source: server-ip-memory-usage/trunk/server-ip-memory-usage.php

<?php
/*
Plugin Name: Server IP & Memory Usage Display
Plugin URI: http://apasionados.es/#utm_source=wpadmin&utm_medium=plugin&utm_campaign=server-ip-memory-usage-plugin
Description: Show the memory limit, current memory usage and IP address in the admin footer.
Version: 2.2.0
Author: Apasionados, Apasionados del Marketing
Author URI: http://apasionados.es
Text Domain: server-ip-memory-usage
Domain Path: /lang
*/

if ( is_admin() ) {

        class IP_Address_Memory_Usage {

                private $memory = array();

                public function __construct() {
                        // Cargar traducciones a partir de init (o plugins_loaded)
                        add_action( 'init', array( $this, 'load_textdomain' ) );

                        add_action( 'init', array( $this, 'check_limit' ) );
                        add_filter( 'admin_footer_text', array( $this, 'add_footer' ) );
                }

                public function load_textdomain() {
                        load_plugin_textdomain(
                                'server-ip-memory-usage',
                                false,
                                dirname( plugin_basename( __FILE__ ) ) . '/lang/'
                        );
                }

                public function check_limit() {
                        $this->memory['limit'] = (int) ini_get( 'memory_limit' );
                }

                private function check_memory_usage() {
                        $this->memory['usage'] = function_exists( 'memory_get_peak_usage' )
                                ? round( memory_get_peak_usage( true ) / 1024 / 1024, 2 )
                                : 0;

                        if ( ! empty( $this->memory['usage'] ) && ! empty( $this->memory['limit'] ) ) {
                                $this->memory['percent'] = round( $this->memory['usage'] / $this->memory['limit'] * 100, 0 );
                                $this->memory['color']   = 'font-weight:normal;';

                                if ( $this->memory['percent'] > 75 ) {
                                        $this->memory['color'] = 'font-weight:bold;color:#E66F00';
                                }
                                if ( $this->memory['percent'] > 90 ) {
                                        $this->memory['color'] = 'font-weight:bold;color:red';
                                }
                        }
                }

                private function format_wp_limit( $size ) {
                        $value  = substr( $size, -1 );
                        $return = substr( $size, 0, -1 );

                        $return = (int) $return;

                        switch ( strtoupper( $value ) ) {
                                case 'P':
                                        $return *= 1024;
                                case 'T':
                                        $return *= 1024;
                                case 'G':
                                        $return *= 1024;
                                case 'M':
                                        $return *= 1024;
                                case 'K':
                                        $return *= 1024;
                        }

                        return $return;
                }

                private function check_wp_limit() {
                        $memory = $this->format_wp_limit( WP_MEMORY_LIMIT );
                        $memory = size_format( $memory );

                        return ( $memory ) ? $memory : __( 'N/A', 'server-ip-memory-usage' );
                }

                public function add_footer( $content ) {
                        $this->check_memory_usage();

                        $server_ip_address = ! empty( $_SERVER['SERVER_ADDR'] ) ? $_SERVER['SERVER_ADDR'] : '';
                        if ( $server_ip_address === '' ) {
                                $server_ip_address = ! empty( $_SERVER['LOCAL_ADDR'] ) ? $_SERVER['LOCAL_ADDR'] : '';
                        }

                        $content .= ' | ' . __( 'Memory', 'server-ip-memory-usage' ) . ': ' . $this->memory['usage'] . ' ' .
                                __( 'of', 'server-ip-memory-usage' ) . ' ' . $this->memory['limit'] .
                                ' MB (<span style="' . $this->memory['color'] . '">' . $this->memory['percent'] .
                                '%</span>) | ' . __( 'WP LIMIT', 'server-ip-memory-usage' ) . ': ' . $this->check_wp_limit() .
                                ' | IP ' . $server_ip_address . ' (' . gethostname() . ') | PHP ' . PHP_VERSION .
                                ' @' . ( PHP_INT_SIZE * 8 ) . 'BitOS';

                        return $content;
                }
        }

        add_action( 'plugins_loaded', function () {
                new IP_Address_Memory_Usage();
        } );
}

/**
 * Check on plugin activation
 */
function server_ip_memory_usage_activation() {
        if ( version_compare( PHP_VERSION, '5.3', '<' ) ) {
                deactivate_plugins( plugin_basename( __FILE__ ) );

                $plugin_data    = get_plugin_data( __FILE__ );
                $plugin_version = $plugin_data['Version'];
                $plugin_name    = $plugin_data['Name'];

                wp_die(
                        '<h1>Could not activate plugin: PHP version error</h1>' .
                        '<h2>PLUGIN: <i>' . esc_html( $plugin_name . ' ' . $plugin_version ) . '</i></h2>' .
                        '<p><strong>You are using PHP version ' . esc_html( PHP_VERSION ) . '</strong>. ' .
                        'This plugin has been tested with PHP versions 5.3 and greater.</p>' .
                        '<p>WordPress itself recommends using PHP version 7 or greater. Please upgrade your PHP version or contact your Server administrator.</p>',
                        'Could not activate plugin: PHP version error',
                        array( 'back_link' => true )
                );
        }
}
register_activation_hook( __FILE__, 'server_ip_memory_usage_activation' );