How to install Memcached on CentOS 6

Memcached is a high-performance, distributed memory object caching server, generic in nature, but intended for use in speeding up dynamic web applications by alleviating database load. You need to install the following packages:

• memcached : High Performance, Distributed Memory Object Cache server package.
• perl-Cache-Memcached : Perl client (library) to work with memcached server.
• python-memcached : Perl client (library) to work with memcached server.
• php-pecl-memcache : PHP extension to work with the Memcached server.

Memcached is used by many high traffic sites including YouTube, Reddit, Facebook, Twitter, and many others.Google App Engine, AppScale and Amazon Web Services also offer a memcached service through an API. Memcached is also supported by popular open source projects and CMSs such as Drupal, Joomla, WordPress, and many more. WARNING! These examples only works with RHEL / CentOS Linux version 6.x or above.

Task: Install memcached

Open a terminal or login to remote server using ssh client. Type the following yum command to install the same:

yum install memcached.x86_64 php-pecl-memcache.x86_64

Sample outputs:

Loaded plugins: product-id, rhnplugin, subscription-manager Updating certificate-based repositories. Setting up Install Process Resolving Dependencies --> Running transaction check ---> Package memcached.x86_64 0:1.4.4-3.el6 will be installed --> Processing Dependency: libevent-1.4.so.2()(64bit) for package: memcached-1.4.4-3.el6.x86_64 ---> Package php-pecl-memcache.x86_64 0:3.0.5-3.el6 will be installed --> Processing Dependency: /usr/bin/pecl for package: php-pecl-memcache-3.0.5-3.el6.x86_64 --> Processing Dependency: /usr/bin/pecl for package: php-pecl-memcache-3.0.5-3.el6.x86_64 --> Running transaction check ---> Package libevent.x86_64 0:1.4.13-1.el6 will be installed ---> Package php-pear.noarch 1:1.9.4-4.el6 will be installed --> Finished Dependency Resolution Dependencies Resolved Package Arch Version Repository Size

Installing: memcached x86_64 1.4.4-3.el6 rhel-x86_64-server-6 68 k php-pecl-memcache x86_64 3.0.5-3.el6 rhel-x86_64-server-6 60 k Installing for dependencies: libevent x86_64 1.4.13-1.el6 rhel-x86_64-server-6 66 k php-pear noarch 1:1.9.4-4.el6 rhel-x86_64-server-6 393 k Transaction Summary

Install 4 Package(s) Total download size: 587 k Installed size: 0 Is this ok y/Nownloading Packages: (1/4): libevent-1.4.13-1.el6.x86_64.rpm | 66 kB 00:00 (2/4): memcached-1.4.4-3.el6.x86_64.rpm | 68 kB 00:00 (3/4): php-pear-1.9.4-4.el6.noarch.rpm | 393 kB 00:00 (4/4): php-pecl-memcache-3.0.5-3.el6.x86_64.rpm | 60 kB 00:00

Total 2.4 MB/s | 587 kB 00:00 Running rpm_check_debug Running Transaction Test Transaction Test Succeeded Running Transaction Warning: RPMDB altered outside of yum. Installing : 1:php-pear-1.9.4-4.el6.noarch 1/4 Installing : libevent-1.4.13-1.el6.x86_64 2/4 Installing : memcached-1.4.4-3.el6.x86_64 3/4 Installing : php-pecl-memcache-3.0.5-3.el6.x86_64 4/4 Installed products updated. Installed: memcached.x86_64 0:1.4.4-3.el6 php-pecl-memcache.x86_64 0:3.0.5-3.el6 Dependency Installed: libevent.x86_64 0:1.4.13-1.el6 php-pear.noarch 1:1.9.4-4.el6 Complete!

How Do I Configure Memcached Server?

Edit /etc/sysconfig/memcached file, enter:

vi /etc/sysconfig/memcached

Sample outputs:

PORT="11211" USER="memcached" MAXCONN="1024" CACHESIZE="64" OPTIONS="

For busy servers you need to increase the values as follows: MAXCONN: Use 1024 max simultaneous connections; the default is 1024. For busy server increase this number as per requirements. CACHESIZE: Use 64 MB memory max to use for object storage; the default is 64 megabytes. For busy server you can set it to 512MB or 1GB (1024). >OPTIONS: You can set server IP address (listen on address) here so that apache/php/nginx based serer can connect to the server. By default it is set to INADDR_ANY. This is an important option to consider as there is no other way to secure the installation. Binding to an internal or firewalled network interface is suggested. Here is my sample update file:

PORT="11211" USER="memcached" MAXCONN="4096" CACHESIZE="512" OPTIONS="-l 192.168.1.15"

How Do I Start / Stop / Restart Memcached Server?

Type the following commands:

/etc/init.d/memcached start
/etc/init.d/memcached stop
/etc/init.d/memcached restart
/etc/init.d/memcached status

OR run a System V init script using service command

/sbin/service memcached start
/sbin/service memcached stop
/sbin/service memcached restart
/sbin/service memcached status

How do I start Memcached automatically after a reboot

chkconfig memcached on

How Do I Verify That Memcached is Running and Working?

Type the following command to see if it is running or not:

pgrep memcached
netstat -tulpn | grep :11211

Sample outputs:

tcp 0 0 192.168.1.15:11211 0.0.0.0: LISTEN 24964/memcached udp 0 0 192.168.1.15:11211 0.0.0.0: 24964/memcached

Use the memcached-tool to get general stats:

memcached-tool 192.168.1.15:11211 stats

Sample outputs:

192.168.1.15:11211 Field Value

 accepting_conns           1
       auth_cmds           0
     auth_errors           0
           bytes     5481902
      bytes_read     8242409
   bytes_written    26023492
      cas_badval           0
        cas_hits           0
      cas_misses           0
       cmd_flush           0
         cmd_get        9042
         cmd_set        4469
     conn_yields           0

connection_structures 48

curr_connections          47
      curr_items        3197
       decr_hits           0
     decr_misses           0
     delete_hits           6
   delete_misses         112
       evictions           0
        get_hits        7490
      get_misses        1552
       incr_hits           0
     incr_misses           0
  limit_maxbytes   536870912
listen_disabled_num        0
             pid       24964
    pointer_size          64
   rusage_system    0.149977
     rusage_user    0.043993
         threads           4
            time  1327395688
total_connections        171
     total_items        3226
          uptime         198
         version       1.4.4

How Do I Configure Firewall To Protect My Memcached Server?

Make sure iptables only allows access to your own servers. Edit /etc/sysconfig/iptables and append the following rules or add it as follows to your shell scripts: add to your shell script assumption default INPUT policy is set to DROP only accept connection to tcp/udp port 11211 if ip is between 192.168.1.10 and 192.168.1.15

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.