What to do if your Rails application cannot connect to Mysql?

When I use my Mac to continue developing my Rails application using Mysql as the database system. It first initialized and developed in Ubuntu.

After bundling tasks, I move to rake db:create to initialize my databases for development and test environment. But the problem comes out:

Mysql2::Error: Can't connect to local MySQL server through socket '/var/run/mysqld/mysqld.sock'

Ok, cd to the


Oh, there’s no mysqld.sock there. Ok, so there must be the error as above error message.

So, I was wondering where mysqld.sock is in my computer? I was installed Mysql through brew and able to connect to Mysql by Mysql Workbench with no problem. So let’s see some variables. Enter to the terminal:

mysqladmin -p variables | grep socket

Provide the password, and then you will see something like:


| performance_schema_max_socket_classes                    | 10

| performance_schema_max_socket_instances                  | -1

| socket                                                   | /tmp/mysql.sock|

Wow, there comes in the socket line the mysql.sock file location

We have to connect through it.

After some research, I know that Rails settings the socket in the filedatabase.yml.

So, it’s EZ now, just replace the new found path.

It’s ok now. I can continue my work.


Fixing rbenv not update ruby system (rbenv version different from ruby -v)

Recently, I faced with the problem of not syncing ruby version with my Mac.

My project requires ruby version >= 2.2.2 but default version is 2.0.0.

I haved installed ruby 2.3.1  on my rbenv (ruby version manager) and set it global, but when i bundle install, there comes some error liked:

activesupport-5.0.0 requires ruby version >= 2.2.2, which is incompatible with the current
version, ruby 2.0.0p648

Even rbenv version shows:

2.3.1 (set by /Users/duchoang/.ruby-version)

I checked back with ruby -v, it shows 2.0.0. Oh shit what happened?

I searched and they said that I have to install ruby-build, ok but after that I reallized that it’s not the cause:

brew install rbenv ruby-build

rbenv rehash

I reallized that I’ve switched to zsh, so instead of ~/.bash_profile I need to rerun the following command to ~/.zshrc:

$ echo 'if which rbenv > /dev/null; then eval "$(rbenv init -)"; fi' >> ~/.zshrc
$ source ~/.zshrc