"Docker Pull" Certificate Signed by Unknown Authority

• first create an empty json file

  cat << EOF > /etc/docker/daemon.json
  { }
  EOF
  

• than run the following to add certs

  openssl s_client -showcerts -connect [registry_address]:[registry_port] < /dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > /etc/docker/certs.d/[registry_address]/ca.crt
  

works without restart

OR

import the cert to system like

• save the cert to the file , like the command above (the port is crucial, no need for the protocol)

  openssl s_client -showcerts -connect [registry_address]:[registry_port] < /dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > ca.crt
  

• copy it to /usr/local/share/ca-certificates/

  sudo cp ca.crt /usr/local/share/ca-certificates/
  

• run update-ca-certificates

  sudo update-ca-certificates
  

• restart docker !

Here is a quick solution:

• Edit or create the file /etc/docker/daemon.json and add insecure-registries:

example for docker.squadwars.org:

{
    "insecure-registries" : ["docker.squadwars.org:443"]
}

• Restart docker daemon

systemctl restart docker

• Create a directory with the same name of the host .

example for docker.squadwars.org:

mkdir -p /etc/docker/certs.d/docker.squadwars.org

• Get the certificate and save it to the created directory.

ex +’/BEGIN CERTIFICATE/,/END CERTIFICATE/p’ <(echo | openssl s_client -showcerts -connect docker.squadwars.org:443) -scq > /etc/docker/certs.d/

For the MacOS Docker Desktop user:

Go to your repository's URL in a browser. You may have to accept all security prompts.

Click on the padlock 🔓on the address bar, then click on "Connection is secure/Certificate is valid" (on Chrome) or "Show Certificate" (on Safari), and a certificate window popup will appear.

Click and hold down on the big paper icon of the certificate and drag it to a folder of your preference, or the desktop.

Open your terminal (make sure to replace the last argument with the location of your file):

security add-trusted-cert -d -r trustRoot -k ~/Library/Keychains/login.keychain-db ~/<<<somefolder>>>/<<<yourserver.cer>>>

Restart your docker engine.

For my case, the error was on "docker login" command.

The solution I found for my ubuntu:

I downloaded the crt file via firefox (lock icon in the url adress bar) and save it : ~/mydomain:1234.crt

After that :

cp ~/mydomain:1234.crt /usr/local/share/ca-certificates/
update-ca-certificates
service docker restart

For me I ended up doing this to get it to work:

sudo cp -p abc.crt /etc/pki/ca-trust/source/anchors
sudo update-ca-trust
sudo update-ca-trust extract
sudo systemctl daemon-reload
sudo systemctl restart docker

For anyone who is using CentOS 7, this is what worked for me:

• Obtain necessary certificate (e.g. from your company)
• Copy the certificate to ca-trust location:

sudo cp -p abc.crt /etc/pki/ca-trust/source

• Update the certificate:

sudo update-ca-trust extract

• Reload daemon and restart docker:

sudo systemctl daemon-reload
sudo systemctl restart docker

Didn't see this mentioned in any of the answers. Here is the official docker documentation for setting up certs for each specific domain. This goes along with the most accepted answer.

Path for:

• Linux: /etc/docker/certs.d/[domain of relevent cert]/[cert].crt
• Windows: C:/ProgramData/Docker/certs.d/[domain of relevent cert]/[cert].crt

If you are using WSL or WSL2 you will place the cert in the windows location.

A key problem that I encountered was that the extension of the cert is important to docker. I was not able to resolve the issue with a .cer ssl cert but was with .crt.

By default docker keeps a local Certificate store, in Centos:/etc/sysconfig/docker. In Organizations, the servers usually comes preinstalled with it's own Root Cert. So if you use cert issued by the organization, docker will not be able to find the organization's Root Cert. when it refers to its local store. So either you can remove the reference to its local store in /etc/sysconfig/docker or you can delete it's local Certificate store (Centos:/etc/docker/certs.d). Restarting docker service after you make the change will resolve this issue.

In my case I had the same problem inside a KIND container. Curl didn't work there.

curl 
curl: (60) SSL certificate problem: unable to get local issuer certificate
More details here: 

curl failed to verify the legitimacy of the server and therefore could not
establish a secure connection to it. To learn more about this situation and
how to fix it, please visit the web page mentioned above.
    

and the update-ca-certificate command didn't work for me. I had to append the CA certificate to the /etc/ssl/certs/ca-certificates.crt file:

cat /ca_cert.pem >>  /etc/ssl/certs/ca-certificates.crt

And then curl worked properly.

update ca without restart docker,and use root ca.cert, replace registry.clickpaas.tech with your domain:

sudo yum -y update ca-certificates;
sudo mkdir -p /etc/docker/certs.d/
sudo cp /etc/ssl/certs/ca-bundle.crt /etc/docker/certs.d/

for Ubuntu 20

sudo update-ca-certificates --fresh

openssl s_client -showcerts -verify 5 -connect registry-1.docker.io:443 < /dev/null 2>/dev/null | openssl x509 -outform PEM | tee ~/docker.crt

openssl s_client -showcerts -verify 5 -connect production.cloudflare.docker.com:443 < /dev/null 2>/dev/null | openssl x509 -outform PEM | tee ~/docker-com.crt

sudo cp ~/docker-com.crt /usr/local/share/ca-certificates/.

sudo cp ~/docker.crt /usr/local/share/ca-certificates/


sudo update-ca-certificates
sudo service docker restart