Commands aren't always processed and the the error is displayed

fdpi_ctrl uses ordinary linux stack to communicat with the dpi, so the tuning recommendations is similar to the high load web servers (nginx-like)

Settings are similar to the nginx. It is recommended to insert it /etc/sysctl.conf (to keep safe from being droped after server restart)

# Operating system network stack optimization
net.core.netdev_max_backlog=10000
net.core.somaxconn=262144
net.ipv4.tcp_syncookies=1
net.ipv4.tcp_max_syn_backlog = 262144
net.ipv4.tcp_max_tw_buckets = 720000
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_fin_timeout = 30
net.ipv4.tcp_keepalive_time = 1800
net.ipv4.tcp_keepalive_probes = 7
net.ipv4.tcp_keepalive_intvl = 30
net.core.wmem_max = 33554432
net.core.rmem_max = 33554432
net.core.rmem_default = 8388608
net.core.wmem_default = 4194394
net.ipv4.tcp_rmem = 4096 8388608 16777216
net.ipv4.tcp_wmem = 4096 4194394 16777216

for 1Gb interface:

net.core.netdev_max_backlog=10000

for 10Gb interface:

net.core.netdev_max_backlog=30000

To avoid rebooting the server they can be modified on-the-fly by applying the command: sysctl -w настройка, например, sysctl -w net.ipv4.tcp_tw_reuse=1

This should do the trick

For the CentOS 7.*
example:

# Operating system network stack optimization
net.core.netdev_max_backlog=65536
net.core.optmem_max=25165824
net.core.somaxconn=1024
net.ipv4.tcp_max_orphans = 60000
net.ipv4.tcp_no_metrics_save = 1
net.ipv4.tcp_window_scaling = 1
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_sack = 1
net.ipv4.tcp_syncookies=1
net.ipv4.tcp_max_syn_backlog = 262144
net.ipv4.tcp_max_tw_buckets = 720000
net.ipv4.tcp_tw_recycle = 1
net.ipv4.tcp_timestamps = 1
net.ipv4.tcp_tw_reuse = 1
net.ipv4.tcp_fin_timeout = 30
net.ipv4.tcp_keepalive_time = 1800
net.ipv4.tcp_keepalive_probes = 7
net.ipv4.tcp_keepalive_intvl = 30
net.core.wmem_max = 33554432
net.core.rmem_max = 33554432
net.core.rmem_default = 8388608
net.core.wmem_default = 4194394
net.ipv4.tcp_rmem = 4096 8388608 16777216
net.ipv4.tcp_wmem = 4096 4194394 16777216

update command:

sysctl –system

Supplementary information CentOS7