# Multiple processes logging to single file

**URL:** <https://www.ruby-forum.com/t/multiple-processes-logging-to-single-file/138323>\
**Category:** Ruby\
**Created:** [May 22, 2008, 1:26am UTC](https://www.ruby-forum.com/t/multiple-processes-logging-to-single-file/138323 "2008-05-22T01:26:02Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![pachl](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/5f9b8f/32.png) [@pachl](https://www.ruby-forum.com/u/pachl)\
**Post date:** [May 22, 2008, 1:26am UTC](https://www.ruby-forum.com/t/multiple-processes-logging-to-single-file/138323/1 "2008-05-22T01:26:02Z")

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When using the native ruby logger, is it save to have multiple  
processes writing to the same log file?

For instance, I have the following ruby source example:

# test.rb

require ‘logger’

log = Logger.new(’/tmp/RLOG’)

20.times do  
log.error “PID: #{$$}”  
sleep 1  
end

log.close

# end test.rb

Then I execute like so:

$ ruby test.rb & ruby test.rb & ruby test.rb

After inspection of the log file, each process logged 20 times, all  
messages interleaved of course. It looks like it works, but am I  
delusional? I’m on an OpenBSD box. Does the OS handle caching/writing  
from multiple sources?

-pachl

---

<div class="post-metadata">

**Author:** ![pachl](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/p/5f9b8f/32.png) [@pachl](https://www.ruby-forum.com/u/pachl)\
**Post date:** [May 22, 2008, 1:48am UTC](https://www.ruby-forum.com/t/multiple-processes-logging-to-single-file/138323/2 "2008-05-22T01:48:52Z")

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pachl wrote:

| After inspection of the log file, each process logged 20 times, all  
| messages interleaved of course. It looks like it works, but am I  
| delusional? I’m on an OpenBSD box. Does the OS handle caching/writing  
| from multiple sources?

Yes, the OS should manage that (it is file-system level, rather than  
userspace level). However, you can tweak your code to have  
‘transactional’ logs (i.e. that every application logs a meaningful  
chunk of information in one go).

Anyway, the file system and drivers take care of the actual writing.

Though, having everything log into one logfile _may_ result in fractured  
files, or odd race conditions and/or deadlocks. It might be saner to log  
each process to its own file.

* * *

Phillip G.  
Twitter: [twitter.com/cynicalryan](http://twitter.com/cynicalryan)  
Blog: [http://justarubyist.blogspot.com](http://justarubyist.blogspot.com)

Don’t over-comment.  
~ - The Elements of Programming Style (Kernighan & Plaugher)  
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