This install procedure can be used in a generic OpenVZ or Virtuozzo environment or inside an all in one OpenVZ installer+GUI product such as Proxmox VE.  I am not sure how relevant it would be for Xen.  This guide covers the installation INSIDE an already created OpenVZ/Virtuozzo container (VPS sans Operating System) which would then become a functioning Virtual Private Server (VPS).  I will not be covering the OpenVZ host setup or iptables or zaptel/dahdi setup inside or outside the OpenVZ environment.

Software used:

CentOS 5-x86_64 OpenVZ template
Asterisk 1.6
FreePBX 2.6

Linux commands executed at a command prompt are in courier font.
Output as a result of linux commands are in Verdana font.

64 or 32bit
It is common to run OpenVZ/Virtuozzo setups with 64bit host OS and 32bit VPS's due to lower memory usage within VPS containers combined with the larger memory addressability of the 64bit Host.  If you run Asterisk/FreePBX in a 32bit VPS on a 64bit host you won't have MeetMe conferencing because Zaptel/Dahdi needs to be installed on the host and will not work in a mixed environment the way it is written now.  The options are to run both host and VPS on 32bit or 64bit.  Running a 64bit Asterisk/Freepbx VPS requires a bit more more memory (perhaps 20-60MB more) which can be a factor in a shared memory VPS environment.

Why OpenVZ
For those not familiar with OpenVZ/Virtuozzo terminology, a container is the Virtual Private Server (VPS) shell into which is installed a pre-created operating system (template).  This can be any operating system that uses the common Linux Kernel such as Redhat, CentOS, Ubuntu, Gentoo, Debian, SuSE etc.  You can create them yourself on a host system or use pre-created ones available on the OpenVZ website.  The main restriction is that all versions are running on the same kernel.  The advantage is that the kernel only needs to be updated once on the host in order to update all the VPS's.  Besides all that, before jumping into this stuff I looked into the alternatives such as Xen and KVM over IP and I believe OpenVZ offers the best performing platform for running Asterisk on a VPS.

Let's get started
Once the OpenVZ/Virtuozzo container is created install the CentOS 5-x86_64 template into the container.  Log into the VPS as root with an SSH client such as PuTTy.  Another handy tool is WinSCP for browsing directories and editing files in a more intuitive Graphical environment.

If using 64bit get rid of all 32bit packages in the 64bit VPS.  They are not necessary and may cause hard to find conflicts.

yum remove *.i?86

Clean out yum to ensure all cached packages and mirrored server references are removed.
yum clean all

Get rid of all installed groups except 'Yum Utilities' so we are starting with a clean slate.  Check the delete list before entering 'y' to make sure none of these remove 'sshd' or 'yum' (they don't but check just in case things change with newer revisions).

yum grouplist installed

Installed Groups:
   DNS Name Server
   Editors
   Legacy Network Server
   Mail Server
   Network Servers
   System Tools
   Text-based Internet
   Web Server
   Windows File Server
   Yum Utilities

yum groupremove 'DNS Name Server'
yum groupremove 'Editors'
yum groupremove 'Legacy Network Server'
yum groupremove 'Mail Server'
yum groupremove 'Network Servers'
yum groupremove 'System Tools'
yum groupremove 'Text-based Internet'
yum groupremove 'Web Server'
yum groupremove 'Windows File Server'

If installing 64bit VPS edit yum.conf to prevent 32bit packages from being installed.  If that happens it may have unintended consequences.
yum install -y nano
nano /etc/yum.conf

Add the following line.
exclude=*.i?86

(Ctrl-x> y >Enter)

 
Now update the base install
yum -y update

Install Asterisk/FreePBX required packages, other useful packages, and their dependencies

yum groupinstall core
yum groupinstall base

yum install gcc gcc-c++ wget bison mysql-devel mysql-server php php-mysql php-pear php-pear-DB php-mbstring nano tftp-server httpd make ncurses-devel libtermcap-devel sendmail sendmail-cf caching-nameserver sox newt-devel libxml2-devel libtiff-devel php-gd audiofile-devel gtk2-devel

Get rid of some unnecessary packages.  I have no doubt there are many other packages that could be added to this list.  These are the ones I found that are resident in memory by default.  Since memory is at a premium on a VPS, removing these will help reduce the memory footprint.
yum remove yum-updatesd cups cups-lpd redhat-lsb autofs pcsc-lite smartmontools cpuspeed avahi

To prevent common udev problems in OpenVZ VPS do the following:

nano /etc/rc.local

add the following lines:

/bin/rm -rf /dev/null
/bin/rm -rf /dev/random
/bin/rm -rf /dev/tty*
/bin/rm -rf /dev/pty*
/bin/mknod /dev/null c 1 3
/bin/mknod /dev/random c 1 8
/sbin/MAKEDEV tty
/sbin/MAKEDEV pty

(Ctrl-x> y >Enter)

Selinux is not compatible with OpenVZ. Create the following file and copy paste the contents indicated here just to be sure selinux never runs.

nano /etc/selinux/config

# This file controls the state of SELinux on the system.
# SELINUX= can take one of these three values:
#       enforcing - SELinux security policy is enforced.
#       permissive - SELinux prints warnings instead of enforcing.
#       disabled - SELinux is fully disabled.
SELINUX=disabled
# SELINUXTYPE= type of policy in use. Possible values are:
#       targeted - Only targeted network daemons are protected.
#       strict - Full SELinux protection.
SELINUXTYPE=targeted
# SETLOCALDEFS= Check local definition changes
SETLOCALDEFS=0

(Ctrl-x> y >Enter)

Make sure selinux is turned off for this session
setenforce 0

Enable the tftp server on startup if required (for configuring phones on LAN or VPN)
nano /etc/xinetd.d/tftp
change “disable=yes” to “disable=no”
(Ctrl-X>y>ENTER)

 

Set timezone: 
Create a symbolic link to the appropriate timezone from /etc/localtime.
Example:ln -sf /usr/share/zoneinfo/America/Vancouver /etc/localtime

Download and untar source files.  Since this is a shared kernel environment we cannot make use of zaptel/dahdi hardware in the physical server and cannot install the zaptel/dahdi kernel module inside the virtual servers.  The zaptel/dahdi kernel module must be installed on the host server kernel with some special configurations and sharing of files for each virtual server. This is only required for enabling meetme conferencing during Asterisk installation as of Asterisk 1.6.1 and will not be required at all eventually.  This is all beyond the scope of this document.  If you require meetme conferencing and have access to the host operating system you can complete this procedure in the VPS first and then return after zaptel/dahdi is installed on the host system and re-compile Asterisk with meetme conferencing enabled.

Install lame mp3 encoder (not recommended) if you plan to make use of mp3's for MOH.  This is now a legacy feature as the default behaviour of Asterisk/Freepbx is to NOT use mp3's for anything.  Freepbx by default now automatically converts uploaded mp3's to wav.
rpm -ivh http://apt.sw.be/redhat/el5/en/x86_64/RPMS.dag/lame-3.98.2-1.el5.rf.x86_64.rpm

Get FreePBX.  Check if this is the latest released version.
cd /usr/src
wget http://mirror.freepbx.org/freepbx-2.6.0RC2.tar.gz
tar zxvf freepbx-2.6.0RC2.tar.gz

Get Asterisk and addons.  Check if this is the latest released version of Asterisk and Asterisk addons
wget http://downloads.asterisk.org/pub/telephony/asterisk/releases/asterisk-1.6.0.17.tar.gz
tar zxvf asterisk-1.6.0.17.tar.gz

wget http://downloads.asterisk.org/pub/telephony/asterisk/releases/asterisk-addons-1.6.0.3.tar.gz
tar zxvf asterisk-addons-1.6.0.3.tar.gz

Configure and compile Asterisk
cd /usr/src/asterisk-1.6.0.17
make clean
./configure; make menuselect
select the core sounds you want.  Same with addon sounds.  I suggest ulaw as they sound better than gsm.
At menu press "x" to save

make
make install

Do NOT run "make samples".  I have found it causes problems down the line with FreePBX.  Not insurmountable but just more things to have to deal with that you probably don't want to.

Create users and set permissions
useradd -c "Asterisk PBX" -d /var/lib/asterisk asterisk

mkdir /var/run/asterisk
chown -R asterisk /var/run/asterisk
chown -R asterisk /var/log/asterisk
chown -R asterisk /var/lib/asterisk/moh
chown -R asterisk /var/lib/php/session

Music on Hold
Since the Asterisk default moh directory (/moh) and the Freepbx default moh directory (/mohmp3) are different we need to create a symbolic link so moh files are where FreePBX expect them to be.
ln -s /var/lib/asterisk/moh /var/lib/asterisk/mohmp3

The new default behaviour for Asterisk and Freepbx is to only use wav files for moh due to transcoding overhead and Asterisk stability issues with mp3's. So we want to install mpg123 for converting uploaded mp3's to wav automagically.  If you won't be uploading or streaming mp3's or won't be using FreePBX (new) default behaviour then you probably don't need to install mpg123.

cd /usr/src
wget http://sourceforge.net/projects/mpg123/files/mpg123/1.9.1/mpg123-1.9.1.tar.bz2/download
tar -xjvf mpg123-1.9.1.tar.bz2

cd mpg123-1.9.1
make clean
./configure
make
make install

Freepbx php script cannot find mpg123 by default so we need to create a symbolic link.
ln -s /usr/local/bin/mpg123 /usr/bin/mpg123

Change User apache and Group apache to User asterisk and Group asterisk.

sed -i "s/User apache/User asterisk/" /etc/httpd/conf/httpd.conf
sed -i "s/Group apache/Group asterisk/" /etc/httpd/conf/httpd.conf

You can choose to change the default AllowOverride All to AllowOverride None to prevent .htaccess permission problems which can be frustrating to troubleshoot.
sed -i "s/AllowOverride All/AllowOverride None/" /etc/httpd/conf/httpd.conf

Before you can do anything to MySQL, you need to make sure it's running:

/etc/init.d/mysqld start
Initializing MySQL database:                               [  OK  ]
Starting MySQL:                                            [  OK  ]

Now, to configure the databases for freePBX:
Note: If mysql admin password is already configured, add "-p" after the command and enter password when asked.  For example, "mysqladmin -p create asterisk"

cd /usr/src/freepbx-2.6.0RC2
mysqladmin create asterisk
mysqladmin create asteriskcdrdb
mysql asterisk < SQL/newinstall.sql
mysql asteriskcdrdb < SQL/cdr_mysql_table.sql

They also need to be secured.  FreePBX will prompt you for a database username/password when you do the install. You need to pick that now. We'll assume that you've picked 'asteriskuser' and 'amp109' - you probably shouldn't use these, as they are well known passwords for Freepbx.  MySQL only listens to localhost by default so I would not get too paranoid about using these defaults.

mysql
Welcome to the MySQL monitor.  Commands end with ; or \g.
Your MySQL connection id is 8 to server version: 4.1.16

Type 'help;' or '\h' for help. Type '\c' to clear the buffer.

mysql> GRANT ALL PRIVILEGES ON asteriskcdrdb.* TO asteriskuser@localhost IDENTIFIED BY 'amp109';
Query OK, 0 rows affected (0.00 sec)

mysql> GRANT ALL PRIVILEGES ON asterisk.* TO asteriskuser@localhost IDENTIFIED BY 'amp109';
Query OK, 0 rows affected (0.00 sec)

mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)

mysql> \q
Bye

Now, after all of this, you need to pick a root 'mysql' password. We'll make it 'abcdef' just for this example.  You should use a reasonably strong password. If you need to do anything else with mysql, you'll need to provide this password.
mysqladmin -u root password 'abcdef'

Build the cdr_mysql module for Asterisk
cd /usr/src/asterisk-addons-1.6.0.3

make clean
./configure; make menuselect

You can check options but should leave all at default selections.  At menu press "x"

make; make install

edit /usr/sbin/safe_asterisk and comment out TTY=9 to prevent errors in OpenVZ VPS
nano +5 /usr/sbin/safe_asterisk
#TTY=9

Prioritize Asterisk Process
Increase Asterisk process priority.  You can experiment with different values and see what works best.  I wouldn't go too high as it could cause other problems.  From the command 'top' the PR column shows absolute priority and NI column is the relative number we add here.  Default is 0 which gives Asterisk about the same default priority as httpd and mysql.  5-10 should give top priority without crippling critical background tasks.  I believe you can go as high as 20.  This is only a prioritization recommendation setting.  The process scheduler still has ultimate authority so actual priority will vary from system to system depending on what else is installed.
nano +22 /usr/sbin/safe_asterisk
PRIORITY=10

(Ctl-x > y >ENTER)

Install FreePBX

/usr/sbin/safe_asterisk
If you didn't 'run make samples' when you installed asterisk you will probably get some warning messages saying no modules will be loaded.  Just ignore and press 'ENTER' to get a command prompt.

cd /usr/src/freepbx-2.6.0RC2
./install_amp

If you get any warnings or errors in the last part of the output, they're usually not traumatic.
Leave AMPWEBADDRESS=xx.xx.xx.xx blank

nano /etc/amportal.conf
AMPWEBADDRESS=

To enable password protection of the Web GUI set:
AUTHTYPE=database

Default username is: admin
Default pw is: admin

Edit /etc/asterisk/cdr_mysql.conf and add 'loguniqueid=yes' to the global section

nano /etc/asterisk/cdr_mysql.conf
loguniqueid=yes

set FreePBX to start on boot
echo /usr/local/sbin/amportal start >> /etc/rc.local

Enable Apache and mysql to start on boot
chkconfig httpd on
chkconfig mysqld on
Now reboot at which point you should be able to access freePBX with your web browser.  The very first thing you need to do when you enter the FreePBX Admin GUI for the first time is "Apply Configuration Changes" so all the *.conf files are created then reboot again or 'amportal restart' from command prompt.

To change the password for administrator "recordings" GUI (access to extension voicemail, call monitoring, recording etc.)
nano +73 /var/www/html/recordings/includes/main.conf.php

$ARI_ADMIN_PASSWORD ="password"

change the “max filesize” from 2M to 20M to allow larger music on hold files
nano +582 /etc/php.ini

Edit Apache web server for GUI access using a port other than 80 (optional):
nano /etc/httpd/conf/httpd.conf
change "Listen 80" to "Listen 8888" or whatever port you want

/etc/rc.d/init.d/httpd restart

Instead of accessing FreePBX by http://xxx.xxx.xxx.xxx
You now access it by http://xxx.xxx.xxx.xxx:8888

Edit /etc/aliases file  and add a “root: username_to_forward_to” to forward all ‘root’ messages to your personal email address.  Put in the full email address if it is not on the asterisk system itself.
Then run  
/usr/bin/newaliases
to restart the service.

NOTE: If you are installing on a LAN or do not have a domain resolving to the IP of the VPS, Sendmail will hang for a couple minutes everytime you reboot.  To prevent this your VPS hostname should end with .local or .localhost.  So, for example, instead of naming the VPS hostname 'powerpbx' it should be named 'powerpbx.local'.  The manual method is to edit your /etc/hosts file.  There should be 2 lines.
127.0.0.1 localhost.localdomain localhost
yourIPaddress yourhostname.local yourhostname yourhostname

MySQL performance tuning for low memory
This will reduce memory usage significantly without affecting performance.

nano /etc/my.cnf
[mysqld]
.
.
.
skip-innodb
skip-bdb

(Ctl-x > y > ENTER)

From command prompt:
service mysqld restart

Bit of housekeeping
Asterisk installs *.sln sound files to the moh directory.  FreePBX does not see *.sln files (yet) so they will not show up in the FreePBX moh GUI even though they will still play when people are put on hold.  It's best to just delete these files to avoid confusion.  Also, there is a bug in asterisk 1.6.1.x where MOH tries to play some text files in that directory that are just license information etc..  The result is MOH will intermittently stop working.  If you are still running 1.6.1.x delete these text files as well.

rm /var/lib/asterisk/moh/*.sln