memcached is a high-performance memory object caching system intended to speed up dynamic web applications by alleviating database load.

memcached is meant to work in concert with something like the MySQL query cache, not replace it. The two implementations excel at vastly different things: memcached is an object cache, while MySQL provides a query cache.

memcached is extremely fast. It uses libevent, which provides a mechanism to execute a callback function when a specific event occurs on a file descriptor, to scale to any number of open connections. On a modern Linux system memcached utilizes epoll, is completely non-blocking for network I/O, ensures memory never gets fragmented, and uses its own slab allocator and hash table to achieve 0(1) virtual memory allocation.

How it install it on Linux server ?

• Install dependency software (Libevent)

#curl -O http://monkey.org/~provos/libevent-1.4.9-stable.tar.gz
#tar -xzvf libevent-1.4.9-stable.tar.gz
#cd libevent*
#./configure
#make
#make install

• Now let’s download the newest Memcached source

#curl -O http://www.danga.com/memcached/dist/memcached-1.3.0.tar.gz
#tar zxf memcached-1.3.0.tar.gz
#cd memcached-1.3.0
#./configure
#make
#make install

• Then add /usr/local/lib to LD_LIBRARY_PATH in your .bash_profile

LD_LIBRARY_PATH=$LD_LIBRARY_PATH:/usr/local/lib
export LD_LIBRARY_PATH

How it Works

First, you start up the memcached daemon on as many spare machines as you have. The daemon has no configuration file, just a few command line options, only 3 or 4 of which you’ll likely use:

Run Memcached as a daemon (d = daemon, m = memory, u = user, l = IP to listen to, p = port)

#memcached -d -m 1024 -u root -l 127.0.0.1 -p 11211 –u nobody

This starts memcached as a daemon (-d) on the IP address and port specified with -l and -p, respectively, running as the user nobody (-u), allocating 1024  for object storage (-m). You should adjust the amount of storage to suit your needs; many memcached installs run with 4 GB. Once you are comfortable with your startup options, add the appropriate command to your startup scripts.

Create a /etc/init.d/memcached file and add above line to start memcached when the server boots

With memcached installed and running, it’s time to get PHP talking to the object cache. While multiple PHP API exists, the one in the PECL repository is recommended. If you are running a newer version of PHP, installation is as simple as:

# pecl install memcache

Or you can use following steps to install PECL memcache manually.

#cd /usr/local/src
#curl -O http://pecl.php.net/get/memcache
#tar zxvf memcache*
#cd memcache-*
#phpize
#./configure
#make && make install

Now we have to make sure PHP loads the newly built memcache.so library by adding the following line to php.ini:

extension=memcache.so

Now restart Apache:

Service httpd restart

Once it sucussfully install you can create phpinfo() on your webserver should now confirm that memcache is installed.

Regards
AlexP

How can you do that ?

After installing suhosin, remove all functions from disable_functions in php.ini and add in php.ini suhosin.executor.func.blacklist = “exec,passthru,shell_exec” and all the functions that you want to disable globally.

After that for each domain in the virtual host section you can add suhosin.executor.func.blacklist again but without the function that you need to enable. And so you will enable that function only for one domain.

Example:

<VirtualHost 127.0.0.1>
………..
………..
<IfModule mod_php4.c>
php_admin_value open_basedir “/usr/lib/php”
</IfModule>
<IfModule mod_php5.c>
php_admin_value open_basedir “/usr/lib/php”
php_admin_value suhosin.executor.func.blacklist = “passthru,shell_exec”
</IfModule>
…….
……
</VirtualHost>

In this example exec has been enabled for the VirtualHost. This way it will be better as you do not neet to modify all the virtual hosts only the ones that you need to enable one or more functions.

Regard’s

Alex P