https://www.hivelocity.net/kb/how-to-check-if-your-linux-server-is-under-ddos-attack-2/
Xem số lượng CPU
# grep processor /proc/cpuinfo | wc -l
Xem thời gian hoạt động
# uptime

kiểm tra các kết nối
# netstat -ntu|awk '{print $5}'|cut -d: -f1 -s|sort|uniq -c|sort -nk1 -r

To find IPs from the same /16 (xxx.xxx.0.0) subnet, use:
# netstat -ntu|awk '{print $5}'|cut -d: -f1 -s |cut -f1,2 -d'.'|sed 's/$/.0.0/'|sort|uniq -c|sort -nk1 -r

To find IPs from the same /24 (xxx.xxx.xxx.0) subnet, use:
# netstat -ntu|awk '{print $5}'|cut -d: -f1 -s |cut -f1,2,3 -d'.'|sed 's/$/.0/'|sort|uniq -c|sort -nk1 -r