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Old 04-14-2011, 06:02 AM   #1
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nohup outputs

Dear all,

I have been looking around in the forums and did some googling, but I could not find a solution to my problem.

I have to launch a code on a remote machine which has two types of output:
1) A lot of continuous messages in the stout (the display)
2) Every once in a while (let's say every hour) the code also writes a "solution" into files.

What I would like to do is to launch the code and keep it running even if I disconnect from the remote machine.

Well, the first solution I tried was a simple
$ nohup ./code &
which does the job but creates a file (nohup.out) which is way too large (talking about several tens or hundreds of Gb).

So I was not happy with this and I went for a
$ nohup ./code > /dev/null &
and I was very happy until I realised that the program is not writing the
"solutions" anymore. I guess is sending it to null.

By chance, I found that removing the nohup.out file while the program is running makes the deal: the code keeps running, the stout is redirected nowhere (I guess it cannot find the file so it forwards it to null), AND
I have my solutions file.

I was wondering if there is another, proper, correct way to do this, since I feel I am cheating a little.

A nice thing to do would be to actually write the nohup.out file, but limitating it in size: i.e. overwriting it when the file becomes too large.

I hope there is a solution! In any case, thanks for listening!
Old 04-14-2011, 09:10 AM   #2
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What is the "solutions" file?

Is it stdout or stderr? Does the program creeate a file? If so, where?
Old 04-14-2011, 11:10 AM   #3
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You have several options

I'm not exactly sure what you want, but here's what I typically do to run background jobs:
  $ ./code &
  $ disown
Using nohup should do more or less the same thing, except that nohup redirects stdout (output to the screen) to nohup.out. nohup will also redirect stdin from /dev/null, but that's what you want for background jobs anyway.

I have no idea without knowing the source of 'code' why it does write a file when you redirect stdout but doesn't if you don't. Is it a shell script or a compiled program? Either way, redirecting stdout to /dev/null shouldn't get rid of a file written during normal execution.
Old 04-17-2011, 03:57 PM   #4
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Hello all,

thank you for your replies.

The program I use is a g95-compiled program. The output files are created by the files itself, and (I guess) it is stout.

I will try the disown command and let you know if it solves the problem.



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