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I'm following this guide

https://www.linuxtechi.com/configure-domainkeys-with-postfix-on-centos-7/

When I get to this section, it gives an error

# opendkim-default-keygen
Generating default DKIM keys:
Cannot determine host's domain name, so skipping default key generation.

I do have my hostname set

# hostname
domain.org

# cat /etc/hostname
domain.org

# cat /etc/hosts
# Your system has configured 'manage_etc_hosts' as True.
# As a result, if you wish for changes to this file to persist
# then you will need to either
# a.) make changes to the master file in /etc/cloud/templates/hosts.redhat.tmpl
# b.) change or remove the value of 'manage_etc_hosts' in
#     /etc/cloud/cloud.cfg or cloud-config from user-data
#
# The following lines are desirable for IPv4 capable hosts
127.0.0.1 domain domain.org
127.0.0.1 localhost.localdomain localhost
127.0.0.1 localhost4.localdomain4 localhost4

# The following lines are desirable for IPv6 capable hosts
::1 domain domain.org
::1 localhost.localdomain localhost
::1 localhost6.localdomain6 localhost6

# cat /etc/sysconfig/network
NETWORKING=yes
HOSTNAME=domain.org
NOZEROCONF=yes

(I replaced all instances of the domain name with domain.)

Other pages on the web only say to set the hostname, which is set.

# cat /etc/centos-release
CentOS Linux release 7.5.1804 (Core)
Chloe
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  • Usually I use the [opendkim-genkey](http://www.opendkim.org/opendkim-genkey.8.html) program. I don't even have the `opendkim-default-keygen` program on my servers... although I run Debian, so perhaps the installed base is different. `opendkim-genkey` allows the domain to be specified with the `-d` option. – RubberStamp Jan 19 '19 at 20:52

1 Answers1

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Thanks to RubberStamp's comment, I just viewed the opendkim-default-keygen file and copied & pasted each line manually in another window.

# less /usr/sbin/opendkim-default-keygen

[root@domain postfix]# prog=opendkim
[root@domain postfix]# KEYGEN=/usr/sbin/$prog-genkey
[root@domain postfix]# DKIM_SELECTOR=default
[root@domain postfix]# DKIM_KEYDIR=/etc/$prog/keys
[root@domain postfix]# ls /etc/opendkim
keys  KeyTable  SigningTable  TrustedHosts
[root@domain postfix]# ls /etc/opendkim/keys
[root@domain postfix]# hostname --domain
[root@domain postfix]# mkdir -p $DKIM_KEYDIR
[root@domain postfix]# $KEYGEN -D $DKIM_KEYDIR -s $DKIM_SELECTOR -d domain.org
[root@domain postfix]# chown -R root:$prog $DKIM_KEYDIR
[root@domain postfix]# chmod 640 $DKIM_KEYDIR/$DKIM_SELECTOR.private
[root@domain postfix]# chmod 644 $DKIM_KEYDIR/$DKIM_SELECTOR.txt
Chloe
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  • So, it looks like `opendkim-default-keygen` is a script which sets the options for `opendkim-genkey` .... Were you able to generate your key and correctly place it as a DNS TXT entry? .... If so, it's probably a good idea to check the record using [Dmarcian DKIM Inspector](https://dmarcian.com/dkim-inspector/) – RubberStamp Jan 21 '19 at 20:49