This is old problem for mostly drupal newbies but I see its not explained properly what should be best practice.

So to do this properly you should

I had many vagrant machines and haven't really paid much attention to setting unique hostname, machine name and IP address, which resulted in mixed environments. Meaning I loaded one URL and I got files and database from the other vagrant machine. To debug what was really happening I went into devel/php and found out where is my mind I mean Index file :) to do that I echoed it like this.

UPDATE: This is changed now and author wants that we install drupal launcher and then drupal console per project as stated here so composer global require is no longer supported

https://docs.drupalconsole.com/en/getting/project.html

You may get this message trying to update drush globally via composer,
"To initialize a project, please create a composer.json file as described in the...."

so lets make it sure both are globally installed and required.

Download phar file with

curl -sS https://getcomposer.org/installer | php

then move it to /usr/local

To see where CLI settings are type

php --ini

It is possible that you will get this:

Find a commit hash where merge occured to master and then

git revert -m 1 <commit-hash> 
git commit -m "Reverting the last commit which messed the repo."
git push -u origin master

Lets say you need to put something to LIVE site fast. And you go and check what is currently in line to get pulled once you fire git pull (https://itportal.foreo.com/documentation/card/1011)   and see there are other branches/commits coming and you are dont know is it LIVE material. There is a side route for this cases.

Lets say you go to production site GIT and fire "git pull" command, something goes wrong, there are conflicts and you start to panic. Proper solution for this is to write

git reset --hard

This will clean the mess and put GIT to state before this.

Before final git pull to LIVE site, it is a good idea to check what is going to be pulled. So to do that

In case ajax calls are making a trouble and developer needs more information about what is happening regarding: