gpgkeys: ключевой F60F4B3D7FA2AF80, не найденный на keyserver

Как я могу устранить эту проблему?

mona@pascal:~$ sudo apt-get update
Ign file:  InRelease
Get:1 file:  Release.gpg [181 B]                                               
Get:2 file:  Release [196 B]                                                   
Ign file:  Translation-en_US                                                   
Ign file:  Translation-en                                                      
Hit http://storage.googleapis.com stable InRelease                             
Hit http://storage.googleapis.com stable/jdk1.8 amd64 Packages                 
Ign http://us.archive.ubuntu.com trusty InRelease                              
Get:3 http://us.archive.ubuntu.com trusty-updates InRelease [65.9 kB]          
Hit http://ppa.launchpad.net trusty InRelease                                  
Get:4 http://security.ubuntu.com trusty-security InRelease [65.9 kB]           
Hit http://ppa.launchpad.net trusty/main amd64 Packages                        
Get:5 http://us.archive.ubuntu.com trusty-backports InRelease [65.9 kB]        
Ign http://developer.download.nvidia.com  InRelease                            
Get:6 http://developer.download.nvidia.com  Release.gpg [819 B]                
Hit http://developer.download.nvidia.com  Release                              
Ign http://developer.download.nvidia.com  Release                              
Hit http://us.archive.ubuntu.com trusty Release.gpg                            
Hit http://ppa.launchpad.net trusty/main i386 Packages                         
Get:7 http://us.archive.ubuntu.com trusty-updates/main Sources [383 kB]        
Hit http://ppa.launchpad.net trusty/main Translation-en                        
Ign http://storage.googleapis.com stable/jdk1.8 Translation-en_US              
Get:8 http://security.ubuntu.com trusty-security/main Sources [120 kB]         
Ign http://developer.download.nvidia.com  Packages/DiffIndex                   
Ign http://storage.googleapis.com stable/jdk1.8 Translation-en                 
Get:9 http://us.archive.ubuntu.com trusty-updates/restricted Sources [5,360 B] 
Get:10 http://us.archive.ubuntu.com trusty-updates/universe Sources [166 kB]   
Get:11 http://security.ubuntu.com trusty-security/restricted Sources [4,064 B] 
Get:12 http://security.ubuntu.com trusty-security/universe Sources [43.6 kB]   
Get:13 http://us.archive.ubuntu.com trusty-updates/multiverse Sources [7,520 B]
Get:14 http://security.ubuntu.com trusty-security/multiverse Sources [3,190 B] 
Get:15 http://us.archive.ubuntu.com trusty-updates/main amd64 Packages [901 kB]
Get:16 http://security.ubuntu.com trusty-security/main amd64 Packages [531 kB] 
Get:17 http://security.ubuntu.com trusty-security/restricted amd64 Packages [13.0 kB]
Get:18 http://security.ubuntu.com trusty-security/universe amd64 Packages [138 kB]
Get:19 http://us.archive.ubuntu.com trusty-updates/restricted amd64 Packages [15.9 kB]
Get:20 http://us.archive.ubuntu.com trusty-updates/universe amd64 Packages [376 kB]
Get:21 http://security.ubuntu.com trusty-security/multiverse amd64 Packages [5,198 B]
Get:22 http://security.ubuntu.com trusty-security/main i386 Packages [493 kB]  
Get:23 http://us.archive.ubuntu.com trusty-updates/multiverse amd64 Packages [15.0 kB]
Get:24 http://us.archive.ubuntu.com trusty-updates/main i386 Packages [861 kB] 
Get:25 http://security.ubuntu.com trusty-security/restricted i386 Packages [12.7 kB]
Get:26 http://security.ubuntu.com trusty-security/universe i386 Packages [138 kB]
Hit http://developer.download.nvidia.com  Packages                             
Get:27 http://security.ubuntu.com trusty-security/multiverse i386 Packages [5,339 B]
Get:28 http://us.archive.ubuntu.com trusty-updates/restricted i386 Packages [15.6 kB]
Get:29 http://us.archive.ubuntu.com trusty-updates/universe i386 Packages [377 kB]
Ign http://developer.download.nvidia.com  Translation-en_US                    
Hit http://security.ubuntu.com trusty-security/main Translation-en             
Hit http://security.ubuntu.com trusty-security/multiverse Translation-en       
Hit http://security.ubuntu.com trusty-security/restricted Translation-en       
Ign http://developer.download.nvidia.com  Translation-en                       
Get:30 http://us.archive.ubuntu.com trusty-updates/multiverse i386 Packages [15.5 kB]
Hit http://security.ubuntu.com trusty-security/universe Translation-en         
Hit http://us.archive.ubuntu.com trusty-updates/main Translation-en       
Hit http://us.archive.ubuntu.com trusty-updates/multiverse Translation-en   
Hit http://us.archive.ubuntu.com trusty-updates/restricted Translation-en
Hit http://us.archive.ubuntu.com trusty-updates/universe Translation-en
Get:31 http://us.archive.ubuntu.com trusty-backports/main Sources [9,626 B]
Get:32 http://us.archive.ubuntu.com trusty-backports/restricted Sources [28 B]
Get:33 http://us.archive.ubuntu.com trusty-backports/universe Sources [35.2 kB]
Get:34 http://us.archive.ubuntu.com trusty-backports/multiverse Sources [1,898 B]
Get:35 http://us.archive.ubuntu.com trusty-backports/main amd64 Packages [13.3 kB]
Get:36 http://us.archive.ubuntu.com trusty-backports/restricted amd64 Packages [28 B]
Get:37 http://us.archive.ubuntu.com trusty-backports/universe amd64 Packages [43.2 kB]
Get:38 http://us.archive.ubuntu.com trusty-backports/multiverse amd64 Packages [1,571 B]
Get:39 http://us.archive.ubuntu.com trusty-backports/main i386 Packages [13.3 kB]
Get:40 http://us.archive.ubuntu.com trusty-backports/restricted i386 Packages [28 B]
Get:41 http://us.archive.ubuntu.com trusty-backports/universe i386 Packages [43.2 kB]
Get:42 http://us.archive.ubuntu.com trusty-backports/multiverse i386 Packages [1,552 B]
Hit http://us.archive.ubuntu.com trusty-backports/main Translation-en
Hit http://us.archive.ubuntu.com trusty-backports/multiverse Translation-en
Hit http://us.archive.ubuntu.com trusty-backports/restricted Translation-en
Hit http://us.archive.ubuntu.com trusty-backports/universe Translation-en
Hit http://us.archive.ubuntu.com trusty Release   
Hit http://us.archive.ubuntu.com trusty/main Sources
Hit http://us.archive.ubuntu.com trusty/restricted Sources
Hit http://us.archive.ubuntu.com trusty/universe Sources
Hit http://us.archive.ubuntu.com trusty/multiverse Sources
Hit http://us.archive.ubuntu.com trusty/main amd64 Packages
Hit http://us.archive.ubuntu.com trusty/restricted amd64 Packages
Hit http://us.archive.ubuntu.com trusty/universe amd64 Packages
Hit http://us.archive.ubuntu.com trusty/multiverse amd64 Packages
Hit http://us.archive.ubuntu.com trusty/main i386 Packages
Hit http://us.archive.ubuntu.com trusty/restricted i386 Packages
Hit http://us.archive.ubuntu.com trusty/universe i386 Packages
Hit http://us.archive.ubuntu.com trusty/multiverse i386 Packages
Hit http://us.archive.ubuntu.com trusty/main Translation-en
Hit http://us.archive.ubuntu.com trusty/multiverse Translation-en
Hit http://us.archive.ubuntu.com trusty/restricted Translation-en
Hit http://us.archive.ubuntu.com trusty/universe Translation-en
Ign http://us.archive.ubuntu.com trusty/main Translation-en_US                 
Ign http://us.archive.ubuntu.com trusty/multiverse Translation-en_US           
Ign http://us.archive.ubuntu.com trusty/restricted Translation-en_US           
Ign http://us.archive.ubuntu.com trusty/universe Translation-en_US             
Fetched 5,007 kB in 7s (679 kB/s)                                              
Reading package lists... Done
W: GPG error: http://developer.download.nvidia.com  Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY F60F4B3D7FA2AF80

и затем я использовал этот метод здесь: https://chrisjean.com/fix-apt-get-update-the-following-signatures-couldnt-be-verified-because-the-public-key-is-not-available/

mona@pascal:~$ sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-key F60F4B3D7FA2AF80
Executing: gpg --ignore-time-conflict --no-options --no-default-keyring --homedir /tmp/tmp.TwDO5GWCyw --no-auto-check-trustdb --trust-model always --keyring /etc/apt/trusted.gpg --primary-keyring /etc/apt/trusted.gpg --keyring /etc/apt/trusted.gpg.d/webupd8team-java.gpg --keyserver keyserver.ubuntu.com --recv-key F60F4B3D7FA2AF80
gpg: requesting key 7FA2AF80 from hkp server keyserver.ubuntu.com
gpgkeys: key F60F4B3D7FA2AF80 not found on keyserver
gpg: no valid OpenPGP data found.
gpg: Total number processed: 0

Я также использовал другое решение, предоставленное в сети, однако все еще получают ту же ошибку:

mona@pascal:~$ sudo apt-key del F60F4B3D7FA2AF80
OK

и:

mona@pascal:~$ gpg --keyserver hkp://keyserver.ubuntu.com --search-keys F60F4B3D7FA2AF80
gpg: directory `/home/mona/.gnupg' created
gpg: new configuration file `/home/mona/.gnupg/gpg.conf' created
gpg: WARNING: options in `/home/mona/.gnupg/gpg.conf' are not yet active during this run
gpg: keyring `/home/mona/.gnupg/secring.gpg' created
gpg: keyring `/home/mona/.gnupg/pubring.gpg' created
gpg: searching for "F60F4B3D7FA2AF80" from hkp server keyserver.ubuntu.com
gpg: key "F60F4B3D7FA2AF80" not found on keyserver

Я не могу также экспортировать его

mona@pascal:~$ gpg -a --export F60F4B3D7FA2AF80
gpg: WARNING: nothing exported