Replace /etc/hostname entirely; clarify sources.list edit

util/vm/install-mininet-vm.sh

@@ -4,15 +4,17 @@
 # a brand-new Ubuntu virtual machine,
 # to create a fully usable "tutorial" VM.
 set -e
-echo `whoami` ALL=NOPASSWD: ALL | sudo tee -a /etc/sudoers
+echo `whoami` ALL=NOPASSWD: ALL | sudo tee -a /etc/sudoers > /dev/null
 sudo sed -i -e 's/Default/#Default/' /etc/sudoers
-sudo sed -i -e 's/ubuntu/mininet-vm/' /etc/hostname
+echo mininet-vm | sudo tee /etc/hostname > /dev/null
 sudo sed -i -e 's/ubuntu/mininet-vm/g' /etc/hosts
 sudo hostname `cat /etc/hostname`
 sudo sed -i -e 's/quiet splash/text/' /etc/default/grub
 sudo update-grub
+# 12.10 and earlier
 sudo sed -i -e 's/us.archive.ubuntu.com/mirrors.kernel.org/' \
 	/etc/apt/sources.list
+# 13.04 and later
 sudo sed -i -e 's/\/archive.ubuntu.com/\/mirrors.kernel.org/' \
 	/etc/apt/sources.list
 sudo apt-get update