They ask about proficiency in several technologies used by the department. E.g., Linux, CentOS/RHEL, Kickstart, VMware, cfengine, etc. You are not assumed to know everything, but if it is on your resume, you should be familiar with it. They will pick a few specific questions about a certain technology to verify you really know it. They might ask about your past experience at previous jobs and your future goals to see if this job is a good fit for you. They do not want to hire someone who will not be satisfied with the position and leave soon after being hired.