By default vSphere does not provide client for Linux or OS X. You need to use Windows system to manage your VMware ESX server. However, it does provides vSphere Web Access which allows you to organize and share virtual machines using web browser. If you try to access vSphere Web Access you may get an error which read as follows:

503 Service Unavailable

You can fix this problem as follows.

Login to your vmware server as root user.

Type the following command to turn on the service:
# chkconfig vmware-webAccess on
# service vmware-webAccess start

Now login as root to your server:

Alternatively, you can use MS-Windows vSphere client to start and stop vSphere web access services without using shell prompt.