Wordpress: All posts show 404 Error, Mod_Rewrite is on? .htaccess being read?

I got caught up this week with an annoying problem between a new web host, Linode.com, and an old WordPress transfer.

After setting up all the instruction that Linode provided for a new web server (which were very good, by the way), downloading a new copy of WordPress files, and moving the MySQL database and images, I kept getting 404 Error Not Found.

The front page worked fine. The WordPress administration worked fine. And, when I would go set the Permalinks to being query for the Primary Key of the post, I would see the post.

This pointed to a problem with Apache and its rewrite function.

Apache recognizes special files that are used to configure the site (or an individual directory) called .htaccess files. Sometimes the problem with these files is that access permissions are not correct. Sometimes the system needs to have an extra line inserted at the top:

  Options FollowSymLinks

or

Options +SumLinksIfOwnerMatch

WordPress requires the ability to write to the .htaccess file when the Permalink structure is changed. So, per multiple versions of instructions, I changed it to chmod 777 -- this grants full read-write privileges to anyone.

I wiped the file clean, and then hit the Permalink button. Wordpress wrote what it needed to just fine, but it was the same thing that had already been there. Not the problem. So, I set the chmod back without the writing privileges.

Someone suggested insert a line to cause a 500 Internal Server error -- to add the words "This is garbage" to the middle of the code. If the file was being recognized at all, there would be an error. If the file was not being recognized, nothing would happen. Nothing happened
.
So, I went back to the Apache config files of Linode.
I was installing a Ubuntu LAMP configuration, and there is a couple of things involved.

There is a main configuration file:
  /etc/apache2/apache2.conf

There are also a couple of other files involved in configuration:
  /etc/apache2/sites-enabled/
  /etc/apache2/sites-available/MYSITENAME.conf
  /etc/apache2/sites-available/000-default.conf

I had a problem with 000-default.conf earlier. It was the, duh, the default configuration, and when I would go to the IP address, I would get the 000-default.conf directory (which was /var/www). I had already disabled this default setup, so that wasn't the problem.

Someone suggested that I needed to fix the rewrite directive in the MYSITENAME.conf file.
But there wasn't anything in there that referred to rewrite or AllowOverride.

So, I turned to the apache2.conf

There I found the AllowOverride directives, but none of them had anything to do with MYSITENAME.

The first entry looked like this:
<Directory />
  Options FollowSymLinks
  AllowOverride None
  Require all denied
</Directory>

I changed it to AllowOverride All, and it worked.
So, to restrict the level of access, I changed it back to None, and I added  this code to the bottom of the virtual host configurations:

<Directory /PATH/TO/MYSITENAME/>
  Options FollowSymLinks
  AllowOverride All
  Require all denied
</Directory>

"/PATH/TO/MYSITENAME/" obviously should be changed to whatever the path is to your public website directory. 

It works great now.