That depends on how Linux is used in the business.
In most businesses there is not a primary Linux administrator. There may be a systems administrator who takes care of the servers, network, and telecom needs and maybe some or all of these needs utilize linux in some way. If this is the case then you would mainly install the OS, configure the system, create accounts, troubleshoot technical issues, etc.
In some businesses a profit center is tied in some way to linux, IE: a hosting company, or some other business that utilizes linux to provide a service to their customers. In this case your daily routine would encompass some or all of the previously mentioned duties along with some of the following: designing solutions, optimizing systems, customizing systems, etc
A good start to getting into linux sys admin work is to get a LPI certification.