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The command that effectively denies all users from a specific host in the host.equiv file is represented by the syntax "-host". This notation indicates that access is denied to the host specified. In the context of the host.equiv file, which is used to manage trusted hosts in a network environment, entries typically dictate which hosts are granted or denied access rights.

When using the "-" sign before a hostname or a domain, it explicitly defines a denial of access, making it clear that users from that specified host will not be granted implicit access. This is important for safeguarding system integrity and ensuring that only authorized hosts can interact with the system.

In contrast, options with "+" usually indicate permission or allowance, while the "@" notation implies group permissions, making them unsuitable for denying access to specific hosts. Hence, they do not align with the objective of denying all users from a particular host as effectively as the "-host" command does.