openssl s_client -connect host.host:9999

depth=1 /C=NZ/ST=Test State or Province/O=Organization Name/OU=Organizational Unit Name/CN=Test CA
verify error:num=19:self signed certificate in certificate chain
verify return:0
23177:error:14094410:SSL routines:SSL3_READ_BYTES:sslv3 alert handshake failure:s3_pkt.c:1086:SSL alert number 40
23177:error:140790E5:SSL routines:SSL23_WRITE:ssl handshake failure:s23_lib.c:188:

-showcerts

-CApath /etc/ssl/certs/

With SNI

If the remote server is using SNI (that is, sharing multiple SSL hosts on a single IP address) you will need to send the correct hostname in order to get the right certificate.

openssl s_client -showcerts -servername www.example.com -connect www.example.com:443 </dev/null

Without SNI

If the remote server is not using SNI, then you can skip -servername parameter:

openssl s_client -showcerts -connect www.example.com:443 </dev/null

To view the full details of a site's cert you can use this chain of commands as well:

$ echo | \
    openssl s_client -servername www.example.com -connect www.example.com:443 2>/dev/null | \
    openssl x509 -text

It turns out there is more complexity here: I needed to provide many more details to get this rolling. I think its something to do with the fact that its a connection that needs client authentication, and the hankshake needed more info to continue to the stage where the certificates were dumped.

Here is my working command:

openssl s_client -connect host:port -key our_private_key.pem -showcerts \
                 -cert our_server-signed_cert.pem

Hopefully this is a nudge in the right direction for anyone who could do with some more info.

While I agree with Ari's answer (and upvoted it :), I needed to do an extra step to get it to work with Java on Windows (where it needed to be deployed):

openssl s_client -showcerts -connect www.example.com:443 < /dev/null | openssl x509 -outform DER > derp.der

Before adding the openssl x509 -outform DER conversion, I was getting an error from keytool on Windows complaining about the certificate's format. Importing the .der file worked fine.

To get the certificate of remote server you can use openssl tool and you can find it between BEGIN CERTIFICATE and END CERTIFICATE which you need to copy and paste into your certificate file (CRT).

Here is the command demonstrating it:

ex +'/BEGIN CERTIFICATE/,/END CERTIFICATE/p' <(echo | openssl s_client -showcerts -connect example.com:443) -scq > file.crt

To return all certificates from the chain, just add g (global) like:

ex +'g/BEGIN CERTIFICATE/,/END CERTIFICATE/p' <(echo | openssl s_client -showcerts -connect example.com:443) -scq

Then you can simply import your certificate file (file.crt) into your keychain and make it trusted, so Java shouldn't complain.

On OS X you can double-click on the file or drag and drop in your Keychain Access, so it'll appear in login/Certificates. Then double-click on the imported certificated and make it Always Trust for SSL.

On CentOS 5 you can append them into /etc/pki/tls/certs/ca-bundle.crt file (and run: sudo update-ca-trust force-enable), or in CentOS 6 copy them into /etc/pki/ca-trust/source/anchors/ and run sudo update-ca-trust extract.

In Ubuntu, copy them into /usr/local/share/ca-certificates and run sudo update-ca-certificates.

The easiest command line for this, which includes the PEM output to add it to the keystore, as well as a human readable output and also supports SNI, which is important if you are working with an HTTP server is:

openssl s_client -servername example.com -connect example.com:443 \
    </dev/null 2>/dev/null | openssl x509 -text

The -servername option is to enable SNI support and the openssl x509 -text prints the certificate in human readable format.

For the benefit of others like me who tried to follow the good advice here when accessing AWS CloudFront but failed, the trick is to add -servername domain.name...

Source: https://serverfault.com/a/780450/8972

You can get and store the server root certificate using next bash script:

CERTS=$(echo -n | openssl s_client -connect $HOST_NAME:$PORT -showcerts | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p')
echo "$CERTS" | awk -v RS="-----BEGIN CERTIFICATE-----" 'NR > 1 { printf RS $0 > "'$SERVER_ROOT_CERTIFICATE'"; close("'$SERVER_ROOT_CERTIFICATE'") }'

Just overwrite required variables.

HOST=gmail-pop.l.google.com
PORT=995

openssl s_client -servername $HOST -connect $HOST:$PORT < /dev/null 2>/dev/null | openssl x509 -outform pem

to print only the certificate chain and not the server's certificate:

# MYHOST=myhost.com
# MYPORT=443
# openssl s_client -connect ${MYHOST}:${MYPORT} -showcerts 2>/dev/null </dev/null | awk '/^.*'"${MYHOST}"'/,/-----END CERTIFICATE-----/{next;}/-----BEGIN/,/-----END CERTIFICATE-----/{print}'

to update CA trust on CentOS/RHEL 6/7 :

# update-ca-trust enable
# openssl s_client -connect ${MYHOST}:${MYPORT} -showcerts 2>/dev/null </dev/null | awk '/^.*'"${MYHOST}"'/,/-----END CERTIFICATE-----/{next;}/-----BEGIN/,/-----END CERTIFICATE-----/{print}' >/etc/pki/ca-trust/source/anchors/myca.cert
# update-ca-trust extract

on CentOS/RHEL 5:

# openssl s_client -connect ${MYHOST}:${MYPORT} -showcerts 2>/dev/null </dev/null | awk '/^.*'"${MYHOST}"'/,/-----END CERTIFICATE-----/{next;}/-----BEGIN/,/-----END CERTIFICATE-----/{print}' >>/etc/pki/tls/certs/ca-bundle.crt

A one-liner to extract the certificate from a remote server in PEM format, this time using sed:

openssl s_client -connect www.google.com:443 2>/dev/null </dev/null |  sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p'

If your server is an email server (MS Exchange or Zimbra) maybe you need to add the starttls and smtp flags:

openssl s_client -starttls smtp -connect HOST_EMAIL:SECURE_PORT 2>/dev/null </dev/null | sed -ne '/-BEGIN CERTIFICATE-/,/-END CERTIFICATE-/p' > CERTIFICATE_NAME.pem

Where,

• HOST_EMAIL is the server domain, for example, mail-server.com.

• SECURE_PORT is the communication port, for example, 587 or 465

• CERTIFICATE_NAME output's filename (BASE 64/PEM Format)

Start the client:

openssl s_client -showcerts stackoverflow.com:443

Quit by stopping STDIN (CTRL+D), or terminate the process (CTRL+C).

To disable input and force the client to quit after displaying the certificates:

openssl s_client -showcerts stackoverflow.com:443 < /dev/null

I also had the same challenge and next to that I discovered that openssl doesn't return the root ca. I have built an alternative for specifically for this purpose which might be useful for other developers, see here: GitHub - Certificate ripper

Usage

• Printing to the console

crip print --url=https://stackoverflow.com/ --format=pem

• Exporting to a p12 trustore

crip export pkcs12 --url=https://stackoverflow.com/

The pkcs12 option can be replaced for pem or der if you want a different output.

There are already good answers. But it's worth to mention the latest curl version (>7.88.0) will do this simple for you...

curl https://example.com -w "%{certs}" -o /dev/null > cacert.pem

Add --insecure if the server uses self signed certificate. And add --head to avoid the response body.

See availability and requirements here: cURL -w certs feature

I was in case where two certificates was output from aboves commands; so i get to this point to extract only the 2nd part : the server certificate

Sorry for the long command:

openssl s_client -servername token.actions.githubusercontent.com -showcerts -connect token.actions.githubusercontent.com:443 2>/dev/null </dev/null | awk '/BEGIN CERTIFICATE/ && c++,/END CERTIFICATE/'