Настраиваем лимиты на High-Loaded server.

etc/sysctl.conf:

net.core.somaxconn = 64000
net.ipv4.ip_local_port_range = 15000 61000
net.ipv4.tcp_fin_timeout = 30
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_tw_reuse = 1

/etc/security/limits.conf:

www-data - nofile 64000
root soft nofile 120000
root hard nofile 120000