nohup output redirection to a different file

Question

I use nohup quite often for important long running processes under linux/bash, so much so that nohup time my command with arguments && mv nohup.out my.log is almost an idiom for me.

The problem is that nohup puts both stdout and stderr into nohup.out, and I cannot control the name of the file. This means that if I accidentally start two nohups in the same directory, their output will be interleaved in nohup.out.

The questions are:

How do I deal with this problem? Always running nohups in separate directories and writing a shell function which will first check for ./nohup.out are two sucky options I see.
How come I cannot tell nohup where to redirect the output? GNU tools tend to have so many options, why not nohup?

score 9 · Accepted Answer · answered Feb 14 '13 at 15:44

9

You can redirect both stdout and stderr to one file. With Bash 4 (or others such as Zsh), as easy as:

nohup <some-command> &> output.log

I can't tell you why there's no separate option for nohup to set the output, but if your shell can take care of that, you don't really need an option.

answered Feb 14 '13 at 15:44

slhck

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Will it prevent `nohup` from performing its own redirection? – u1686_grawity Feb 14 '13 at 15:45
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GNU `nohup` says that it'll redirect stdout to a file if you specify `nohup command > file`. BSD `nohup` doesn't mention this at all, but it worked for me. – slhck Feb 14 '13 at 15:50
*GNU nohup says that it'll redirect stdout to a file if you specify `nohup command > file`* Isn't redirection in case of `nohup command > file` being handled by shell and not `nohup`? If so then how can `nohup` take any action based on weather redirection is present or not? – Piotr Dobrogost Jan 21 '15 at 08:29
The file `nohup.out` will be created in the case of error output, too; but if you redirect both stdout and stderr, there cannot be any output, so the file will not be created. But the `&>` syntax is not POSIX-compliant; you're better off with the answer by Irshad Khan elsewhere on this page. – tripleee Apr 20 '18 at 07:14

Irshad Khan · Answer 2 · 2018-04-20T07:10:28.130

6

To Append output in user defined file you can use >> in nohup command.

nohup php your_command >> filename.out 2>&1 &

This command will append all output in your file without removing old data.

edited Apr 20 '18 at 07:10

answered Aug 18 '17 at 15:10

Irshad Khan

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And if you want to overwrite the output file using POSIX `sh` syntax, that's simply `nohup your_command >filename.out 2>&1 &` – tripleee Apr 20 '18 at 07:15

score 3 · Answer 3 · answered Feb 14 '13 at 15:48

There are more ways than just nohup to start a process so that it would ignore SIGHUP; for example: (written as shell functions)

nohup() {
    setsid "$@"
}

nohup() {
    ("$@" &)
}

nohup() {
    "$@" & disown
}

(setsid, or even (setsid "$@" &), might be the best choice.)

All of them allow you to specify your own redirections with >, 2>, and &>/>&.

nohup output redirection to a different file

3 Answers3