Memcached is a software that implements a RAM caching service based on a hash table.

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    Memcached is a server that stores some data in RAM with a specified lifetime. The data is accessed by a key (name). You can think of Memcached as a hash table stored on the server. It's mostly used to cache web page code, database query results, etc.

    For starters, let's update the OS:

    # yum update
    

    After updating, perform a memcached installation:

    # yum install memcached
    

    Setting up memcached

    Let's edit the file:

    $ vim /etc/sysconfig/memcached
    

    Make sure that this configuration file has the following lines:

    PORT="11211"  
    USER="memcached"  
    MAXCONN="256"  
    CACHESIZE="64"  
    OPTIONS="-l 127.0.0.1"  
    
    • PORT 11211 is the default listening port for Memcached.

    • USER is the memcached user from which the daemon will run.

    • MAXCONN - the maximum number of possible connections.

    • CACHESIZE is the number of megabytes (64 MB) to use if you have a lot of traffic, this is good for most small/medium sites. For a busy server, you can increase it by 512 or 1 GB (1024 MB).

    • OPTIONS="-l 127.0.0.1‚Ä≥ - this means memcached will only listen on localhost, avoiding any external connections. It is set to INADDR_ANY by default

    Memcached is running:

    # systemctl enable memcached
    # systemctl start memcached
    

    Installing PHP extensions with memcached.

    execute:

    # yum install php-pear pecl_http php-devel
    

    And we execute:

    $ pecl install memcache
    

    If PECL asks you the question you see below when installing, just press ENTER:

    "Enable memcache session handler support? [yes]"
    

    Restarting services

    If your server has php-fpm installed, then to restart it, run:

    # service php-fpm reload
    

    If you have apache installed on your server, then to restart it, execute:

    # systemctl restart httpd
    

    Testing/checking Memcached

    Checking MemCache configuration

    Use the following command to test and verify that the Memcached service is working properly:

    $ echo "stats settings" | nc localhost 11211
    

    Now we need to check if the extension is enabled and make sure it works correctly. Create a file in your home directory and write the following PCP code:

    # echo "<?php phpinfo(); ?>" &gt; /var/www/html/php_info.php
    

    Configuring the firewall for Memcached

    Add the following rules to allow connections (for memcached to work):

    iptables -A INPUT -p tcp --destination-port 11211 -m state --state NEW -m iprange --src-range 192.168.1.10-192.168.1.15 -j ACCEPT  
    iptables -A INPUT -p udp --destination-port 11211 -m state --state NEW -m iprange --src-range 192.168.1.10-192.168.1.15 -j ACCEPT  
    

    Check if the memcached daemon is running on the OS:

    $ ps -aux | grep memcached