Level099: 2: Bash jobs: bg while suppressing output?

Level1Techs INBOX.deb
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So, I thought I’d edit a file while docker was going up on a bootstrapped ssh connection (so forgot to use a multiplexer):

podman-compose up -d
Ctrl-z
bg
vim…
# screen filled with progress bar dump

Searching around, you can do that before executing by subshelling it: (ping 1.1 &)

How do you background a job, without listening to stdout (and stderr)?

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If you aren’t using Ctrl+Z, try & > /dev/null so something like ping level1techs.com > /dev/null &

If you’re using Ctrl + Z, it gets way more complicated. I think there might be a way to intercept the stdout with gdb (GDB: The GNU Project Debugger) and redirect that to /dev/null but it’s probably not worth the effort.

EDIT: bash - Redirect stdout/stderr of a background job from console to a log file? - Super User

gdb -p <PID> and then:

p dup2(open("/path/to/file",577, 420), 1)
p dup2(1, 2)
detach
quit

Now I’m going to do the classic Linux “You’re doing it wrong and here’s how to avoid the problem, but not solve it”: If it’s a big job I am always running it in nohup anyways. So nohup ping level1techs.com & will get it and run it silently in the background, redirecting stdout to nohup.out. And if you close the terminal, it’ll stay alive.

It’s too bad nohup bg %n or bg %n > /dev/null doesn’t work.

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Attaching a debugger to a process as a general rule slows the process down. Haven’t tested or thought about this, if the gdp -p actually slows stuff down.

I’m pretty much always running a multiplexer (byobu¹) anyway. Somewhat retiring the need for jobs (besides suspending).

¹ I’ve found it to be more explorable and user-friendly than tmux, it has everything I’ve ever needed, and more. See the cheat sheet.

Level099: 3 should probably be about multiplexers…?

If I know I don’t want output before, I’ll redirect to somewhere, or again, use a multiplexer.

The thing is, there are moments, where I thought I’m going to be in for a moment, and not bother running/enabling a multiplexer.
The idea of ‘well now I’m waiting for computers for no reason, while I could do something else on the same device’ only comes up after ~5-10s of running the command.

So – it’s just not a use case thought of, and not reasonably possible.

4

Try :
nohup command
ctrl-z
bg

Used like this, nohup will ignore input and put output into a file called nohup.out

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-1

You can nohup, redirect to /dev/null, etc.
Problem being, you have to redirect output before executing. You can’t, afaik, change it in the middle of execution.

7

If you want to ignore the stdin and stderr then Just start a new terminal, its handy to have a key-binding for this. If there is some issue with a new terminal then install something like gnu-screen and use it to manage virtual terminals.

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If the OP’s problem is only the fact that the text displayed is the console output instead of the file content in vi, then a ctrl-g will clear it and display the file content…

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