Only support a single systemd credential by default (#930).

Reviewed-on: https://projects.torsion.org/borgmatic-collective/borgmatic/pulls/930
Reviewed-by: Dan Helfman <[email protected]>

docs/how-to/provide-your-passwords.md

@@ -39,27 +39,45 @@ Save your password as an encrypted credential to `/etc/credstore.encrypted/borgm
 # systemd-ask-password -n | systemd-creds encrypt - /etc/credstore.encrypted/borgmatic.pw
 ```
 
+Then uncomment or use the following in your configuration file:
+
+```yaml
+encryption_passcommand: "cat ${CREDENTIALS_DIRECTORY}/borgmatic.pw"
+```
+
 Note that the name `borgmatic.pw` is hardcoded in the systemd service file.
 
-If you use multiple different passwords, save them as encrypted credentials to `/etc/credstore.encrypted/borgmatic/`, e.g.,
+To use multiple different passwords, save them as encrypted credentials to `/etc/credstore.encrypted/borgmatic/`, e.g.,
 
 ```
 # mkdir /etc/credstore.encrypted/borgmatic
 # systemd-ask-password -n | systemd-creds encrypt --name=borgmatic_backupserver1 - /etc/credstore.encrypted/borgmatic/backupserver1
 # systemd-ask-password -n | systemd-creds encrypt --name=borgmatic_pw2 - /etc/credstore.encrypted/borgmatic/pw2
 ...
 ```
+
 Ensure that the file names, (e.g. `backupserver1`) match the corresponding part of
-the `--name` option *after* the underscore (_). The `borgmatic` folder is hardcoded in the systemd service file.
+the `--name` option *after* the underscore (_), and that the part *before* 
+the underscore matches the directory name (e.g. `borgmatic`).
 
-Then uncomment or use one of the following in your configuration file. Adjust `borgmatic_backupserver1`
-according to the name given to the credential.
+Then, uncomment the appropriate line in the systemd service file:
 
-```yaml
-encryption_passcommand: "cat ${CREDENTIALS_DIRECTORY}/borgmatic.pw"
+```
+# systemctl edit borgmatic.service
+...
+# Load multiple encrypted credentials.
+LoadCredentialEncrypted=borgmatic:/etc/credstore.encrypted/borgmatic/
+```
+
+Finally, use the following in your configuration file:
+
+```
 encryption_passcommand: "cat ${CREDENTIALS_DIRECTORY}/borgmatic_backupserver1"
 ```
 
+Adjust `borgmatic_backupserver1` according to the name given to the credential 
+and the directory set in the service file.
+
 ### Environment variable interpolation
 
 <span class="minilink minilink-addedin">New in version 1.6.4</span> borgmatic

sample/systemd/borgmatic.service

@@ -10,10 +10,12 @@ Documentation=https://torsion.org/borgmatic/
 [Service]
 Type=oneshot
 
-# Load encrypted credentials.
-LoadCredentialEncrypted=borgmatic:/etc/credstore.encrypted/borgmatic/
+# Load single encrypted credential.
 LoadCredentialEncrypted=borgmatic.pw
 
+# Load multiple encrypted credentials.
+# LoadCredentialEncrypted=borgmatic:/etc/credstore.encrypted/borgmatic/
+
 # Security settings for systemd running as root, optional but recommended to improve security. You
 # can disable individual settings if they cause problems for your use case. For more details, see
 # the systemd manual: https://www.freedesktop.org/software/systemd/man/systemd.exec.html