Comment # 14 on bug 929471 from Dennis Golden

When you configure the network with yast hostname and domain, it creates
/etc/hostname with the fqdn.

If you read the man page for hostname, it will tell you that:
  The  host  name  is  usually  set  once  at  system  startup  in   /etc/rc.d 
 /rc.inet1   or
       /etc/init.d/boot (normally by reading the contents of a file which
contains the host name,
       e.g.  /etc/hostname).

Obviously this is missing from systemd.

If you read the documentation for postfix, it obtains the value for my hostname
by doing a call get hostname which has not been set in the running kernel
because it has not done the above.

I have worked around the problem by putting this command:
  /bin/hostname -F /etc/hostname
in:
  /etc/boot.local

This should not be required.

I several machines with postfix custom main.cf and master.cf. I don't want to
hard code the myhostname variable, because I use the same configuration on
multiple machines.

This worked perfectly until systemd.

Regards,

Dennis