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dtach is exactly what you're looking for.
There are other similar tools. I personally found zmx to be the best, but it's more feature rich than dtach, and might be more than you want. Dtach is pretty minimal. But my only issue with it is it struggles with reloading a terminal session for a TUI that needs non trivial redrawing.
Yeah! It got mentioned earlier, and I've started playing with it -- it's not perfect like you say, but it is good enough for what I need
I think the tool "dtach" might fit the bill.
It's supposed to be a lightweight replacement for tmux/screen that only does the detach/reattach parts, and none of the terminal emulation stuff or windowing or any of that.
Like many have already said, your probably just looking for a terminal multiplexer. Things like screen or zellij, which to my knowledge also don't require any kind of "server". You start a process and the tool provides means to reattach to the still running sessions.
Any session gets a name, which is what you can use to reattach to a specific one, or you can just "attach" if there isb only one available.
I googled it for you and found this: https://serverfault.com/questions/24425/can-i-nohup-screen-an-already-started-process
It doesn't create a file, but you don't need one. Read all the answers for options on reattaching. I haven't used it, so I can't vouch for any of them. (Personally I just use byobu and have it start with each shell, so I'm always running tmux.)
I don't think there's any system that can reliably freeze a single process to disk. Usually that's implemented by the program itself.
Cryopid seems promising from that, thanks!
This is a very confusing question. What is the concern about this file, and what do you mean about "reattach"? Is it a long running process? Why would locking thw file, or working in memory of tmp not work? Why is screen not an option?
Imagine you want to launch 1000 long standing processes as oneshots.
Nohup to a file would be a better usage than a screen multiplixier
Why:
"But you can extract a snapshot of your 1000 tmux windows to file and grep that for status!"
Yes, great, but it's not a neat solution, and tmux/screen snapshots might not capture everything due to window rendering artefacts.
But what's in this file?
If you're just shuffling data around, use a database.
Log data, current status of a run, timestamp of an error, you name it.
These are oneshots. Of course you could use a proper workflow system with data provenance and lineage tracking baked in, but during the dev cycle of something new you usually want to play around and gather metrics first without worrying first about the architecture.
Please don't X/Y me.
You're right. A data ase would be absolutely stupid. Use a log shipping library instead.
Also, don't A/B me.
Don't both require me to know the nature of the data beforehand?
Please don't B/M on me
Oh a systemd-logger, I dont have access to the logs, only the admin does. Plus I can't reattach to the process that way
You can use it to log to a defined file in userspace. You don't need to "reattach" to the process because all of the output goes through this util. Use signal handling to control the process.
You're probably right that that's likely enough for non-interactive tools
oh wow, an actual answer without the classic "this is an X / Y problem" snark!
Re-redirect looks like what I want, thank you kind stranger!
Not sure what you want. You're trying to monitor that process so you can tell when it finishes? You want to know when the file is closed? You can do that with inotify(2).
I essentially want tmux, without the hassle of needing a tmux server running in the background.
I want the convenience of nohup, with the ability to attach to the nohup file of a running process and recover the running session.
hassle of needing a tmux server running
What do you mean? What hassle??
I use "screen" which i guess is similar to tmux, if that's of any help.
The tool is "screen" but it isn't going to a file per se, just a session name. Edit: I guess tmux does the same. What do you see as the difference? Are you trying to also suspend execution so you can reboot?
the use-case is to simply re-attach to a long-running process, I'm not too concerned about a session persisting across reboots, though that would clearly be amazing
Screen should work with no problem. You just start the screen session, detatch when you want, reattach later. No problem.