On Call vs. On-Duty
What is the difference between on-call and on-duty for a system administrator?
During on-call sysadmin is reacting to alerts and paged calls when things are not working. During the day busy with regular projects, but prioritises on-call responsibilities.
During on-duty sysadmin handles full operational state of the system. Reacting to alerts and calls, responding to developer requests, resolving issues that occur. Improving monitoring and infrastructure on the go. During the day focused on duty, not working on any projects.
On-call - reacting when called, on-duty - being the one in charge of the whole system operation.