incrontab

/var/www/site1/nginx.conf IN_MODIFY,IN_NO_LOOP /usr/local/sbin/nginx-reload.sh
/var/www/site2/nginx.conf IN_MODIFY,IN_NO_LOOP /usr/local/sbin/nginx-reload.sh
/var/www/site3/nginx.conf IN_MODIFY,IN_NO_LOOP /usr/local/sbin/nginx-reload.sh

nginx-reload-worker.sh

#!/bin/sh

error() {
    local RET=$1
    shift
    echo -e "$@" >&2
    exit "$RET"
}

sleep 5
service nginx reload || error 2 "nginx reload error"

nginx-reload.sh

#!/bin/sh

flock -x "/var/lock/nginx-reload" -c nginx-reload-worker.sh
logger -t "nginx-reload[$$]" "Reloading OK"