Capistrano mkdir permission denied

By default Capistrano 3 deploys to /var/www which is not writable by deploy user. You need to change the ownership of /var/www to deploy user using the following command.

sudo chown deploy:deploy /var/www/

After this, you should be able to deploy your app without permission error.

Credit to Bob Roberts.

I think this should be an answer as its easy to miss your comment. I know I missed it few times.

sudo chown -R deploy:deploy /var/www/

or whatever your username is

sudo chown -R username:username /var/www/