centos有一个问题，例如有很多的tcp连接同时连接超出1024个连接数的时候，centos7 会出现一旦到1024则无法连接的情况，
即便你使用limit -n 1024 等这样的修改是无法其效果的，
以及各种修改可能都不起作用：
经过我们的大量研究最终解决了该问题
修改文件 vi /etc/sysctl.conf
如下：
vm.swappiness = 10
net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_fin_timeout = 30
net.ipv4.tcp_keepalive_time = 1200
net.ipv4.ip_local_port_range = 1024 65000
net.ipv4.tcp_max_tw_buckets = 5000
net.ipv4.tcp_mem = 786432 1048576 1572864
net.core.wmem_max = 873200
net.core.rmem_max = 873200
net.ipv4.tcp_wmem = 8192 436600 873200
net.ipv4.tcp_rmem = 32768 436600 873200
net.core.somaxconn = 256
net.core.netdev_max_backlog = 1000
net.ipv4.tcp_max_syn_backlog = 2048
net.ipv4.tcp_retries2 = 5
net.ipv4.tcp_keepalive_intvl = 30
net.ipv4.tcp_keepalive_probes = 3
net.ipv4.conf.lo.arp_ignore = 0
net.ipv4.conf.lo.arp_announce = 0
net.ipv4.conf.all.arp_ignore = 0
net.ipv4.conf.all.arp_announce = 0
net.ipv4.neigh.default.gc_thresh1 = 10240
net.ipv4.neigh.default.gc_thresh2 = 40960
net.ipv4.neigh.default.gc_thresh3 = 81920
fs.file-max = 655360
vm.max_map_count = 262144