See output of a background process

Question

I'm testing on Debian a routing algorithm wrote in C. In algorithm source file i set a flag to 1 to enable the printing of routing decisions on stdout. Problem is: the process that runs this file is a background process. How can i see stdout?

score 4 · Answer 1 · edited Apr 02 '14 at 14:53

4

You can use the below line to check what your process is doing.

$ strace -p $!

$! gives the process ID of the last background process. Remember to run the above line in same console as the background process.

edited Apr 02 '14 at 14:53

3cheesewheel

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answered Oct 03 '13 at 14:03

neo

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What if the original console is disconnected and I have to login on from another console ? – Lewis Chan Dec 20 '18 at 01:59

score 3 · Answer 2 · edited May 23 '17 at 12:06

Assuming you have the process you want to listen to already up and running, and you don't want to stop and rerun it with a redirection as Laszlo suggests: you can use strace to listen to it - How should strace be used?

Basically it can track all system call activities, but that includes printing

Add -p <pid> to attach it to your desired process. Add -e write to filter most of the stuff and get only the output writes

For e.g.:

> grep somestring . -R >& /dev/null &
  [2] 8093
> strace -p 8093 -e write
...here goes the output...

score 1 · Answer 3 · answered Oct 03 '13 at 11:47

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You redirect the output of your program into a file, and then you can watch the output in that file.

answered Oct 03 '13 at 11:47

Laszlo Valko

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See output of a background process

3 Answers3