Unicorn – "’raise_if_conflicts’ can’t activate rack" error

If you’ve been trying to start a Unicorn app and seeing something like the following error:

“‘raise_if_conflicts’: can’t activate rack-1.4.1, already activated rack-1.5”


It’s down the versions of rack gem which you installed. In your applications gemfile you should specify the version of rack you want to use, e.g.

gem “rack”, “1.4.1”

Run “bundle update rack” and see if that fixes the issue.

If not, run “gem uninstall rack”, you may see that you have two versions of rack installed, uninstall the wrong one and try again.


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