I have a SSL CRT file in PEM format. Is there a way that I can extract the common name (CN) from the certificate from the command line?

  • 3
    Note, however, that in multi-domain certificates, CN does not contain all of them. – Torsten Bronger Feb 8 '17 at 5:27

If you have openssl installed you can run:

openssl x509 -noout -subject -in server.pem
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    You can extract the CN out of the subject with: openssl x509 -noout -subject -in server.pem | sed -n '/^subject/s/^.*CN=//p' – Matthew Buckett Dec 4 '14 at 12:09
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    I modified what @MatthewBuckett said and used sed -e 's/^subject.*CN=\([a-zA-Z0-9\.\-]*\).*$/\1/' to get just the domain as I had additional details after the CN. Its not super strict matching for a valid CN but in most cases it works, you could be more slack and replace [a-zA-Z0-9\.\-] with [^/] but I am not certain that would always work. – flungo Jun 4 '15 at 16:11
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    Add \* to what @flungo used to support wildcard domains: sed -e 's/^subject.*CN=\([a-zA-Z0-9\.\-\*]*\).*$/\1/' ([^/] works in my case, though) – bryn Sep 12 '15 at 23:18
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    The sed commands suggested above won't work if the cert has Relative Distinguished Names (RDNs) specified after the Common Name (CN), for example OU (OrganizationalUnit) or C (Country). One way to cater for such cases would be an additional sed: openssl x509 -noout -subject -in server.pem | sed 's/^.*CN=//' | sed sed 's/\/.*$//'. – Ohad Schneider Jan 12 '17 at 15:45
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    Easier way to separate CN from other RDN/ATVs in Subject name: openssl x509 -noout -subject -nameopt multiline | grep commonName or for the value only | sed -n 's/ *commonName *= //p' – dave_thompson_085 Mar 22 '17 at 17:03
certtool -i < whatever.pem | egrep "^\s+Subject:"

Notice that's directing the file to standard input via <, not using it as argument. Sans egrep this will print the whole certificate out, but the CN is in the Subject: field near the top (beware there's also a CN value in the Issuer: field).

X.509 Certificate Information:
    Version: 3
    Serial Number (hex): 01
    Issuer: [...] CN=unixandlinux.ex  <- Not this one.
    Validity: ...
    Subject: CN=goldilocks

certtool is part of gnutls, if it is not installed just search for that. GnuTLS is a little nicer than OpenSSL, IMO.

  • 2
    Good answer, +1. For Mac OS X, I had to use gnutls-certtool which was installed via brew install gnutls – Mike D Jan 16 '18 at 16:57

I found the above answer, and found it to be very useful, but I also found that the certtool command syntax (on Ubuntu Linux, today) was noticeably different than described by goldilocks, as was the output. So, I thought it best to update that excellent answer with what might be "today's version."

The "i" option (now?) stands for "import," according to man certtool, so the proper command appears to be "d", "display." So, this command:

certtool d myfoo.crt

(The file-extension in my case just happens to be .crt not .pem ... this is not relevant.)

... produces output that, in relevant part, looks like this:

Common Name     : Foobar

Unquestionably, goldilocks was right: certtool output is much easier easier to work with than openssl in this case.

  • 1
    I suspect we are talking about completely different pieces of software. I have never seen a version of certtool that took options sans the usual operators (- or --), and man certtool for v. 3.5.8 (debian), 3.5.16 (fedora, the only version after that in the upstream stable branch is 3.5.17 from a month ago), GnuTLS's online documentation and, indeed, the online man page for Ubuntu 17.10 (same version as current debian) all refer to: – goldilocks Jan 17 '18 at 12:30
  • "-i, --certificate-info: Print information on the given certificate," whereas "-d" is "--debug". Very strange. O_o? – goldilocks Jan 17 '18 at 12:31

I used: openssl x509 -noout -subject -in mycert.crt | awk -F= '{print $NF}' add | sed -e 's/^[ \t]*//' If you can't live with the white space

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