Prevent the incrementing of eth devices on Linux systems after guest customization of a cloned VM

After the guest customization process runs on cloned VMs in some VMware products, you may notice that on your Linux systems the eth device number gets incremented.  For example, when the system is first built, the first eth device will be eth0.  If the system is cloned & customized, the eth device will become eth1.  This may not be a problem on some systems, but people often need/prefer the first eth device to be eth0 or at least to not change after the system is customized.

The issue arises because of old entries in the udev network file – /etc/udev/rules.d/70-persistent-net.rules.  After an initial install of a Linux system that has a NIC with a MAC of “00:50:56:02:00:7c”, /etc/udev/rules.d/70-persistent-net.rules will look something like

# This file was automatically generated by the /lib/udev/write_net_rules
# program, run by the persistent-net-generator.rules rules file.
#
# You can modify it, as long as you keep each rule on a single
# line, and change only the value of the NAME= key.

# PCI device 0x15ad:0x07b0 (vmxnet3)
SUBSYSTEM==”net”, ACTION==”add”, DRIVERS==”?*”, ATTR{address}==”00:50:56:02:00:7c”, ATTR{type}==”1″, KERNEL==”eth*”, NAME=”eth0″

When you perform a clone & customization (as in creating a new vApp from a template in vCloud), the source VM is cloned and has NIC with a new MAC address.  When the cloned VMs boots, udev notices the new NIC and updates /etc/udev/rules.d/70-persistent-net.rules with the new NIC and gives it the name eth1.

# This file was automatically generated by the /lib/udev/write_net_rules
# program, run by the persistent-net-generator.rules rules file.
#
# You can modify it, as long as you keep each rule on a single
# line, and change only the value of the NAME= key.

# PCI device 0x15ad:0x07b0 (vmxnet3)
SUBSYSTEM==”net”, ACTION==”add”, DRIVERS==”?*”, ATTR{address}==”00:50:56:02:00:7c”, ATTR{type}==”1″, KERNEL==”eth*”, NAME=”eth0″

# PCI device 0x15ad:0x07b0 (vmxnet3)
SUBSYSTEM==”net”, ACTION==”add”, DRIVERS==”?*”, ATTR{address}==”00:50:56:02:01:9e”, ATTR{type}==”1″, KERNEL==”eth*”, NAME=”eth1″

A new file named /etc/sysconfig/network-scripts/ifcfg-eth1 will be created that points to the eth1 device

DEVICE=eth1
NETMASK=255.255.255.0
IPADDR=192.168.5.101
BOOTPROTO=static
ONBOOT=yes

Now when ifconfig is ran, you will see eth1 instead of eth0.

To prevent the issue from occurring, delete the /etc/udev/rules.d/70-persistent-net.rules file before shutting down the VM and turning it into a template.  This will cause a new /etc/udev/rules.d/70-persistent-net.rules to be created when the customizing VM boots up.  The new file will only contain the NICs on the system and they should be labelled as eth0, eth1, etc.

Another thing you may want do before shutting the VM down to be added as a template is modify /etc/sysconfig/network-scripts/ifcfg-eth0 so that ONBOOT is set to no (ONBOOT=no).  I’ve seen issues in vCloud where multiple vApp templates are being deploying onto the same network and the VMs have the same IP (that was initially on the VM before it was turned into a template).  Then the systems boot, ifup is ran, which runs arping.  I’ve seen arpping return an error in these situations, which causes VMware tools to not start.  This then causes guest customization to fail since VMware tools is relied up by guest customization.

 

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One Comment on “Prevent the incrementing of eth devices on Linux systems after guest customization of a cloned VM”

  1. […] I’ve ran into this issue before and found the following article written by Chris Greene from Orchestration.io. […]


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