Jenkins console output not in realtime

Question

Pretty new to Jenkins and I have simple yet annoying problem. When I run job (Build) on Jenkins I am triggering ruby command to execute my test script.

Problem is Je

Answer 1

The Operating-System is buffering output-data by nature, to save CPU, and so does Jenkins.

Looks like you are using a shell-command to run your Ruby script -
I suggest running your Ruby script directly via the dedicated plugin:

Jenkins Ruby Plugin

(may need to install it)

Answer 2

Easiest solution here is to turn on syncing buffer to output. Something that @Craig wrote about in his answer but one line solution that will cover whole script, and not require you to flush buffer many times.

Just write

STDOUT.sync = true

Logic behind is simple, to avoid using IO operations many times output is buffered. To disable this use

STDOUT.sync = false

This is Ruby solution ofc.

Answer 3

For some commands, including tee a the best choice for unbuffering is a program called unbuffer from expect package.

Usage example:

instead of

somecommand | tee /some/path

do

somecommand | unbuffer -p tee /some/path

Sources and more info:

• https://stackoverflow.com/a/11337310/2693875
• https://unix.stackexchange.com/a/25375/53245

Answer 4

Make sure your script is flushing its stdout and stderr. In my case I had a buffering issue similar to what you describe but I was using python. The following python code fixed it for me:

import sys
sys.stdout.flush()

I'm not a Ruby coder, but Google reveals the following:

$stdout.flush

Answer 5

It seems to me that python -u works as well.

E.g. In batch command

python -u foo.py

Answer 6

The other answers are correct in saying that you need to ensure standard output is not buffered.

The other thing to be aware of is that Jenkins itself does line by line buffering. If you have a slow-running process that emits single characters (for example, an nunit test suite summary that prints a . for a successful test and an E for an error) you will not see anything until the end of line.

[True for my Jenkins 1.572 running on a Windows box.]