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:
# 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
Then:
sysctl --system
Older system:
sysctl -p /etc/sysctl.d/local.conf
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:
