New Zealand Linux

Do your usual install on wordpress, and get it up and running. If you are not sure what that is, download the zip, upload the contents to your website, then point your browser at it to finish the configuration.
Once you have filled out your database information, and sorted themes etc you can then move onto the next step. Do not enable any plugins at this stage, some may be incompatible with multiuser!

Look for the file wp-config.php on your server, you need to edit it and add in one line to it.

define('WP_ALLOW_MULTISITE', true);

Once you have added it, refresh your dashboard and go to Network settings under Tools section. This will give you two Options
* Subdirectories as in http://yourdomain.com/someuser/
* Subdomains as in http://user.yourdomain.com

Most people will want to use subdomains, This will require a wildcard DNS entry however. That means just add an A record of * pointing to the IP of your server, then add in the apache config below before restarting.

ServerAlias *.yourdomain.com

Once you have done this you can go under the SuperUser menu and add a site in.

Some extra wordpress notes:
* make the plugins/themes folder writable by the web server. It needs to be owned by the same user not just chmod 777/666 for some reason on a lot/most systems. This is so it can read/write plugins etc without the FTP details. Using the FTP is a more secure option, however it can be painful and annoying to do.
* Not all plugins are compatible with multiuser
* Security can be a problem, one site gets compromised, all sites may be.

libapache2-mod-bw – bandwidth limiting module

This module allows you to limit bandwidth usage on every virtual host or directory or to restrict the number of simultaneous connections.

The bandwidth control, for example, can be configured according to the criteria: origin of the connection, file extension, file size or user agent of the client.
Example:

LoadModule bw_module /usr/lib/apache2/modules/mod_bw.so
BandWidthModule On
BandWidth all 40000
MinBandWidth all 10000
ForceBandWidthModule On

libapache2-mod-defensible – module for Apache2 which provides DNSBL usage

mod_defensible implements usage of DNSBL servers to block access to a Web site or to specific locations.

Example:

DnsblUse On
DnsblServers httpbl.abuse.ch sbl-xbl.spamhaus.org
DnsblNameserver 145.253.2.75

libapache2-mod-evasive – evasive module to minimize HTTP DoS or brute force attacks

mod_evasive is an evasive maneuvers module for Apache to provide some protection in the event of an HTTP DoS or DDoS attack or brute force attack.

It is also designed to be a detection tool, and can be easily configured to talk to ipchains, firewalls, routers, and etcetera.

Example:

<IfModule mod_evasive20.c>
DOSHashTableSize 3097
DOSPageCount 5
DOSSiteCount 100
DOSPageInterval 1
DOSSiteInterval 1
DOSBlockingPeriod 600
</IfModule>

Comes with a perl script to test it also.

vps:/etc/apache2/mods-available# perl /usr/share/doc/libapache2-mod-evasive/examples/test.pl
HTTP/1.1 200 OK
HTTP/1.1 200 OK
HTTP/1.1 200 OK
HTTP/1.1 200 OK
HTTP/1.1 200 OK
HTTP/1.1 200 OK
HTTP/1.1 403 Forbidden
HTTP/1.1 403 Forbidden
HTTP/1.1 403 Forbidden
HTTP/1.1 403 Forbidden

libapache2-mod-line-edit – search-and-replace line editor module for apache 2

mod_line_edit is a general-purpose apache 2 filter for text documents. It operates as a simple on-the-fly line editor, applying search-and-replace rules defined in a configuration or .htaccess file. Both simple text and regular expression search and replace are supported.

Example:

SetOutputFilter line-editor
SetEnv LineEdit “text/plain;text/css;text/html”
LELineEnd ANY
LERewriteRule https?://(www\.)?example\.com http://example-development.yoursite.co.nz Ri

Throw something like that into your or somewhere and you instantly fixed all those problem URLS on your development system, without touching the source files at all.
This is ideal to stop/prevent people exploiting various holes in web applications and inserting javascript redirects etc.

Please note: the name of all these modules is debian/ubuntu related. Centos or RedHat based distros may have another name for the same modules. If you need any of these installed just drop an email into the support box and let us know.

A lot of people use postfixadmin, it means email users are in the database, its easy to use, easy to admin. However the setup can be a little tricky for those not used to it.

If you want to have a go doing it yourself, there is a great tutorial here http://rimuhosting.com/knowledgebase/linux/mail/postfixadmin

Today however we had the most exasperating problem trying to get postfix to connect to the database however on one particular VPS. 2 of us sat for over an hour trying to figure out why all the credentials worked fine, but postfix still couldnt connect.

The logs had the following error messages

Nov 5 01:12:40 hostname postfix/trivial-rewrite[8740]: warning: connect to mysql server localhost: Can’t connect to local MySQL server through socket ‘/var/run/mysqld/mysqld.sock’ (40)
Nov 5 01:12:40 hostname postfix/trivial-rewrite[8740]: fatal: mysql:/etc/postfix/mysql_virtual_alias_maps.cf(0,lock|fold_fix): table lookup problem
Nov 5 01:12:40 hostname postfix/trivial-rewrite[8741]: warning: connect to mysql server localhost: Can’t connect to local MySQL server through socket ‘/var/run/mysqld/mysqld.sock’ (40)
Nov 5 01:12:40 hostname postfix/trivial-rewrite[8741]: fatal: mysql:/etc/postfix/mysql_virtual_alias_maps.cf(0,lock|fold_fix): table lookup problem
Nov 5 01:12:41 hostname postfix/smtpd[8657]: warning: problem talking to service rewrite: Success
Nov 5 01:12:41 hostname postfix/smtpd[8491]: warning: problem talking to service rewrite: Connection reset by peer
Nov 5 01:12:41 hostname postfix/master[8481]: warning: process /usr/lib/postfix/trivial-rewrite pid 8740 exit status 1
Nov 5 01:12:41 hostname postfix/master[8481]: warning: /usr/lib/postfix/trivial-rewrite: bad command startup — throttling
Nov 5 01:12:41 hostname postfix/smtpd[8685]: warning: problem talking to service rewrite: Success
Nov 5 01:12:41 hostname postfix/master[8481]: warning: process /usr/lib/postfix/trivial-rewrite pid 8741 exit status 1

So clearly it was a case of not being able to connect to the MySQL server, but why? the user was fine, the host was fine, everything was checked, and rechecked. Finally I saw an email which touched on postfix being in a chroot, which meant it was unable to access the mysql.sock file (i had already checked permissions on this multiple times by now).

To make a long story short, this is a Debian based box, and the fix is to change the mysql socket to a place that the mail could access it.

/etc/init.d/mysql stop
cd /etc/mysql
mkdir backup # always
cp *.cnf backup/ # backup everything
sed -i s@/var/run/mysqld/@/var/spool/postfix/var/run/mysqld/@g my.cnf # this edits the file inline
sed -i s@/var/run/mysqld/@/var/spool/postfix/var/run/mysqld/@g debian.cnf #changing the socket location
mkdir /var/spool/postfix/var/run/mysqld/
chown mysql /var/spool/postfix/var/run/mysqld/
/etc/init.d/mysql start

This changed the mysql sock into a directory so that they postfix was able to access it, enabling all mail to run freely.