gem install permission problem

Try setting GEM_HOME and GEM_PATH to ~/.gem,

For the current terminal session, just type:

export GEM_HOME=~/.gem
export GEM_PATH=~/.gem

If you want these to be set whenever you open a terminal, add the above commands to your ~/.bashrc file.

For a more comprehensive solution to setting up a custom ruby environment, see this tutorial from Site5KB, which describes using a .gemrc file.

For a systemwide Ruby install, become root. For example:

$ sudo gem install hpricot

However, the modern approach in many circumstances, including in development, is to use a tool that lets you easily install and use Ruby as a normal user. This lets you avoid having to become root. There are a few such tools, and the one I use is RVM.

# install rvm into your ~
$ \curl -sSL https://get.rvm.io | bash -s stable

# install latest version of ruby into your ~
$ rvm install ruby

# installs a gem into your ~
$ gem install $SOME_GEM_NAME

I was getting this error on my shared server through 1and1 hosting. my solution was adding the --user-install option, which just installs it for your logged in user (which is all you need in a shared server environment) example; installing sass

gem install sass --user-install

If you're using rbenv and this is happening, you need to add the following to your .bash_profile:

export RBENV_ROOT="$HOME/.rbenv"

if [ -d $RBENV_ROOT ]; then
  export PATH="$RBENV_ROOT/bin:$PATH"
  eval "$(rbenv init -)"
fi

re-install ruby resolve my problem.

brew install ruby