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Fixing eth0 when Cloning CentOS

19 November 2013

Summary

CentOS ties your ethernet interfaces to their MAC addresses. This is problematic when using CentOS in a virtualized environment, because it ends up preserving old ethernet interfaces. Fortunately, there is a quick fix.

Symptom

ifconfig only shows eth1 - where is eth0?

$ ifconfig -a
eth1      Link encap:Ethernet  HWaddr 00:50:56:B0:54:7E
          BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:4 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:260 (260.0 b)  TX bytes:260 (260.0 b)

Fix

Remove the files that have eth0’s hardware address and UUID, and then reboot. If using templates, run this command, shut down, and then create the template before rebooting.

 rm /etc/udev/rules.d/70-persistent-net.rules
 rm /etc/sysconfig/network-scripts/ifcfg-eth0
 reboot

Alternatively, edit ifcfg-eth0 and remove the lines with MAC and UUID.

Result

ifconfig should now show eth0.

$ ifconfig -a
eth0      Link encap:Ethernet  HWaddr 00:50:56:B0:54:7E
          BROADCAST MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:0 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:0 (0.0 b)  TX bytes:0 (0.0 b)

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          inet6 addr: ::1/128 Scope:Host
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:4 errors:0 dropped:0 overruns:0 frame:0
          TX packets:4 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:260 (260.0 b)  TX bytes:260 (260.0 b)