Cowardly refusing to `sudo brew update` or failure

First find out what is the current ownership of the installed package of brew (you will need this info in the last step)

ls -al `which brew`

Change the user and group of brew to root and wheel respectively:

sudo chown root:wheel `which brew`

Now execute your brew command as root, for eg. sudo brew link mcrypt. Lastly, revert back the ownership of brew to what you had found out in step 1 above

sudo chown : `chown brew`

brew update failure while executing git checkout

$ cd `brew --prefix`$ git remote add origin https://github.com/Homebrew/homebrew.git$ git fetch origin$ git reset --hard origin/master$ brew updateAlready up-to-date.