simplify and fix installation instructions

* install.md, install-manual.md, and easy-install.md had a lot of
  redundancy. Rework them so the common prefix and suffix are in
  install.md and it's clear when to navigate back and forth. This
  removes from very stale references to prep.sh and cameras.sql in
  install-manual.md (which never should have mentioned these scripts
  anyway).

* remove all the SAMPLE_MEDIA_DIR, SAMPLE_FILE_DIR, and
  SAMPLE_FILE_PATH stuff from the scripts. This was too complicated
  (one variable will suffice) and inconsistent in terminology (a
  couple "samples dir" occurrences slipped through review; they
  should have been "sample file dir"). It also wasn't really useful
  enough because the procedure for a mount point is manual anyway,
  and because some installs will have multiple sample file dirs
  anyway.

* in the mount point procedure, fix the paths to be consistent. Also
  describe the "nofail" and "Requires=" config I have on my machine.

* fix some incorrect info about how to use "moonfire-nvr config" and
  describe "flush_if_sec".

guide/install-manual.md

@@ -1,14 +1,9 @@
-# Installing Moonfire NVR
+# Building and installing Moonfire NVR manually
 
-This document describes how to install Moonfire NVR on a Linux system.
-
-## Downloading
-
-See the [github page](https://github.com/scottlamb/moonfire-nvr) (in case
-you're not reading this text there already). You can download the bleeding
-edge version from the command line via git:
-
-    $ git clone https://github.com/scottlamb/moonfire-nvr.git
+This guide will walk you through building and installing Moonfire NVR manually.
+You should have already downloaded the source code as mentioned in
+[install.md](install.md), and after completing these instructions you should go
+back to that page to complete configuration.
 
 ## Building from source
 
@@ -54,34 +49,6 @@ following the instructions at [rustup.rs](https://www.rustup.rs/).
 
 Finally, building the UI requires [yarn](https://yarnpkg.com/en/).
 
-You can continue to follow the build/install instructions below for a manual
-build and install, or alternatively you can run the prep script called `prep.sh`.
-
-    $ cd moonfire-nvr
-    $ ./prep.sh
-
-The script will take the following command line options, should you need them:
-
-* `-S`: Skip updating and installing dependencies through apt-get. This too can be
-        useful on repeated builds.
-
-You can edit variables at the start of the script to influence names and
-directories, but defaults should suffice in most cases. For details refer to
-the script itself. We will mention just one option, needed when you follow the
-suggestion to separate database and samples between flash storage and a hard disk.
-If you have the hard disk mounted on, lets say `/media/nvr`, and you want to
-store the video samples inside a directory named `samples` there, you would set:
-
-    SAMPLE_FILE_DIR=/media/nvr/samples
-
-The script will perform all necessary steps to leave you with a fully built,
-installed moonfire-nvr binary. The only thing
-you'll have to do manually is add your camera configuration(s) to the database.
-Alternatively, before running the script, you can create a file named `cameras.sql`
-in the same directory as the `prep.sh` script and it will be automatically
-included for you.
-For instructions, you can skip to "[Camera configuration and hard disk mounting](#camera)".
-
 Once prerequisites are installed, Moonfire NVR can be built as follows:
 
     $ yarn
@@ -92,74 +59,21 @@ Once prerequisites are installed, Moonfire NVR can be built as follows:
     $ sudo mkdir /usr/local/lib/moonfire-nvr
     $ sudo cp -R ui-dist /usr/local/lib/moonfire-nvr/ui
 
-## Further configuration
+## Creating the user and database
 
-Moonfire NVR should be run under a dedicated user. It keeps two kinds of
-state:
-
-   * a SQLite database, typically <1 GiB. It should be stored on flash if
-     available.
-   * the "sample file directory", which holds the actual samples/frames of
-     H.264 video. This should be quite large and typically is stored on a hard
-     drive.
-
-(See [schema.md](schema.md) for more information.)
-
-Both kinds of state are intended to be accessed only by Moonfire NVR itself.
-However, the interface for adding new cameras is not yet written, so you will
-have to manually insert cameras with the `sqlite3` command line tool prior to
-starting Moonfire NVR.
-
-Manual commands would look something like this:
+You can create Moonfire NVR's dedicated user and SQLite database with the
+following commands:
 
     $ sudo addgroup --system moonfire-nvr
     $ sudo adduser --system moonfire-nvr --home /var/lib/moonfire-nvr
     $ sudo mkdir /var/lib/moonfire-nvr
+    $ sudo chown moonfire-nvr:moonfire-nvr /var/lib/moonfire-nvr
     $ sudo -u moonfire-nvr -H mkdir db sample
     $ sudo -u moonfire-nvr moonfire-nvr init
 
-### <a name="cameras"></a>Camera configuration and hard drive mounting
+## System Service
 
-If a dedicated hard drive is available, set up the mount point:
-
-    $ sudo vim /etc/fstab
-    $ sudo mount /var/lib/moonfire-nvr/sample
-
-Once setup is complete, it is time to add camera configurations to the
-database. If the daemon is running, you will need to stop it temporarily:
-
-    $ sudo systemctl stop moonfire-nvr
-
-You can configure the system through a text-based user interface:
-
-    $ sudo -u moonfire-nvr moonfire-nvr config 2>debug-log
-
-In the user interface, add your cameras under the "Edit cameras" dialog.
-There's a "Test" button to verify your settings directly from the dialog.
-
-After the cameras look correct, go to "Edit retention" to assign disk space to
-each camera. Leave a little slack (at least 100 MB per camera) between the total
-limit and the filesystem capacity, even if you store nothing else on the disk.
-There are several reasons this is needed:
-
-   * The limit currently controls fully-written files only. There will be up
-     to two minutes of video per camera of additional video.
-   * The rotation happens after the limit is exceeded, not proactively.
-   * Moonfire NVR currently doesn't account for the unused space in the final
-     filesystem block at the end of each file.
-   * Moonfire NVR doesn't account for the space used for directory listings.
-   * If a file is open when it is deleted (such as if a HTTP client is
-     downloading it), it stays around until the file is closed. Moonfire NVR
-     currently doesn't account for this.
-
-When finished, start the daemon:
-
-    $ sudo systemctl start moonfire-nvr
-
-### System Service
-
-Moonfire NVR can be run as a systemd service. If you used `prep.sh` this has
-been done for you. If not, Create
+Moonfire NVR can be run as a systemd service. Create
 `/etc/systemd/system/moonfire-nvr.service`:
 
     [Unit]
@@ -188,14 +102,20 @@ been done for you. If not, Create
 Note that the HTTP port currently has no authentication, encryption, or
 logging; it should not be directly exposed to the Internet.
 
-Complete the installation through `systemctl` commands:
+Tell `systemd` to look for the new file:
 
     $ sudo systemctl daemon-reload
-    $ sudo systemctl start moonfire-nvr
-    $ sudo systemctl status moonfire-nvr
-    $ sudo systemctl enable moonfire-nvr
 
 See the [systemd](http://www.freedesktop.org/wiki/Software/systemd/)
 documentation for more information. The [manual
 pages](http://www.freedesktop.org/software/systemd/man/) for `systemd.service`
 and `systemctl` may be of particular interest.
+
+Don't enable or start the service just yet; you'll need to do some more
+configuration first.
+
+## Completing installation
+
+After the steps on this page, go back to [Downloading, installing, and
+configuring Moonfire NVR](install.md) to set up the sample file directory and
+configure the system.