How to Generalize a Linux VM Template

When building out an environment of any kind, you need to have a good starting base, a strong foundation and the same holds true for many things. It’s no different when building a virtual machine (VM) template to deploy in your environment in a repeatable fashion.

Recently I spent some time developing a generalized/sanitized VM template for Red Hat Enterprise Linux (RHEL) versions 6 and 7. This script should be run right before you shutdown the VM and template it for reuse.

#!/bin/bash
echo "Generalize the template..."
echo "Remove RHN system ID..."
rm -f /etc/sysconfig/rhn/systemid

echo "Create sanitized ifcfg-eth0..."
echo -en 'DEVICE=eth0\nTYPE=Ethernet\nONBOOT=yes\nBOOTPROTO=dhcp\n' > /etc/sysconfig/network-scripts/ifcfg-eth0

echo "Clear /etc/sysconfig/network file..."
cat > /etc/sysconfig/network < /dev/null

echo "Remove SHH keys..."
rm -f /etc/ssh/ssh_host_*

echo "Remove udev rules..."
rm -f /etc/udev/rules.d/70-*

echo "Remove fixed hostname..."
rm -f /etc/hostname

echo "Clear Machine ID (SID)..."
> /etc/machine-id

echo "Remove all logs from /var/log..."
rm -rf /var/log/*

echo "Remove all logs from /root..."
rm -rf /root/*