Performance Tuning with sysctl

Advanced15 min

Tune kernel parameters using sysctl to optimize network performance, file descriptor limits, and memory management.

Prerequisites

-Linux shell access
-Root or sudo access

Steps

View current kernel parameters

List all sysctl parameters and their current values.

$ sysctl -a 2>/dev/null | grep -E 'net.core.somaxconn|vm.swappiness|fs.file-max|net.ipv4.tcp_max_syn_backlog'

Check current file descriptor limits

View the maximum number of open file descriptors.

$ sysctl fs.file-max && ulimit -n

fs.file-max is the system-wide limit. ulimit -n is the per-process limit.

Optimize TCP settings for high-traffic servers

Increase TCP connection backlog and enable TCP optimizations.

$ sudo sysctl -w net.core.somaxconn=65535 && sudo sysctl -w net.ipv4.tcp_max_syn_backlog=65535

These changes are temporary and lost on reboot. Add them to /etc/sysctl.d/ to persist.

Adjust swappiness for server workloads

Reduce swappiness to prefer keeping application memory in RAM.

$ sudo sysctl -w vm.swappiness=10

Default is 60. For database servers, 10 is common. For desktops, 60 is fine.

Persist sysctl changes across reboots

Save tuning parameters to a config file so they survive reboots.

$ echo 'net.core.somaxconn=65535 vm.swappiness=10 fs.file-max=2097152' | sudo tee /etc/sysctl.d/99-performance.conf && sudo sysctl --system

Full Script

full-script.sh

#!/bin/bash
# Performance Tuning Audit
set -euo pipefail

echo "=== Current Performance Parameters ==="
echo "Swappiness:        $(sysctl -n vm.swappiness)"
echo "File max:          $(sysctl -n fs.file-max)"
echo "Somaxconn:         $(sysctl -n net.core.somaxconn)"
echo "TCP backlog:       $(sysctl -n net.ipv4.tcp_max_syn_backlog)"
echo "TCP keepalive:     $(sysctl -n net.ipv4.tcp_keepalive_time)s"
echo "Ulimit (soft):     $(ulimit -Sn)"
echo "Ulimit (hard):     $(ulimit -Hn)"

echo ""
echo "=== Memory ==="
echo "Total:    $(free -h | awk '/Mem:/{print $2}')"
echo "Used:     $(free -h | awk '/Mem:/{print $3}')"
echo "Cache:    $(free -h | awk '/Mem:/{print $6}')"
echo "Swap:     $(free -h | awk '/Swap:/{print $3}') used of $(free -h | awk '/Swap:/{print $2}')"

echo ""
echo "=== Recommended Server Tuning ==="
echo "sudo sysctl -w vm.swappiness=10"
echo "sudo sysctl -w net.core.somaxconn=65535"
echo "sudo sysctl -w fs.file-max=2097152"
echo "sudo sysctl -w net.ipv4.tcp_max_syn_backlog=65535"
echo ""
echo "Persist: Add to /etc/sysctl.d/99-performance.conf"

FAQ

Discussion

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#!/bin/bash # Performance Tuning Audit set -euo pipefail echo "=== Current Performance Parameters ===" echo "Swappiness: $(sysctl -n vm.swappiness)" echo "File max: $(sysctl -n fs.file-max)" echo "Somaxconn: $(sysctl -n net.core.somaxconn)" echo "TCP backlog: $(sysctl -n net.ipv4.tcp_max_syn_backlog)" echo "TCP keepalive: $(sysctl -n net.ipv4.tcp_keepalive_time)s" echo "Ulimit (soft): $(ulimit -Sn)" echo "Ulimit (hard): $(ulimit -Hn)" echo "" echo "=== Memory ===" echo "Total: $(free -h | awk '/Mem:/{print $2}')" echo "Used: $(free -h | awk '/Mem:/{print $3}')" echo "Cache: $(free -h | awk '/Mem:/{print $6}')" echo "Swap: $(free -h | awk '/Swap:/{print $3}') used of $(free -h | awk '/Swap:/{print $2}')" echo "" echo "=== Recommended Server Tuning ===" echo "sudo sysctl -w vm.swappiness=10" echo "sudo sysctl -w net.core.somaxconn=65535" echo "sudo sysctl -w fs.file-max=2097152" echo "sudo sysctl -w net.ipv4.tcp_max_syn_backlog=65535" echo "" echo "Persist: Add to /etc/sysctl.d/99-performance.conf"