After-the-fact remote nohup with tcsh

This post may help. The recommendation is:

1. background the process (with Ctrl-Z, then bg)
2. run disown -h %[jobid] (likely a bash-ism, so you'll have to translate for tcsh)

The bad news, of course, is that the bg would need to be done in the same shell the process is running in... but ... it might already be backgrounded.

The really bad news is that the disown call might need to be done in the same shell. In which case, yes, you're screwed. But I'm not sure, maybe root can force-disconnect it.

Hmm. Possible good news -- tcsh does the disown automatically:

If tcsh exits abnormally, it disowns jobs running in the background automatically when it exits.

So, if your long-term process is already backgrounded, killing its tcsh parent should allow it to continue. The process is now disconnected from the starting terminal. (If not, see "bad news" above.)

Unfortunately, it's not screen, so there's no real reconnecting. You can fake it with gdb maybe (again, from the first link):

[...] with some dirty hacks, it is not impossible to reopen a process' stdout/stderr/stdin.

So you could still create a blank screen window (for instance that runs sleep).

And then use gdb for instance to attach to the process, do some call close(0)
call close(1)
call close(2)
call open("/dev/pts/xx", ...)
call dup(0)
call dup(0)
detach

The process' output would go to screen. It wouldn't be attached to that screen terminal, so for instance[sic] would kill the "sleep" command, not the process, but that could be enough for the OP.

I wonder if there shouldn't be "call dup(1)" and "call dup(2)" in that process as well...

These questions refer to a program called Cryopid which may help you. I don't have any experience with it, however.

Moving a process between hosts

Moving xterms between X sessions

Nohup and screen a process