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I wrote :

~$ do-release-upgrade

and the system says:

  Checking for a new ubuntu release   
   Get:1 Upgrade tool signature [198 B]                                              
   Get:2 Upgrade tool [1551 kB]                                                   
   Fetched 1551 kB in 6s (167 kB/s)                                                
   extracting 'precise.tar.gz'   
   authenticate 'precise.tar.gz' against 'precise.tar.gz.gpg'   
   exception from gpg: GnuPG exited non-zero, with code 2   
   Debug information: 

   gpg: Signature made Thu 11 Oct 2012 07:47:10 AM EET using DSA key ID 437D05B5  
   gpg: can't open `/etc/apt/trusted.gpg'  
   gpg: keydb_search failed: file open error       
   gpg: Can't check signature: public key not found

   Authentication failed   
   Authenticating the upgrade failed. There may be a problem with the network or with the server. 

Please help me!

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up vote 3 down vote accepted

When trying to do any administrative task like installing an application or upgrading the system, you will always need to have administrative rights. This can be achieved in several ways, 2 of them are:

  1. To actually BE the root user (Not recommended. Too much power in your hands. /godmode 1)

  2. Prefix any command line with the command sudo.

In your case I recommend doing the second option. And to be sure, do a clean upgrade like this (This way you have less chance to come up with a bug while doing the upgrade, before it or after the upgrade).

sudo apt-get update && sudo apt-get upgrade

After everything is done then execute the following:

sudo apt-get dist-upgrade

This way you can see if the system is ok before doing the version upgrade.

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Run these commands:

sudo apt-key adv --recv-keys --keyserver 40976EAF437D05B5
sudo apt-key adv --recv-keys --keyserver 3B4FE6ACC0B21F32

This downloads the missing GPG keys (as mentioned in the original error message) from the Ubuntu GPG keyserver.

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