Allow WordPress write access to Docker mounted folder

[admin]

I have a Docker setup that works well with Ubuntu, Nginx, PHP-FPM and MySQL.

WordPress can write to the uploads folder and I can edit templates online, but when I try to upgrade WordPress or plugins, it fails with:

<blockquote>
Unpacking the update…

Could not create directory.: wordpress

Installation Failed
</blockquote>

I have

chmod 777

the entire WordPress folder, so I'm not sure if this is Docker or WordPress related. I have also checked various logs, but the only relevant line I found is this:

<blockquote>
192.168.59.3 - - [01/Oct/2014:14:16:58 +0000] "POST /wp-admin/update-core.php?action=do-core-upgrade HTTP/1.1" 200 5576
"/wp-admin/update-core.php" "Mozilla/5.0
(Macintosh; Intel Mac OS X 10_10_0) AppleWebKit/537.36 (KHTML, like
Gecko) Chrome/37.0.2062.124 Safari/537.36"
</blockquote>

Here's how I created the Docker environment:

<pre class="lang-sh prettyprint-override">

brew install docker boot2docker
boot2docker init
# Allow VM access to our space
curl http://static.dockerfiles.io/boot2docker-v1.2.0-virtualbox-guest-additions-v4.3.14.iso > ~/.boot2docker/boot2docker.iso
VBoxManage sharedfolder add boot2docker-vm -name home -hostpath /Users
boot2docker up

Here's how I start the container:

<pre class="lang-sh prettyprint-override">

docker run -p 80:80 --name wp -d -v ~/wordpress:/mnt/www:rw wp

Here's the Nginx configuration:

server {

    listen   80; ## listen for ipv4; this line is default and implied
    listen   [::]:80 default ipv6only=on; ## listen for ipv6

    root /mnt/www;
    index index.php index.html index.htm;

    # Make site accessible from http://localhost/
    server_name localhost;

    location / {
        # First attempt to serve request as file, then
        # as directory, then fall back to index.html
        try_files $uri $uri/ /index.php?q=$uri&$args;
    }

    #error_page 404 /404.html;

    # redirect server error pages to the static page /50x.html
    #
    error_page 500 502 503 504 /50x.html;
    location = /50x.html {
        root /usr/share/nginx/www;
    }

    # pass the PHP scripts to FastCGI server
    #
    location ~ \.php$ {
    try_files $uri =404;
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        # NOTE: You should have "cgi.fix_pathinfo = 0;" in php.ini

        fastcgi_pass unix:/var/run/php5-fpm.sock;
        fastcgi_index index.php;
        include fastcgi_params;
    }

}