mod_unique_id: unable to find IPv4 address

[Gary Fitts]

Installed MacPorts for the first time, then installed apache2. When I run sudo port load apache2, an httpd process starts up, and even responds to requests (to http://localhost) if I get them in fast enough. But then the process exits (whether or not it received any requests). The error log shows this:

[Fri Mar 20 11:40:41 2015] [warn] Init: Session Cache is not configured [hint: SSLSessionCache]
[Fri Mar 20 11:40:46 2015] [alert] (EAI 8)nodename nor servname provided, or not known: mod_unique_id: unable to find IPv4 address of "iMac.local"
Configuration Failed

I’ve searched the archives of this list and I see several references to similar problems, but no resolutions. Any help would be appreciated!

My computer:
iMac (27-inch, Mid 2010), 4 GB
OS X 10.10.2 Yosemite


FWIW, I added a ServerName directive to /opt/local/apache2/conf/httpd.conf:
#
# ServerName gives the name and port that the server uses to identify itself.
# This can often be determined automatically, but we recommend you specify
# it explicitly to prevent problems during startup.
#
# If your host doesn't have a registered DNS name, enter its IP address here.
#
#ServerName www.example.com:80
ServerName localhost:80


and my /etc/hosts file contains
##
# Host Database
#
# localhost is used to configure the loopback interface
# when the system is booting.  Do not change this entry.
##
127.0.0.1	localhost
255.255.255.255	broadcasthost
::1             localhost