What's the difference between nohup and &?

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http://unix.stackexchange.com – It is commonly said that "&" puts the process into background execution, but that process would be killed when terminal is closed. But from what I see, everything I sent into background was continuing to be active long after I close the terminal. For example: $ tail -f /var/log/messages/ & That process would continue to run, even if there are no other process under the user that launched it, and all terminals are long gone. Why is that? (HowTos)