How to mount LVM partitions from rescue mode (Fedora/CentOS/RedHat)

Boot your rescue media.
Scan for volume groups:
# lvm vgscan -v
Activate all volume groups:
# lvm vgchange -a y
List logical volumes:
# lvm lvs –all
With this information, and the volumes activated, you should be able to mount the volumes:
# mount /dev/volumegroup/logicalvolume /mountpoint

How to convert RHEL5 to CentOS5

# Determine version and architecture of installed RHEL
cat /etc/redhat-release
uname -i

# Go to working directory
mkdir /root/centos5
cd /root/centos5
# Download the necessary files
wget http://mirror.umd.edu/centos/5.8/os/x86_64/CentOS/centos-release-notes-5.8-0.x86_64.rpm
wget http://mirror.umd.edu/centos/5.8/os/x86_64/CentOS/centos-release-5-8.el5.centos.x86_64.rpm
wget http://mirror.umd.edu/centos/5.8/os/x86_64/CentOS/yum-3.2.22-39.el5.centos.noarch.rpm
wget http://mirror.umd.edu/centos/5.8/os/x86_64/CentOS/yum-fastestmirror-1.1.16-21.el5.centos.noarch.rpm
wget http://mirror.umd.edu/centos/5.8/os/x86_64/CentOS/yum-utils-1.1.16-21.el5.centos.noarch.rpm
wget http://mirror.umd.edu/centos/5.8/os/x86_64/RPM-GPG-KEY-CentOS-5

# Import the rpm gpg signing key
rpm --import RPM-GPG-KEY-CentOS-5

# Remove the following packages
rpm -e --nodeps redhat-release-5Server
rpm -e yum-rhn-plugin rhn-check rhnsd rhn-setup rhn-client-tools rhncfg rhncfg-client rhncfg-actions subscription-manager

# Force install the five rpm files in the working directory
rpm -Uvh --force *.rpm

# Yum update the system
yum update

# Reboot
shutdown -r now

# To avoid confusion later
sed -i 's/Red Hat Enterprise Linux Server/CentOS Server/g' /boot/grub/grub.conf

How to convert RHEL6 to CentOS6

# Remove all the yum metadata from the system
yum clean all

# Make a working directory and go there
mkdir /root/centos
cd /root/centos/

# Check the version and architecture of RHEL 
# currently installed
cat /etc/redhat-release
uname -i

# Download the following 4 RPM files and 1 RPM-GPG-KEY file
# from http://mirror.umd.edu/centos/{VER}/os/{ARCH}/
# In this example, we are converting RHEL 6.1 x86_64. We will 
# use the latest available version of the following packages.

wget http://mirror.umd.edu/centos/6.2/os/x86_64/Packages/centos-release-6-2.el6.centos.7.x86_64.rpm
wget http://mirror.umd.edu/centos/6.2/os/x86_64/Packages/yum-3.2.29-22.el6.centos.noarch.rpm
wget http://mirror.umd.edu/centos/6.2/os/x86_64/Packages/yum-utils-1.1.30-10.el6.noarch.rpm
wget http://mirror.umd.edu/centos/6.2/os/x86_64/Packages/yum-plugin-fastestmirror-1.1.30-10.el6.noarch.rpm
wget http://mirror.umd.edu/centos/6.2/os/x86_64/RPM-GPG-KEY-CentOS-6

# Import the GPG signing key
rpm --import RPM-GPG-KEY-CentOS-6

# Remove the following RPMS from the system
rpm -e --nodeps redhat-release-server
rpm -e yum-rhn-plugin rhn-check rhnsd rhn-setup rhn-setup-gnome
# If the second rpm command fails because a package is not installed, 
# remove the name of that package from
# the command line and re-run the command.

# Force install all 4 RPMS in the working directory
rpm -Uvh --force *.rpm

# Do a yum upgrade. It should go to a CentOS download site and ask 
# to upgrade a lot of packages
yum upgrade

# Reboot the system
shutdown -r now