Installing ssh2 support in PHP
Most distribution has the SSH2 library packaged for PHP, but this is not the case for example if you are running CentOS 6 with php55w installed.
In this case you need to manually install some prerequisites and compile it.
yum -y install libssh2-devel yum -y install php55w-pear yum -y install php55w-devel pecl install ssh2-0.13
And then add extension=ssh2.so to php.ini and restart httpd