Redis

Installation

Redis server is installed by default during the initial Centmin Mod LEMP stack installation via the REMI YUM repository. No manual steps are required for a fresh install.

Automatic Installation (Default)

The variable REDIS_SERVER_INSTALL='y' in centmin.sh ensures Redis is installed automatically. The REMI repository provides Redis 7.2 as a module stream on EL8+ systems.

Manual Installation via Addon Script

If Redis was not installed during initial setup, use the addon script:

/usr/local/src/centminmod/addons/redis-server-install.sh install

Upgrading Redis

To upgrade Redis from an older REMI module stream (e.g., 6.2 to 7.2) on EL8+:

/usr/local/src/centminmod/addons/redis-server-install.sh upgrade

Source Compile Option

For a source-compiled Redis 6.2.6 installation (instead of REMI RPM):

/usr/local/src/centminmod/addons/redis-server-install.sh install-source

PHP Redis Extension

The phpredis PHP extension provides a PHP API for communicating with the Redis server. Install or reinstall it via centmin.sh Menu Option 13.

Menu Option 13 Submenu

phpredis Version by PHP Version

Compression Support

The phpredis extension is compiled with support for multiple compression algorithms:

• zstd — Zstandard compression for efficient data storage
• LZ4 — Fast lossless compression
• LZF — Lightweight LZF compression

igbinary Serialization

The igbinary binary serializer is enabled for phpredis on PHP 7.x to reduce serialized data size. It is disabled on PHP 8.0+ due to known segfault risks with certain workloads.

Configuration

Redis server configuration is managed through configuration files and systemd service settings.

Configuration Files

I/O Threads Auto-Scaling

Centmin Mod automatically configures Redis I/O threads based on CPU count:

System Tweaks

The Redis installer applies system optimizations:

• vm.overcommit_memory=1 — Allows background saves without memory allocation failures
• Transparent Huge Pages (THP) disabled — Prevents latency spikes during forking
• Systemd LimitNOFILE=524288 — High file descriptor limit for busy servers

Service Management

# EL8/EL9/EL10 (systemd)
systemctl start redis
systemctl stop redis
systemctl restart redis
systemctl status redis

# CentOS 7 (EOL)
service redis start
service redis stop
service redis restart

Nginx Redis Integration

Centmin Mod compiles Nginx with several Redis-related modules for direct Redis integration at the web server level:

The ngx_http_redis module (0.4.0-cmm) is a Centmin Mod maintained fork that allows Nginx to query Redis directly for cached content, bypassing PHP entirely for cached pages.

Usage Examples

PHP Caching Example

<?php
$redis = new Redis();
$redis->connect('127.0.0.1', 6379);

// Store a value with 300-second TTL
$redis->setex('mykey', 300, 'cached_value');

// Retrieve the value
$value = $redis->get('mykey');
echo $value; // outputs: cached_value
?>

PHP Session Storage

Configure PHP to use Redis for session storage by adding to your php.ini or /etc/centminmod/php.d/ scan directory:

session.save_handler = redis
session.save_path = "tcp://127.0.0.1:6379"

WordPress Object Cache

For WordPress sites, Redis can be used as a persistent object cache via plugins like Redis Object Cache or Object Cache Pro. These plugins store WordPress transients, options, and database query results in Redis for faster page loads.

Monitoring

Use redis-cli to monitor Redis server status and performance:

# Full server info
redis-cli INFO

# Memory usage
redis-cli INFO memory

# Connected clients and stats
redis-cli INFO clients

# Real-time command monitoring (Ctrl+C to stop)
redis-cli MONITOR

# Key statistics
redis-cli INFO keyspace

# Latency check
redis-cli --latency