add readme for the systemd service

Author: teleivo

README.md

@@ -66,6 +66,10 @@ diskmon -basedir <directory> -limit 65 \
 
 so that the credentials are not in your shell history.
 
+### Running as a service
+
+Read [Running diskmon as a service](./examples/README.md).
+
 ## Build from source
 
 You need to have [Go 1.16](https://golang.org) installed to build the binary yourself.

examples/README.md

@@ -0,0 +1,55 @@
+# Running diskmon as a service
+
+[systemd](https://systemd.io/)
+> systemd is a suite of basic building blocks for a Linux system. It provides a
+> system and service manager that runs as PID 1 and starts the rest of the
+> system.
+
+I provide a simple systemd [service file](./diskmon.service) that demonstrates
+how you might be able to run diskmon as a service using `systemd`. You will
+need to adjust paths to diskmon and mount points and flags to fit your
+environment and needs.
+
+## Installation
+
+Install the diskmon service
+
+```sh
+sudo cp ./examples/diskmon.service /etc/systemd/system/diskmon.service
+sudo chmod 664 /etc/systemd/system/diskmon.service
+```
+
+Adapt the service file to your needs!
+
+Start diskmon to see if systemd can start diskmon successfully
+
+```sh
+sudo systemctl start diskmon
+```
+
+Check the service status
+
+```sh
+sudo systemctl status diskmon
+```
+
+or the diskmon logs
+
+```sh
+sudo journalctl --follow --unit diskmon --boot
+```
+
+If all went well, enable diskmon to start automatically at boot
+
+```sh
+sudo systemctl enable diskmon
+```
+
+Reboot and check the status, logs again to see if all is well.
+
+## Limitations
+
+* have not yet figured out how to securly pass the Slack API token. You could
+  incorporate a subshell command that for example calls your password manager
+  to pass the token in. This way you would not add the token in plain text into
+  the service file which is readable by others on your system.