1. 系统日志
tail -f /var/log/messages
Apr 18 11:21:56 web5 kernel: possible SYN flooding on port 80. Sending cookies.
2.检查连接数 netstat -n | awk '/^tcp/ {++S[$NF]} END {for(a in S) print a, S[a]}'
TIME_WAIT 16855
CLOSE_WAIT 21
SYN_SENT 99
FIN_WAIT1 229
FIN_WAIT2 113
ESTABLISHED 8358
SYN_RECV 48965
CLOSING 3
LAST_ACK 313
正常 SYN_RECV 259
如果没有以上特征 业务流量好高
解决办法
net.ipv4.tcp_synack_retries = 0
net.ipv4.tcp_max_syn_backlog = 655350(注意该值要小于net.core.somaxconn)
net.core.somaxconn = 655350