation, Apache does support a few other directives that control the location of certain files created by Apache during its execution. Because most of them are both somewhat technical and rarely need to be changed from the default setting, I mention them here for completeness. However, if youíre going to use them at all, this is the time and place to do it. Note that all of these directives are specific to Unix.

The PidFile directive determines the name and location of the file in which Apache stores the process ID of the parent Apache process. This is the process ID that can be sent signals to stop or restart the server, for example, to send a termination signal:

$ kill -TERM `cat /usr/local/apache/logs/httpd.pid`

TERM is the default signal for the kill command, so you donít need to state it explicitly. Use kill -l to see a list of the available signal names, though Apache would recognize TERM, HUP, and USR1 only.

Iíll discuss the subject of starting and stopping Apache in more detail in a moment. The default value of PidFile is logs/httpd.pid, which places the file in the logs directory under the server root. Like all Apacheís Location directives, an absolute pathname can also be used to specify a location outside of the server root. For example, Apache packages often move the PidFile to /var/run with this:

PidFile /var/run/httpd.pid

The LockFile directive determines the name and location of the file that Apache uses for synchronizing the allocation of new network requests. In Apache 1.3, this is a compile-time setting. In Apache 2, the AcceptMutex directive determines how Apache handles synchronization, and the lock file is used only if itís set to the values fcntl or flock. For platforms that donít support any kind of in-memory lock, this directive can be used to move the lock file from the default of logs/accept.lock. This is necessary if the logs directory is on another server and is mounted via NFS or SMB because the lock file must be on a local file system. Youíll also need to do this if you want to run more than one Apache server, for example:

LockFile /usr/local/apache/logs/server2.lock

NOTE See Chapter 8 for a full discussion of Apacheís locking mechanism and how the different lock types affect performance.

The ScoreBoardFile directive determines the location of a file required on some platforms for the parent Apache process to communicate with child processes. Like the access lock, Apache will usually create the scoreboard in memory (technically, a shared memory segment), but not all platforms can support this. To find out if a given Apache binary needs a scoreboard file, simply run Apache and see if the file named by the ScoreBoardFile directive appears. The default value is logs/apache_status, which places the file in the logs directory under the server root. Administrators concerned about speed might want to move the scoreboard to a Random Access Memory (RAM) disk, which will improve Apacheís performance, for example:

ScoreBoardFile /mnt/ramdisk/apache_status

This assumes that a RAM disk is present and mounted on /mnt/ramdisk, of course. Keep in mind that if you want to run more than one Apache server, the servers need to use different scoreboard files. A more ideal solution would be to migrate to a platform that allows Apache to store the scoreboard in memory in the first place.

In modern versions of Apache (1.3.28 onward), the server creates the in-memory scoreboard owned by the user and group ID of the parent Apache process, which is more secure. In the rare case that the old behavior of creating the scoreboard with the user and group defined by the User and Group directives (which is technically wrong) specify the directive ScmemUIDisUser on; the default is off. In other words, unless you know you need to use this directive, you almost certainly donít.

The CoreDumpDirectory directive determines where Apache will attempt to dump core in theóI hope rareóevent of a crash. By default, Apache uses the server root, but because under normal circumstances Apache should be running as a user that doesnít have the privilege to write to the server root, no file will be created. To get a core file for debugging purposes, the CoreDumpDirectory can be used to stipulate a different, writable directory, for example:

CoreDumpDirectory /home/highprogrammer/friendcomputer

Note that this is genuinely useful because Apache comes with source code, so debugging is actually possible. Building Apache from source makes this much more useful because the debugger will have something to get its teeth into. Itís important to note, however, that leaving this option set in a production server can lead to certain security risks associated with Denial of Service attacks if a flaw is found in the Apache server that can remotely crash the Apache server. This option should be left off in production environments. 

This chapter is from Pro Apache by Peter Wainwright. (Apress, 2004, ISBN: 1590593006). Check it out at your favorite bookstore today. Buy this book now.

 



 
 
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