${APACHE_RUN_DIR} is not defined

From man apache2ctl:

ENVIRONMENT
 
The behaviour of apache2ctl can be influenced with these environment variables: APACHE_HTTPD, APACHE_LYNX, APACHE_STATUSURL, APACHE_ULIMIT_MAX_FILES, APACHE_RUN_DIR, APACHE_LOCK_DIR, APACHE_RUN_USER, APACHE_ARGUMENTS, APACHE_ENVVARS. See the comments in the script for details. These variables (except APACHE_ENVVARS) can be set in /etc/apache2/envvars.

A quick look at /etc/apache2/envvars shows the following:

# for supporting multiple apache2 instances
if [ "${APACHE_CONFDIR##/etc/apache2-}" != "${APACHE_CONFDIR}" ] ; then
    SUFFIX="-${APACHE_CONFDIR##/etc/apache2-}"
else
    SUFFIX=
fi

# Since there is no sane way to get the parsed apache2 config in scripts, some
# settings are defined via environment variables and then used in apache2ctl,
# /etc/init.d/apache2, /etc/logrotate.d/apache2, etc.
export APACHE_RUN_USER=www-data
export APACHE_RUN_GROUP=www-data
# temporary state file location. This might be changed to /run in Wheezy+1
export APACHE_PID_FILE=/var/run/apache2$SUFFIX/apache2.pid
export APACHE_RUN_DIR=/var/run/apache2$SUFFIX
export APACHE_LOCK_DIR=/var/lock/apache2$SUFFIX
# Only /var/log/apache2 is handled by /etc/logrotate.d/apache2.
export APACHE_LOG_DIR=/var/log/apache2$SUFFIX

-- sw