found it.
it is missing from the Debian configuration
in /etc/default/jenkins
JENKINS_ENABLE_ACCESS_LOG="yes"
if [ "$JENKINS_ENABLE_ACCESS_LOG" = "yes" ]; then
PARAMS="$PARAMS --
accessLoggerClassName=winstone.accesslog.SimpleAccessLogger --
simpleAccessLogger.format=combined --simpleAccessLogger.file=/var/log/
jenkins/access"
fi
JENKINS_ARGS="--webroot=/var/cache/jenkins/war --httpPort=$HTTP_PORT --
ajp13Port=$AJP_PORT $PARAMS"