Final answer:
The intended operator cannot perform the action of rebooting because in Configuration file 2, the SSH command is configured with 'no-pty', which prevents the allocation of a pseudo-terminal required for interactive sessions.
Step-by-step explanation:
The question presents a scenario where an operator is supposed to have limited permissions, specifically to reboot remote hosts but not perform other actions. We are given snippets of different configurations that are potentially causing an operator to be unable to perform the intended action of rebooting.
The correct answer is D. The SSH command is not allowing a pty session. This can be inferred from Configuration file 2, where it specifies no-pty, which stands for "No pseudo-terminal". When no pseudo-terminal is allocated, the operator cannot have an interactive session, which would be required to run the reboot command interactively.
The sudoers configuration in Configuration file 1 (/sbin/reboot) seems to be correct, hence, option A is unlikely. Configuration file 3 lists a shell for the operator, which does not directly prevent them from rebooting; therefore, option C is incorrect as well. Option B suggests that SSH command shell restrictions are misconfigured, but the issue is specifically with the pty allocation rather than general SSH command shell restrictions.