network is disabled

Question

I could successfully connect to network through livecd but through my hard disk it is not possible.

:~$ sudo ifup eth0
ifup: interface eth0 already configured

:~$ sudo lshw -class network
  *-network DISABLED      
       description: Ethernet interface
       product: RTL8101E/RTL8102E PCI Express Fast Ethernet controller
       vendor: Realtek Semiconductor Co., Ltd.
       physical id: 0
       bus info: pci@0000:02:00.0
       logical name: eth0
       version: 05
       serial: ff:ff:ff:ff:ff:ff
       size: 100Mbit/s
       capacity: 100Mbit/s
       width: 64 bits
       clock: 33MHz
       capabilities: pm msi pciexpress msix vpd bus_master cap_list ethernet physical tp mii 10bt 10bt-fd 100bt 100bt-fd autonegotiation
       configuration: autonegotiation=on broadcast=yes driver=r8169 driverversion=2.3LK-NAPI duplex=full latency=0 link=no multicast=yes port=MII speed=100Mbit/s
       resources: irq:40 ioport:e000(size=256) memory:f0004000-f0004fff memory:f0000000-f0003fff

:~$ sudo /etc/init.d/networking restart
 * Running /etc/init.d/networking restart is deprecated because it may not enable again some interfaces
 * Reconfiguring network interfaces...                                          RTNETLINK answers: No such process
SIOCSIFFLAGS: Cannot assign requested address
SIOCSIFFLAGS: Cannot assign requested address
RTNETLINK answers: Network is down
run-parts: /etc/network/if-up.d/avahi-autoipd exited with return code 2
                                                                         [ OK ]

Please let me know if you need more information.

Solution

I had a similar issue with a Realtek Ethernet controller. I had a different model, but it exhibited similar behavior to what you are describing. I was able to get it connected by running :

sudo ifconfig eth0 up

This command had to be run Everytime I started the computer, so you might find it beneficial to make the command a bash alias or shell script. If you need a guide for that, there are plenty to be found online.