Describe service in README

README.md

@@ -1,2 +1,33 @@
 # dirtyboot
-Detect and log Linux reboot without clean shutdown
+
+Detect and log Linux boot not preceded by a clean shutdown.
+
+## Mechanism
+
+A systemd service, started early in the boot process, writes a marker file
+(`/var/lib/dirtyboot` by default).  When the service is stopped, during system
+shutdown, the marker file is removed.
+
+Thus, if the marker file is already present the next time the service starts,
+it means the system wasn't shut down cleanly before rebooting. Whenever this
+condition occurs, the service writes a corresponding warning to the system log.
+
+## Inspecting dirty reboot warnings
+
+Run the command
+
+    journalctl -t dirtyboot
+
+## Installation
+
+Put the systemd unit file in `/etc/systemd/system`, and the shell script to
+`/usr/sbin/dirtyboot`.  Then enable the service using
+
+    systemctl enable dirtyboot
+
+## Motivation
+
+I had an unstable system which tended to hang after long periods of idling.
+This simple tool was used to keep track of the number of hard resets I had to
+do to restore operation of a hung system.  Since system log entries are
+timestamped, it also records the time interval between such hard resets.