You don't have write permissions into the /var/lib/gems/1.9.1 directory

Question

I got this error, for all gem that I try to install:

ERROR: While executing gem ... (Gem::FilePermissionError) You don\'t have write permission

Answer 1

Either run with sudo or if that doesn't work, try sudo chmod +w <file> (from terminal separately)

Answer 2

According the question I see a few steps in order to allow writing to /var/lib/gems:

1. Create gems (if not any) group, and add yourself to the group:

   $ groupadd -f gems
   $ usermod -aG gems $(whoami)
   

2. When reenter to the session:

   $ sudo -u $(whoami) bash
   

3. Allow write for a gems group to /var/lib/gems/, and set the setgid bits:

   $ chown :gems /var/lib/gems/
   $ chmod g+sw /var/lib/gems/
   

4. Try installing gems into /var/lib/gems/.

NOTE: I strongly advice you to control rubies and gems via rbenv/rvm keeping them in a local home folder. Please refer to the answer to know how to properly setup your project.