How do I fix the GPG error "NO_PUBKEY"?

You need to get and import the key.

To get the key from a PPA, visit the PPA’s Launchpad page. On every PPA page at Launchpad you will find this link (2), after clicking on ‘Technical details about this PPA’ (1):

Follow it and click on the key ID link (3):

Save the page, this is your key file.

Now it’s time to import it:

• Applications > Software Center,
• Edit > Software sources...,
• Enter your password,
• Go to the Authentication tab and click on Import Key File..., finally
• Select the saved key file and click on OK.

More generally, the following method should work for every repository. First of all search, with eventual help of a search engine, for a text on the program provider’s website looking like the following:

-----BEGIN PGP PUBLIC KEY BLOCK-----
Version: GnuPG v1.4.1 (GNU/Linux)
[...]
-----END PGP PUBLIC KEY BLOCK-----

Such a text is for example displayed on http://deb.opera.com. Copy the passage, paste it in an empty file that you create on your desktop. This results in the key file.

Then continue with the importation of the key:

• Applications > Sofware Center
• Edit > Sofware sources…, enter password
• Authentication tab, click on ‘Import Key File…’
• Select the saved key file and click on ‘Ok’.

You may now remove the previously created key file.

This answer was valid for Ubuntu 20.04 and previous versions. For Ubuntu 20.10 and later versions, see this answer on StackOverflow.

The short version is:

sudo mkdir -m 0755 -p /etc/apt/keyrings/ 

wget -O- https://example.com/EXAMPLE.gpg |
    gpg --dearmor |
    sudo tee /etc/apt/keyrings/EXAMPLE.gpg > /dev/null
    sudo chmod 644 /etc/apt/keyrings/EXAMPLE.gpg

echo "deb [signed-by=/etc/apt/keyrings/EXAMPLE.gpg] https://example.com/apt stable main" |
    sudo tee /etc/apt/sources.list.d/EXAMPLE.list
    sudo chmod 644 /etc/apt/sources.list.d/EXAMPLE.list

# Optional (you can find the email address / ID using 'apt-key list')
sudo apt-key del support@example.com

Original answer:

Execute the following commands in terminal

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys <PUBKEY>

where <PUBKEY> is your missing public key for repository, e.g. 8BAF9A6F.

Then update

sudo apt-get update

ALTERNATE METHOD:

sudo gpg --keyserver pgpkeys.mit.edu --recv-key  <PUBKEY>
sudo gpg -a --export <PUBKEY> | sudo apt-key add -
sudo apt-get update

Note that when you import a key like this using apt-key you are telling the system that you trust the key you’re importing to sign software your system will be using. Do not do this unless you’re sure the key is really the key of the package distributor.

It happens when you don’t have a suitable public key for a repository.

To solve this problem use this command:

gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv 9BDB3D89CE49EC21

which retrieves the key from ubuntu key server. And then this:

gpg --export --armor 9BDB3D89CE49EC21 | sudo apt-key add -

which adds the key to apt trusted keys.

The solution can be found here & here & here.

There is a tiny script packaged in the WebUpd8 PPA which I’ll link as a single .deb download so you don’t have to add the whole PPA – which automatically imports all missing GPG keys.

Download and install Launchpad-getkeys (ignore the ~natty in its version, it works with all Ubuntu versions from Karmic all the way to Oneiric). Once installed, open a terminal and type:

sudo launchpad-getkeys

If you’re behind a proxy, things are a bit more complicated so see this for more info

I faced the same issue while installing Heroku. The link below solved my problem –

http://naveenubuntu.blogspot.in/2011/08/fixing-gpg-keys-in-ubuntu.html

After fixing the NO_PUBKEY issue, the below issue remained

W: GPG error: xhttp://toolbelt.heroku.com ./ Release: The following signatures were invalid: BADSIG C927EBE00F1B0520 Heroku Release Engineering <release@heroku.com>

To fix it I executed the following commands in terminal:

sudo -i  
apt-get clean  
cd /var/lib/apt  
mv lists lists.old  
mkdir -p lists/partial  
apt-get clean  
apt-get update  

Source – Link to solve it

_{note: As of recent versions, it is no longer considered good practice to add PPA keys to the keyring. However, I will leave this answer but apt-key is now deprecated so it is recommended we follow different methods for now.}

apt can only handle 40 keys in /etc/apt/trusted.gpg.d . 41 keys and you will get the GPG error "no public key found" even if you go through all the steps to add the missing key(s).

Check to see if there are any unused keys in this file from ppa(s) you no longer use. If all are in use, consider removing some ppa(s) along with the corresponding keyfiles in /etc/apt/trusted.gpg.d

Furthermore, using

sudo apt-key adv

Is considered a security risk and is not recommended as you are "undermining the whole security concept as this is not a secure way of recieving keys for various reasons (like: hkp is a plaintext protocol, short and even long keyids can be forged, …)". http://ubuntuforums.org/showthread.php?t=2195579

I believe the correct way to add missing keys (for example 1ABC2D34EF56GH78) is

gpg --keyserver hkp://keyserver.ubuntu.com:80 --recv 1ABC2D34EF56GH78
gpg --export --armor 1ABC2D34EF56GH78 | sudo apt-key add -

I had the same problem with DynDNS’s Updater client.

Turns out it was just expired keys.

Reinstalling the software (downloading a new .deb from the website, then using Software Centre to reinstall) fixed the problem.

Error message for reference:

W: GPG error: http://cdn.dyn.com stable/ Release: The following signatures were invalid: KEYEXPIRED 141943.......

Good! I finaly found the way!

I’ve tested all method’s to fix GPG error NO_PUBKEY and nothing working for me.

I’ve deleted the entire contents of the folder /etc/apt/trusted.gpg.d

cd /etc/apt/trusted.gpg.d
sudo rm -R *
sudo apt-get update

And I use the Y-PPA-Manager method because I’m too lazy to create all pubkey’s manually (too many): http://www.unixmen.com/fix-w-gpg-error-no_pubkey-ubuntu/

run sudo apt-get update again and finaly all work great now! Tanks!

Based Source : post #17 on https://bugs.launchpad.net/ubuntu/+source/apt/+bug/1263540

Make sure you have apt-transport-https installed:

dpkg -s apt-transport-https > /dev/null || bash -c "sudo apt-get update; 
sudo apt-get install apt-transport-https -y" 

Add repository:

curl https://repo.skype.com/data/SKYPE-GPG-KEY | sudo apt-key add - 
echo "deb [arch=amd64] https://repo.skype.com/deb stable main" | sudo tee /etc/apt/sources.list.d/skype-stable.list 

Install Skype for Linux:

sudo apt-get update 
sudo apt-get install skypeforlinux -y

Source: https://community.skype.com/t5/Linux/Skype-for-Linux-Beta-signatures-couldn-t-be-verified-because-the/td-p/4645756

This error can also occur when the apt list file by the PPA points to a local keyring, like

deb [signed-by=/usr/share/keyrings/SOMETHING.gpg] https://download.something.org/something something/

And while that file may exist on your system (possibly downloaded with a prior command), it may be unreadable due to missing permissions. I just fixed this kind of error by running

chmod 644 /usr/share/keyrings/*

after having fetched the keyring file. The underlying issue was the usage of sudo when I already was root user. Really weird as all of this is root anyway and there was no access permission failure message anywhere… but that fixed it

2021 August. This is what worked for me.

cd /etc/apt/trusted.gpg.d
sudo rm -R *
sudo apt-get update

The last line will raise errors of missing keys.

What you’d then have to do is manually install each of the keys listed in the errors
for example if the error is saying that your missing PUB_KEY is 9BDB3D89CE49EC21,

You can manually add the Key with the command sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 9BDB3D89CE49EC21

Re-run sudo apt-get update

Repeat the process for the new key raised in the error

Say if the new key was 3BDB3D89CE49EC24,
Just Manually add the Key with the command sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 3BDB3D89CE49EC24

Re-run sudo apt-get update and repeat the process until all the errors are gone.

Then go back to the package site you were trying to install and repeat the installation process.

For my case, the error was coming while I tried installing Sublime Text
Doing the above and returning to the Sublime installation guide here solved the issues.

Don’t forget to upvote if this works for you. And it must do

Updated version (Ubuntu 22.04 LTS)

Because apt-key is deprecated now, and you want to use /etc/apt/trusted.gpg.d/, you can use

sudo gpg --keyserver pgpkeys.mit.edu --recv-key <PUBKEY>
sudo mkdir -p /etc/apt/keyrings/
sudo gpg -a --export <PUBKEY> /etc/apt/keyrings/<your-keyfile-name>.gpg
# now go to your /etc/apt/sources.list.d/<source definition list file>, and 
# add [signed-by=/etc/apt/keyrings/<your-keyfile-name>.gpg] between deb and url like this:
# deb <add here> https://...

<PUBKEY> is the 8 character fingerprint like 210976F2 and <target name> is a name of your choice by which you will know that key.

EDIT: Updated for more security, taken from a lengthy answer