Browsing the blog archives for January, 2016.

Error Restarting Network Service in CentOS 7


Today I got this error message when restarting network service with # systemctl restart network.service or # service network restart:

Restarting network (via systemctl): Job for network.service failed. See 'systemctl status network.service' and 'journalctl -xn' for details.

Browsing around for a while, then found this solution:

# systemctl stop NetworkManager
# systemctl disable NetworkManager

After disabling NetworkManger, restarting network service succeeded.


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All-in-One Software Defined Network (SDN) VM


If you want to jumpstart learning SDN without installing every single software on operating system, Srini Seetharaman has all-in-one VM that already installed with necessary SDN learning software.

The sofware and tools installed on the VM (listed by

  • SDN Controllers: OpenDaylight, ONOS, RYU, Floodlight, Floodlight-OF1.3, POX, and Trema
  • Example code for a hub, L2 learning switch, traffic tap, and other applications
  • Open vSwitch 2.3.0 with support for Openflow 1.2, 1.3 and 1.4, and LINC switch
  • Mininet to create and run example topologies
  • Pyretic
  • Wireshark 1.12.1 with native support for OpenFlow parsing
  • JDK 1.8, Eclipse Luna, and Maven 3.3.3

These are the instruction steps:

  1. Install VirtualBox or Vmware Player/Fusion
  2. Install Putty and Xming (for Windows) or Xquartz (for Mac)
  3. Download appliance from one of these link:
  4. Import downloaded file (SDN_tutorial_VM_XXbit.ova) to VirtualBox or Vmware Player/Fusion
  5. Start the VM (user/password: ubuntu/ubuntu)


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