brew update が出来なくなった時の対処

$ brew update
error: could not lock config file .git/config: Permission denied
fatal: Will not delete all non-push URLs
Error: Failure while executing: git remote set-url --delete origin .*mxcl/homebrew.*

Permission の問題っぽいのでそれっぽい所に移動する

$ cd $(brew --prefix)
$ ls -l
total 80
-rw-r--r--@   1 geshi  admin   3158 10 24  2014 CODEOFCONDUCT.md
-rw-r--r--@   1 geshi  admin    916 10 24  2014 CONTRIBUTING.md
drwxr-xr-x@  30 501    admin   1020  2 23  2015 Cellar
...

やっぱりなんか変

$ sudo chown -R geshi ./
$ brew update
error: The following untracked working tree files would be overwritten by merge:
    Library/Formula/agedu.rb
    Library/Formula/appledoc.rb
    Library/Formula/mydumper.rb
    Library/Formula/nailgun.rb
Please move or remove them before you can merge.

まだ出る。。。

$ git fetch origin
$ vim .git/config
$ git remote add origin https://github.com/Homebrew/homebrew.git
fatal: remote origin already exists.
$  git reset --hard origin/master
HEAD is now at cbbc9e5 gtk+3: update 3.18.7 bottle.
$ brew update
To restore the stashed changes to /usr/local run:
  `cd /usr/local && git stash pop`
Updated 1 tap (homebrew/dupes).
==> New Formulae
homebrew/dupes/bc       homebrew/dupes/bzip2    homebrew/dupes/krb5     homebrew/dupes/srm      homebrew/dupes/xar
...

出来た！