“Revisr is a Git and WordPress database plugin that allows you to keep track of your web projects in version control. Revisr eliminates redundant interfaces in your workflow and allows you to focus on the task at hand.” – Revisr

That sounds well and good. However, configuration required a few steps and below we document them.
It is needed to install git, create certificates, upload them to github, and also set appropriate permissions.

Steps

1. Temporarily allow login by the www-data account.
   Open /etc/passwd with nano or vi, and replace :usr/sbin/nologin with :/bin/bash
   See: http://programster.blogspot.gr/2014/05/ubuntu-1404-allow-login-as-www-data-user.html

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2. Install git.

   sudo apt-get install git

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3. Create a certificate for www-data user and set permissions.
   a) Go to www directory and change owners:

   ~/# cd /var/www
   /var/www# chown www-data .
   

   b) Generate a certificate:

   sudo -u www-data ssh-keygen -t rsa
   

   You shouldn’t enter a passphrase and you should see the correct key.

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4. Open the generated certificate and copy the text inside:

   root@server:/var/www/# cd .ssh
   root@server:/var/www/.ssh# cat id_rsa.pub
   ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAABAQDOL…etc

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   Go to Github site and upload the certificate.
   A) See step 4 of https://help.github.com/articles/generating-ssh-keys/
   B) Add your specific key to the github website at: https://github.com/settings/ssh

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6. Test the connection to github:

   sudo -u www-data bash
   ssh -T [email protected]

   You should see:

   Hi username! You've successfully authenticated, but GitHub does not # provide shell access.
   Type "Exit" to exit www-data terminal and type "sudo bash" to start root terminal.
   

   Type:

   exit
   sudo bash

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   Go to the wordpress directory and set the correct permissions. Reference: http://stackoverflow.com/questions/18352682/correct-file-permissions-for-wordpress

   chown www-data:www-data -R *          # Let apache be owner
   find . -type d -exec chmod 755 {} \;  # Change directory permissions rwxr-xr-x
   find . -type f -exec chmod 644 {} \;  # Change file permissions rw-r--r-

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8. Create a github repository and then connect revisr with this:
   Use the notation for SSH remote URL ( do not use https address).
   Example: in Remote URL enter: [email protected]:developerAccount/project.git

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9. Create a github repository inside the wordpress folder (see here for more info):
   A) Go to your folder and execute

   git init

   B) You should now be able to add and commit files using either the command line or the revisr command panel

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10. Check to see that permissions are correct for your wordpress git repository. You can run ls -lqa to check the owner and check within the .git folder as well. The following commands should be sufficient to set correct ownership to www-data:

    chown www-data:www-data -R .[^.]*
    chown www-data:www-data .
    

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The following steps should do it. Post your comments or questions below or send me an e-mail.