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I am trying to install OpenCV with Homebrew.

After typing

sudo brew install opencv 

I get this error message

Cowardly refusing to sudo brew install

How can I solve this?

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You do not need sudo for Homebrew

As OpenCV now exists in homebrew/science, run the following:

brew tap homebrew/science
brew install opencv

Homebrew never needs elevated privileges for anything – except for when there are some conflicts with other installed libraries:

Homebrew is designed to work without using sudo. You can decide to use it but we strongly recommend not to do so. If you have used sudo and run into a bug then it is likely to be the cause.

If you can't install it without sudo, make sure you own /usr/local and have the correct permissions – also by running this script. Running brew doctor will also generally give you some good hints.

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If I do that I get: Cannot write to /usr/local/Cellar – luckyo Feb 17 '12 at 13:21
2  
Did you ever mess around with chmod, possibly in combination with sudo there? Try sudo chown -R $USER /usr/local. Does it work after that? If not, please post a complete ls -la listing of /usr/local and what brew doctor says. – slhck Feb 17 '12 at 13:23
1  
Warning: It appears you have MacPorts or Fink installed. Software installed with other package managers causes known problems for Homebrew. If a formula fails to build, uninstall MacPorts/Fink and try again. Error: Unsatisfied external dependency: numpy Homebrew does not provide Python dependencies, easy_install does: easy_install numpy – luckyo Feb 17 '12 at 13:26
1  
Ahah, see, we're getting there. For the future, please include things like these in your question, we can't magically guess anything. I don't understand your latest question … please edit your original post and include the ls -la of /usr/local. Also, maybe think about uninstalling MacPorts or Fink, whatever you have. – slhck Feb 17 '12 at 13:28
1  
That's probably not enough info. The group should probably be staff. But … this is the third time I've asked: Please post the complete output of ls -la /usr/local in your original question. – I'm glad to help, but you need to help a bit as well! – slhck Feb 17 '12 at 13:42

The install script of opencv wants to link the libraries into /usr/local/lib, but that directory needs higher privileges. Even if brew refuses to install as root, you can just use

sudo brew link opencv

after you ran sudo install as a user. This worked for me.

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as another answer says, you should note that: "Homebrew is designed to work without using sudo. You can decide to use it but we strongly recommend not to do so. If you have used sudo and run into a bug then it is likely to be the cause." – meduz Feb 3 '14 at 8:41

I have run into this same issue. A quick fix is to manually create the /usr/local/Cellar folder, then try again without sudo.

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