Kernel Parameter Tuning with sysctl

What is sysctl?

sysctl allows you to view and modify kernel parameters at runtime. These parameters control networking, memory management, filesystem behavior, and security features.

View Parameters

# Show all
sysctl -a

# Show specific
sysctl net.ipv4.ip_forward
sysctl vm.swappiness

Modify at Runtime

# Temporary (lost on reboot)
sudo sysctl -w net.ipv4.ip_forward=1
sudo sysctl -w vm.swappiness=10

Make Permanent

Create /etc/sysctl.d/99-custom.conf:

# Network performance
net.core.somaxconn = 65535
net.ipv4.tcp_fastopen = 3
net.ipv4.tcp_tw_reuse = 1

# Memory
vm.swappiness = 10
vm.dirty_ratio = 40
vm.dirty_background_ratio = 10

# Security
net.ipv4.conf.all.rp_filter = 1
net.ipv4.icmp_echo_ignore_broadcasts = 1
kernel.randomize_va_space = 2

# File handles
fs.file-max = 2097152
fs.inotify.max_user_watches = 524288

sudo sysctl -p /etc/sysctl.d/99-custom.conf

Common Tuning Categories

• Web servers — increase connection limits and TCP buffers
• Database servers — tune dirty page ratios and swappiness
• Security — enable SYN cookies, disable source routing