How to connect to a disconnected process ?

[Ping Zhou]

I have been annoyed by this for quite a while - being disconnected due to modem
or other reasons, and I have to relogin and redo a lot of things. So I have
been wondering - is there any way and/or software that will let you to
reconnect to the disconnected process when, or after, you relogin ?  Or
just for the purpose of education, what does it take to realize this on
Unix machines (VMS does this when you relogin) ?

Any help will be appreciated. (If this has been discussed before, email please)

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Ping zhou at linac.fnal.gov