Ubuntu Server 13.10 now goes to sleep when closing laptop lid
http://askubuntu.com/questions/360615/ubuntu-server-13-10-now-goes-to-sleep-when-closing-laptop-lid

To disable entering the sleep mode edit the /etc/systemd/logind.conf file and uncomment/modify/add the line:
HandleLidSwitch=ignore
Then execute sudo restart systemd-logind or simply reboot.

Keep Ubuntu Server running on a laptop with the lid closed?
http://askubuntu.com/questions/141866/keep-ubuntu-server-running-on-a-laptop-with-the-lid-closed

apt-get install acpi-support

Edit /etc/acpi/event/lidbtn and comment out the bottom two lines:
  event=button[ /]lid  # comment this out with a # at the beginning
  action=/etc/acpi/lid.sh # same here
Reboot, and that should be it.