Linux sysctl Guide

Complete beginner-friendly guide to sysctl on Linux, covering Arch Linux, CachyOS, and other distributions including kernel parameters, system tuning, and performance optimization.

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Table of Contents

1. Understanding sysctl
2. Viewing Parameters
3. Setting Parameters
4. Common Parameters
5. Performance Tuning
6. Troubleshooting

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Understanding sysctl

What is sysctl?

sysctl configures kernel parameters at runtime.

Uses:

• Network tuning: Optimize network performance
• Memory management: Configure memory settings
• Security: Harden system settings
• Performance: Optimize system performance

Why it matters:

• Runtime changes: Modify settings without reboot
• System optimization: Tune for your needs
• Troubleshooting: Fix system issues

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Viewing Parameters

List All Parameters

View parameters:

# List all parameters
sysctl -a

# List specific category
sysctl -a | grep net

# View single parameter
sysctl kernel.hostname

Common Categories

Parameter categories:

# Network parameters
sysctl -a | grep net

# Kernel parameters
sysctl -a | grep kernel

# Virtual memory
sysctl -a | grep vm

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Setting Parameters

Temporary Changes

Set temporarily:

# Set parameter
sudo sysctl kernel.hostname=myhost

# Set network parameter
sudo sysctl net.ipv4.ip_forward=1

Note: Changes are lost after reboot.

Permanent Changes

Make permanent:

# Edit sysctl config
sudo vim /etc/sysctl.conf

Add:

# Network forwarding
net.ipv4.ip_forward = 1

# Kernel hostname
kernel.hostname = myhost

Apply:

# Apply changes
sudo sysctl -p

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Common Parameters

Network Parameters

Network settings:

# Enable IP forwarding
net.ipv4.ip_forward = 1

# Disable ICMP redirects
net.ipv4.conf.all.accept_redirects = 0

# TCP keepalive
net.ipv4.tcp_keepalive_time = 600

Memory Parameters

Memory settings:

# Swappiness (0-100)
vm.swappiness = 10

# Overcommit memory
vm.overcommit_memory = 1

Security Parameters

Security settings:

# Disable IP source routing
net.ipv4.conf.all.accept_source_route = 0

# Enable SYN cookies
net.ipv4.tcp_syncookies = 1

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Performance Tuning

Network Performance

Optimize network:

# Increase TCP buffer sizes
net.core.rmem_max = 16777216
net.core.wmem_max = 16777216
net.ipv4.tcp_rmem = 4096 87380 16777216
net.ipv4.tcp_wmem = 4096 65536 16777216

File System Performance

Optimize filesystem:

# Increase file handles
fs.file-max = 2097152

# Inotify limits
fs.inotify.max_user_watches = 524288

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Troubleshooting

Parameter Not Applied

Check configuration:

# Verify parameter
sysctl parameter-name

# Check config file
cat /etc/sysctl.conf

# Apply manually
sudo sysctl -p

Invalid Parameter

Test parameter:

# Test before applying
sudo sysctl -w parameter=value

# Check if valid
sysctl parameter-name

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Summary

This guide covered sysctl usage, parameter configuration, and system tuning for Arch Linux, CachyOS, and other distributions.

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Next Steps

• Performance Tuning - System optimization
• System Configuration - System setup
• Networking - Network configuration
• sysctl Documentation: man sysctl

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This guide covers Arch Linux, CachyOS, and other Linux distributions. For distribution-specific details, refer to your distribution's documentation.