Optimizing Shadowsocks

If you see a lot of error: too many open files in your log, you should optimize your system. This tutorial applies to all shadowsocks servers (Python, libev, etc).

On Debian 7:

Create /etc/sysctl.d/local.conf with the following content:

fs.file-max = 51200

net.core.rmem_max = 67108864
net.core.wmem_max = 67108864
net.core.rmem_default = 65536
net.core.wmem_default = 65536
net.core.netdev_max_backlog = 4096
net.core.somaxconn = 4096

net.ipv4.tcp_syncookies = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_tw_recycle = 0
net.ipv4.tcp_fin_timeout = 30
net.ipv4.tcp_keepalive_time = 1200
net.ipv4.ip_local_port_range = 10000 65000
net.ipv4.tcp_max_syn_backlog = 4096
net.ipv4.tcp_max_tw_buckets = 5000
net.ipv4.tcp_fastopen = 3
net.ipv4.tcp_rmem = 4096 87380 67108864
net.ipv4.tcp_wmem = 4096 65536 67108864
net.ipv4.tcp_mtu_probing = 1
net.ipv4.tcp_congestion_control = hybla

Then:

sysctl --system

Warning: DO NOT ENABLE net.ipv4.tcp_tw_recycle!!! See this article.

If you use Supervisor, Make sure you have the following line in /etc/default/supervisor. Once you added that line, restart Supervisor (service stop supervisor && service start supervisor).

ulimit -n 51200

If you run shadowsocks in the background in other ways, make sure to add ulimit -n 51200 in your init script.

After optimizing, a busy Shadowsocks server that handles thousands of connections, takes about 30MB memory and 10% CPU. Notice that at the same time, Linux kernel usually uses >100MB RAM to hold buffer and cache for those connections. By using the sysctl config above, you are trading off RAM for speed. If you want to use less RAM, reduce the size of rmem and wmem.

Before & after: