1 Fast TCP开启

如果双端都支持FastTCP，那么可以通过开启FastTCP来降低延时。服务端设置方法有两种，要门在config.json中添加fast_open为true，要么在执行ssserver带上--fast-open。然后在命令行中运行

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echo 3 > /proc/sys/net/ipv4/tcp_fastopen

2 进一步优化

这个优化方法适合所有的shadowsocks版本，具体方法如下。创建文件/etc/sysctl.d/local.conf，并在文件中添加如下内容：

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# max open files
fs.file-max = 51200
# max read buffer
net.core.rmem_max = 67108864
# max write buffer
net.core.wmem_max = 67108864
# default read buffer
net.core.rmem_default = 65536
# default write buffer
net.core.wmem_default = 65536
# max processor input queue
net.core.netdev_max_backlog = 4096
# max backlog
net.core.somaxconn = 4096

# resist SYN flood attacks
net.ipv4.tcp_syncookies = 1
# reuse timewait sockets when safe
net.ipv4.tcp_tw_reuse = 1
# turn off fast timewait sockets recycling
net.ipv4.tcp_tw_recycle = 0
# short FIN timeout
net.ipv4.tcp_fin_timeout = 30
# short keepalive time
net.ipv4.tcp_keepalive_time = 1200
# outbound port range
net.ipv4.ip_local_port_range = 10000 65000
# max SYN backlog
net.ipv4.tcp_max_syn_backlog = 4096
# max timewait sockets held by system simultaneously
net.ipv4.tcp_max_tw_buckets = 5000
# turn on TCP Fast Open on both client and server side
net.ipv4.tcp_fastopen = 3
# TCP receive buffer
net.ipv4.tcp_rmem = 4096 87380 67108864
# TCP write buffer
net.ipv4.tcp_wmem = 4096 65536 67108864
# turn on path MTU discovery
net.ipv4.tcp_mtu_probing = 1

# for high-latency network
net.ipv4.tcp_congestion_control = hybla

# for low-latency network, use cubic instead
# net.ipv4.tcp_congestion_control = cubic

然后运行

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sysctl --system

应用上述设置。最后在启动脚本中，于ssserver前添加

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ulimit -n 51200

这个设置方法，会消耗比较多的内存，但是会换来速度的大幅上升。