
See
http://linuxcnc.org/docs/html/getting-started/updating-linuxcnc.html#cha:updating-linuxcnc
1. Upgrade to the new version

1.1. Setting apt sources  << Excellent howTo Software Source 
For ubuntu 12.04  
Use Ubuntu Precise  	
deb http://linuxcnc.org precise base 2.7-rtai

In the Ubuntu Software Center window, click on the Edit menu, then click on Software Sources... to open the Software Sources window. 
or 
Use Applicaitons -> System Tools -> Admininistration -> Update Manager 
After the Gui settles click "Settings"


1.2 skip


1.3. Ubuntu Precise << actual install 


For updare to v2.8.11 pre-release 
Do step 1.1 and step 1.3 
except 
change the wheesy to precise for the mobot <see apt/sources.ist.d 


try the software update manager.    If authenitcation issue 


WARNING: The following packages cannot be authenticated!
  linuxcnc linuxcnc-doc-en
E: There are problems and -y was used without --force-yes



see
https://askubuntu.com/questions/42227/how-do-i-force-apt-get-to-update-the-state-of-package-versions


WARNING: The following packages cannot be authenticated!
  linuxcnc linuxcnc-doc-en
E: There are problems and -y was used without --force-yes

https://linux.die.net/man/8/apt-get
sudo apt-get update -y
sudo apt-get upgrade --force-yes
sudo apt-get install -y




