User-defined hooks for global setup or cleanup that run before/after all actions. (#192).

docs/how-to/add-preparation-and-cleanup-steps-to-backups.md

@@ -20,22 +20,47 @@ hooks:
         - rm /to/file.sql
 ```
 
-borgmatic hooks run once per configuration file. `before_backup` hooks run
-prior to backups of all repositories. `after_backup` hooks run afterwards, but
-not if an error occurs in a previous hook or in the backups themselves.
+The `before_backup` and `after_backup` hooks each run once per configuration
+file. `before_backup` hooks run prior to backups of all repositories in a
+configuration file, right before the `create` action. `after_backup` hooks run
+afterwards, but not if an error occurs in a previous hook or in the backups
+themselves.
 
+You can also use `before_everything` and `after_everything` hooks to perform
+global setup or cleanup:
+
+```yaml
+hooks:
+    before_everything:
+        - set-up-stuff-globally
+    after_everything:
+        - clean-up-stuff-globally
+```
+
+`before_everything` hooks collected from all borgmatic configuration files run
+once before all configuration files (prior to all actions), but only if there
+is a `create` action. An error encountered during a `before_everything` hook
+causes borgmatic to exit without creating backups.
+
+`after_everything` hooks run once after all configuration files and actions,
+but only if there is a `create` action. It runs even if an error occurs during
+a backup or a backup hook, but not if an error occurs during a
+`before_everything` hook.
 
 ## Error hooks
 
 borgmatic also runs `on_error` hooks if an error occurs, either when creating
-a backup or running another hook. Here's an example configuration:
+a backup or running a backup hook. Here's an example configuration:
 
 ```yaml
 hooks:
     on_error:
-        - echo "Error while creating a backup or running a hook."
+        - echo "Error while creating a backup or running a backup hook."
 ```
 
+Note however that borgmatic does not run `on_error` hooks if an error occurs
+within a `before_everything` or `after_everything` hook.
+
 ## Hook output
 
 Any output produced by your hooks shows up both at the console and in syslog
@@ -48,7 +73,8 @@ your backups</a>.
 An important security note about hooks: borgmatic executes all hook commands
 with the user permissions of borgmatic itself. So to prevent potential shell
 injection or privilege escalation, do not forget to set secure permissions
-(`chmod 0700`) on borgmatic configuration files and scripts invoked by hooks.
+on borgmatic configuration files (`chmod 0600`) and scripts (`chmod 0700`)
+invoked by hooks.
 
 
 ## Related documentation

docs/how-to/set-up-backups.md

@@ -7,11 +7,11 @@ To get up and running, first [install
 Borg](https://borgbackup.readthedocs.io/en/stable/installation.html), at
 least version 1.1.
 
-Borgmatic consumes configurations in `/etc/borgmatic/` and `/etc/borgmatic.d/`
-by default. Therefore, we show how to install borgmatic for the root user which
-will have access permissions for these locations by default.
+By default, borgmatic looks for its configuration files in `/etc/borgmatic/`
+and `/etc/borgmatic.d/`, where the root user typically has read access.
 
-Run the following commands to download and install borgmatic:
+So, to download and install borgmatic as the root user, run the following
+commands:
 
 ```bash
 sudo pip3 install --user --upgrade borgmatic
@@ -39,6 +39,7 @@ borgmatic:
  * [OpenBSD](http://ports.su/sysutils/borgmatic)
  * [openSUSE](https://software.opensuse.org/package/borgmatic)
  * [stand-alone binary](https://github.com/cmarquardt/borgmatic-binary)
+ * [virtualenv](https://virtualenv.pypa.io/en/stable/)
 
 
 ## Hosting providers