As comments suggested probably Docker daemon is not running. AFAIK, docker is not supported for RHEL 6.4. Check Docker documentation:
Red Hat Enterprise Linux 6.5 Installation
You will need 64 bit RHEL 6.5 or later, with a RHEL 6 kernel version
2.6.32-431 or higher as this has specific kernel fixes to allow Docker to work.
Docker is available for RHEL6.5 on EPEL. Please note that this package
is part of Extra Packages for Enterprise Linux (EPEL), a community
effort to create and maintain additional packages for the RHEL
distribution. Kernel support
RHEL will only support Docker via the extras channel or EPEL package
when running on kernels shipped by the distribution. There are things
like namespace changes which will cause issues if one decides to step
outside that box and run non-distro kernel packages.
Warning: Please keep your system up to date using yum update and rebooting your system. Keeping your system updated ensures critical security vulnerabilities and severe bugs (such as those found in kernel 2.6.32) are fixed.