Read more on Apache Software Foundation Blog.

But there two big disadvantages using this method:

1. If your config is invalid, Apache will shutdown and not start again
2. Users currently accessing your server will recognize that Apache will not answer request for a short time

Indeed there is a much more better method to restart the Apache “gracefully”:

apache2ctl -t
Syntax OK

apache2ctl -k graceful

The first command will tell Apache to check your config. If everything is correct, you will get “Syntax OK”, otherwise the error will be reported but Apache will still run with the old configuration.

The second command will tell Apache to restart gracefully with the advantage that currently open connections are not aborted and the users will not be annoyed.

There are two reasons to redirect e.g. mydomain1.de to www.mydomain1.de:

1. It avoids detecting search machines “double content”
2. I personally prefer having one unique URL for a homepage, also if a user enters mydomain1.de he will be redirected to www.mydomain1.de

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^mydomain\.de$ [NC]
RewriteRule ^(.*) http://www.mydomain.de/$1 [L,R=301]

The redirect is defined as 301 “permanent”. Please note that these rewrite settings only work if the correct setting for “AllowOverride” is done within the Apache settings of your host or virtual host configuration.

Redirect Domain to another Domain

If you want to redirect a complete domain, here mydomain1.de including subdomains to another domain e.g. mydomain2.de put the following code into the .htaccess of the web root directory of mydomain1.de:

RewriteEngine On
RewriteBase /
RewriteCond %{HTTP_HOST} ^(.*)mydomain1\.de$
RewriteRule ^(.*)$ http://www.mydomain2.de/$1 [R=301,L,NC]

Using this rewrite condition all hosts *.mydomain1.de including mydomain1.de will be redirected to www.mydomain2.de. Everything behind .de/ will be kept.

Furthermore the redirect is defined as 301 which means permanent redirect. This will avoid that search machines like Goole will treat you with “double content”.

Hint

Be sure you have enabled “Options FollowSymLinks” or Options “SymLinksIfOwnerMatch” in your Apache or virtual host config. Otherwise mod rewrite will not work!

Working with Apache/2.2.3

Timeout 30
KeepAlive On
MaxKeepAliveRequests 100
KeepAliveTimeout 5
<IfModule mpm_prefork_module>
StartServers         16
ServerLimit         512
MinSpareServers      16
MaxSpareServers      128
MaxClients          256
MaxRequestsPerChild 55555
</IfModule>
HostnameLookups Off
ServerTokens Prodme
ServerSignature Off
UseCanonicalName Off
TraceEnable Off

HostNameLookups Off are recommended in any case.

You can check the opened log file from apache using the command:

lsof |grep apache|grep log

Oh yes, if you serve lot’s of domains on your server this list will be quite long. To disable logging just uncomment the corresponding lines e.g. in your virtual host definition:

#ErrorLog /var/log/apachd2/mydonain.de-error_log
#CustomLog /var/log/apache2/mydomain.de-access_log combined

Afterwards check your apace configuration for errors:

apache2ctl -t

In case of syntax OK just restart your apache server:

apache2ctl -k graceful

This command is qute because it does a “graceful” restart without anoying users accesing your server right now.

Hint

How to check if my disc IO is high?

Use the command “vmstat 1″ and check the section “IO” (what else…). You will see bi and bo which means blocks received and blocks sent. In case the numbers are high, you will have high disc IO.

procs -----------memory---------- ---swap-- -----io---- -system-- ----cpu----
r  b   swpd   free   buff  cache   si   so    bi    bo   in   cs us sy id wa
0  0 659476  41604   8732 347304    3    3    37    41   20   14 19  7 58 16
3  0 659476  41604   8732 347336    0    0     0     0  410  314  7  0 93  0
0  0 659476  41464   8740 347328    0    0     0   424  522  321 11  1 86  2

Apache needs a lot of memory, this will decrease performance on a machine with e.g. 1 GByte memory and about 60 users accessing the server simultaneously a lot. There is a simply method to save memory: disable all unused modules. Yes, it really helps!

Why does it help? Because every apache process started – and a lot will be started when several users are accessing the server – will load all enabled modules.

To get an overview how much memory is consumed by the modules use the command

lsof | grep apache | grep modules

Using this command you will also see which modules consumes much memory.

In my case only the following modules are used:

• actions.load
• authz_default.load
• authn_file.load
• auth_basic.load
• authz_user.load
• env.load
• mime.load
• rewrite.load
• userdir.load
• alias.load
• authz_host.load
• deflate.load
• expires.load
• negotiation.load
• setenvif.load
• headers.load
• speling.load
• cgi.load
• dir.load
• include.load
• php5.load

Modules which are not needed are disabled using the command

a2dismod <module_name>