this is obsolete doc -- see http://doc.nethence.com/ instead

Maintaining Ubuntu workstations 

See http://pbraun.nethence.com/sysutils_linux/debian.html for anything that's common with Debian. 

Basic system 

Check the release version, 

  lsb_release -a 

Proceed with a minor upgrade, 

  apt update 

  apt-get full-upgrade 

Proceed with a major upgrade, 

  do-release-upgrade 

Note. add -d to proceed even for development / alpha / beta releases 

Desktop Environment 

Reinstall the desktop environment, 

  apt-get install --reinstall ubuntu-desktop 

  #apt-get install --reinstall unity 

Miscellaneous 

Eventually disable the firewall and check, 

  #ufw disable 

  #iptables -L -n 

Ref. http://www.cyberciti.biz/faq/ubuntu-server-disable-firewall/ 

Disable graphical login on ubuntu server 12 LTS, 

  service lxdm stop 

  update-rc.d -f lxdm remove 

Disable graphical login on ubuntu 14 LTS, 

service lightdm stop 

update-rc.d -f lightdm remove 

Disable graphical login on Ubuntu 15, 

  systemctl stop lightdm 

  systemctl disable lightdm