Issue

Networks eth0, eth1 and eth2 doesn't start automatically.

Investigation done

Found the following root causes for this issue:

1. On Boot was set to 'No' in eth0, eth1 and eth2 

2. eth0, eth1 and eth2 nicknames were given as eth0.bak, eth1.bak and eth2.bak respectively

3. Network Manager service was not running

Resolution

A. Set On Boot to Yes in eth0, eth1 and eth2 corresponding files. This will make sure that the network starts automatically on booting the system.

1. Open /etc/sysconfig/network-scripts/ifcfg-eth0 file and set ON BOOT to yes:

[root@idm117 ~]# cat /etc/sysconfig/network-scripts/ifcfg-eth0
# Realtek Semiconductor Co., Ltd. RTL-8139/8139C/8139C+
DEVICE=eth0
BOOTPROTO=dhcp
ONBOOT=yes
HWADDR=00:21:f6:00:00:3a
TYPE=Ethernet
USERCTL=no
IPV6INIT=no
PEERDNS=yes

2. Do the same for eth1 and eth2 respectively.

B. Rename eth0, eth1 and eth2 nicknames.

3. In my case eth0 nickname was set to eth0.bak. So I simply renamed it to eth0.

cd /etc/sysconfig/network-scripts

mv ifcfg-eth0.bak ifcfg-eth0

4. Do the same for eth1 and eth2 respectively.

C. Make sure Network Manager service is running

5. Issue the following command to check the status of Network Manager service

service NetworkManager status

6. If its not running then issue the following command to start it:

service NetworkManager start

7. Make sure Network Manager also gets started automatically on boot:

chkconfig NetworkManager on

8. Now simply reboot the system and you will see that the networks eth0, eth1 and eth2 starts up automatically on boot.

Environment

+ Oracle Linux 5.7