Ubuntu Doc page says this:

It is advisable that you add the Opera GPG key.

wget -qO - http://deb.opera.com/archive.key | sudo apt-key add -

Where do I add that?

I want to take the advice but I don't know what part of software center to add gpg keys to.

  • 3
    I believe that is a one line command to enter into terminal
    – Mateo
    Commented May 5, 2013 at 13:55
  • 1
    .msi in Ubuntu is called .deb.
    – Alvar
    Commented May 5, 2013 at 17:12
  • 6
    As a side note, adding keys you fetch over non-HTTPS breaks any security that signing packages added. Wherever possible, you should download keys over a secure channel (https://).
    – user304335
    Commented Jul 10, 2014 at 18:00
  • 5
    Do not use apt-key
    – user307747
    Commented May 18, 2021 at 18:10

8 Answers 8


Note from Moderators: This solution is no longer functional since apt-key has been deprecated. However, there is no capability to change if a message is accepted or not, other than deletion of the answer, and for historical reasons AND the massive number of upvotes since the original post in 2013 prevent us from deleting this post.

Please do not raise flags regarding "insecure" and "deprecated" natures of this answer.

This a a one line command to enter in terminal. See What is a terminal and how do I open and use it?

To use it, you would paste the entire command in the terminal (remember to use https):

wget -qO - https://deb.opera.com/archive.key | sudo apt-key add -

But of course, it is daunting just copying and pasting commands without knowing what they are doing, and having no instructions on how to undo their actions, so here is a basic breakdown of the commands:

  • wget downloads something from a server. See wget manual for Ubuntu 16.04.
  • | is a pipline, which takes the output of one command and runs it into the input of another
  • apt-key add adds a package key

So it basically downloads the key and then adds it in one command.

I tested the command and it should work.

Now to verify that it worked, run this command (from this answer):

apt-key list

This will list the keys added and the key from Opera should be listed on the bottom like this:

pub   1024D/30C18A2B 2012-10-29 [expires: 2014-10-29]
uid                  Opera Software Archive Automatic Signing Key 2013 <[email protected]>
sub   4096g/C528FCA9 2012-10-29 [expires: 2014-10-29]

The linked answer also shows that you can remove the key if needed, using:

sudo apt-key del 30C18A2B

with 30C18A2B being the key-id from the list.

After performing that command, and setting up the sources exactly like in your screen-shot, do:

sudo apt-get update
sudo apt-get install opera

(note there are some random warnings, but nothing that affects the install or software center operations)

And for the removal (just in case): What is the correct way to completely remove an application?

So in summary:

  • Add repository enter image description here
  • Add key with apt-key
  • Install in terminal with apt-get
  • Search in dash enter image description here
  • 4
    "apt-key adv" allows one to download the key from a public keyserver.
    – jeremiah
    Commented Mar 31, 2016 at 13:27
  • After adding the key with apt-key add, the .key file (in this case, "archive.key") can be deleted without consequence, right? The key (the information, not the file) has already been added to a list somewhere, so the file should no longer be needed.
    – Cerran
    Commented Mar 17, 2018 at 20:52
  • 3
    @Cerran, correct. APT keeps keys somewhere else (/etc/apt/trusted.gpg.d/ and /var/lib/apt/keyrings/ for example.) Commented Feb 27, 2019 at 18:36
  • 1
    If you get an SSL error with wget, you can use curl instead: curl -L https://deb.opera.com/archive.key | sudo apt-key add -
    – rubo77
    Commented May 6, 2019 at 9:54
  • Isn't apt-key deprecated? I keep seeing this warning everywhere. Here, for example (installation guide for Nvidia Cuda): docs.nvidia.com/cuda/archive/11.7.1/…
    – GuiMendel
    Commented Nov 29, 2022 at 15:03

If you are manually adding a key from a PPA, use:

sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 00000000

Alternatively, if you do not want to use apt-key:

sudo gpg --keyserver hkp://keyserver.ubuntu.com:80 --no-default-keyring --keyring /usr/share/keyrings/change-ppa-name-here.gpg --recv-keys 00000000

Replace the 00000000 with the second part of the key informed in the PPA website that you want to add.

For example, if you find this line:


Use only the second part (no matter its size), which in this example is 7BF576066

  • are errors like gpg: keyserver receive failed: No keyserver available and gpg: keyserver receive failed: Connection refused common?
    – iuridiniz
    Commented Dec 31, 2018 at 13:49
  • No, errors like these aren't common. Maybe you're writing the wrong key. Commented Jan 1, 2019 at 14:51
  • 4
    equivalent without apt-key: sudo gpg --keyserver hkp://keyserver.ubuntu.com:80 --no-default-keyring --keyring /usr/share/keyrings/my-ppa.gpg --recv-keys 00000000
    – eddygeek
    Commented Sep 4, 2022 at 22:08
  • 1
    FYI eddygeeks comment works. This should be a full answer. BUT I had already populated my-ppa.gpg with incorrect instructions from elsewhere on the Intertubes. I first had to remove the old-style my-ppa.gpg. I got errors when following this procedure without removing the file. Commented Sep 12, 2023 at 16:41
  • 1
    Thanks @JoshuaClayton , I updated the answer Commented Sep 12, 2023 at 21:05

Newer versions of apt also support the following:

apt-key adv --fetch-keys http://deb.opera.com/archive.key

This method also provides more detailed feedback as well, e.g.:

gpg: key 7BD9BF62: public key "signing key <[email protected]>" imported
gpg: Total number processed: 1
gpg:               imported: 1  (RSA: 1)

This also has the added bonus of removing the need for additional dependencies like wget or curl.

  • 1
    apt-key adv does not seem to work for https Commented Jun 14, 2017 at 11:24
  • 5
    @dani-h You need gnupg-curl to use HTTPS if you are using GPG 1.x.
    – Tao Wang
    Commented Oct 27, 2017 at 5:08
  • 1
    apt-key adv --fetch-keys will only fetch one key from the URL, and if the URL contains multiple keys, please use wget | apt-key add instead.
    – Tao Wang
    Commented Oct 27, 2017 at 5:11
  • 1
    It seems to work with https already (just tested on Ubuntu 17.10) Commented Dec 9, 2018 at 19:25

apt-key now seems to be deprecated, I have created a script that will detect and get the missing keys, you can get it here.

#!/bin/sh -e
sudo apt-get update 2>&1 | sed -En 's/.*NO_PUBKEY ([[:xdigit:]]+).*/\1/p' | sort -u > "${tmp}"
cat "${tmp}" | xargs sudo gpg --keyserver "hkps://keyserver.ubuntu.com:443" --recv-keys  # to /usr/share/keyrings/*
cat "${tmp}" | xargs -L 1 sh -c 'sudo gpg --yes --output "/etc/apt/trusted.gpg.d/$1.gpg" --export "$1"' sh  # to /etc/apt/trusted.gpg.d/*
rm "${tmp}"

You should not add third-party keys via apt-key add. These keys can then be used to sign any package on your machine, including those from the archive. Now you should only allow the key to sign only a specific package. Complete answer on UNIX.SE from user Trudy.


Let's say you want to add docker's repo key (an ASCII-armored key):

$ curl -fsSL https://download.docker.com/linux/ubuntu/gpg \
    | sudo gpg --dearmor -o /etc/apt/keyrings/docker.gpg

If you're not sure if the key is ASCII-armored:

$ curl -fsSL https://download.docker.com/linux/ubuntu/gpg | file -
/dev/stdin: PGP public key block Public-Key (old)

For a non-armored key the output will be along the lines of:

/dev/stdin: OpenPGP Public Key Version 4, Created ..., RSA (Encrypt or Sign, 4096 bits); User ID; Signature; OpenPGP Certificate

And to add it you need:

$ sudo curl -fsSL https://... -o /etc/apt/keyrings/NAME.gpg

More on it can be found here. But it suggests to install keys to /usr/share/keyrings, which is the location for package maintainers. More on it below.

For apt < 2.4.0 you need to create /etc/apt/keyrings before adding the key (Debian link):

apt (2.4.0) unstable; urgency=medium ...

  • Install an empty /etc/apt/keyrings directory. This directory is intended to provide an alternative to /usr/share/keyrings for placing keys used with signed-by.

That means before Ubuntu 22.04 Jammy, Debian 12 Bookworm.

Deprecating apt-key is a security measure. You can learn more on it here. As such, adding files to /etc/apt/trusted.gpg.d is also insecure. Because /etc/apt/trusted.gpg.d is a way to add keys to the keyring (/etc/apt/trusted.gpg) w/o apt-key add, by copying files.

Also note that:

The recommended locations for keyrings are /usr/share/keyrings for keyrings managed by packages, and /etc/apt/keyrings for keyrings managed by the system operator.

apt-key is deprecated since 2.1.8 (Debian link):

apt (2.1.8) unstable; urgency=medium ...

  • Fully deprecate apt-key, schedule removal for Q2/2022

In terms of releases that would be Ubuntu 21.10 Impish, Debian 11 Bullseye. The commit (Debian link).

Ability to specify signed-by in apt sources was added in 1.1.exp9 (Debian link):

apt (1.1~exp9) experimental; urgency=medium ...

  • implement Signed-By option for sources.list

The commit (Debian link).


Another way where you just have an .asc key, you download the .asc key and add it to the keyring.

For instance -

curl -L https://packages.riot.im/debian/repo-key.asc | sudo apt-key add -

Make sure to "dearmor" (aka convert to binary) before storing your pgp key in trusted.gpg.d:

cat mykey.gpg | gpg --dearmor > /etc/apt/trusted.gpg.d/mykey.gpg

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