systemd: update with details of new startmin target
The obmc-host-startmin@.target was introduced quite some time ago.
Update the documentation with the details on it.
Signed-off-by: Andrew Geissler <geissonator@yahoo.com>
Change-Id: I04141b06cbc43475754f05730e5de246162fb5e5
diff --git a/architecture/openbmc-systemd.md b/architecture/openbmc-systemd.md
index 722ec1c..c7123d9 100644
--- a/architecture/openbmc-systemd.md
+++ b/architecture/openbmc-systemd.md
@@ -36,27 +36,46 @@
When OpenBMC is used within a server, the [obmc-host-start@.target](https://github.com/openbmc/phosphor-state-manager/blob/master/target_files/obmc-host-start%40.target)
is what drives the boot of the system.
+To start it you would run `systemctl start obmc-host-start@0.target`.
+
If you dig into its .requires relationship, you'll see the following in the file
system
```
-ls -1 /lib/systemd/system/obmc-host-start@0.target.requires
+ls -1 /lib/systemd/system/obmc-host-start@0.target.requires/
+obmc-host-startmin@0.target
+phosphor-reset-host-reboot-attempts@0.service
+```
+The [obmc-host-startmin@.target](https://github.com/openbmc/phosphor-state-manager/blob/master/target_files/obmc-host-startmin%40.target)
+represents the bare minimum of services and targets required to start the host.
+This target is also utilized in host reboot scenarios. This distinction of a
+host-start and a host-startmin target allows the user to put services in the
+`obmc-host-start@.target` that should only be run on an initial host boot (and
+not run on host reboots). For example, in the output above you can see the user
+only wants to run the `phosphor-reset-host-reboot-attempts@0.service` on a fresh
+host boot attempt.
+
+Next if we look at the `obmc-host-startmin@0.target`, we see this:
+```
+ls -1 /lib/systemd/system/obmc-host-startmin@0.target.requires/
obmc-chassis-poweron@0.target
start_host@0.service
```
-You can see we have another target in here, obmc-chassis-poweron@0.target,
-along with a service that will all be started by systemd when you do a
-"systemctl start obmc-host-start@0.target".
+You can see within `obmc-host-startmin@0.target` that we have another target in
+there, `obmc-chassis-poweron@0.target`, along with a service aptly named
+`start_host@0.service`.
-The target has corresponding services associated with it:
+The `obmc-chassis-poweron@0.target` has corresponding services associated with
+it:
```
-ls -1 /lib/systemd/system/obmc-chassis-poweron\@0.target.requires/
+ls -1 /lib/systemd/system/obmc-chassis-poweron@0.target.requires/
op-power-start@0.service
op-wait-power-on@0.service
```
-So basically, if you run `systemctl start obmc-host-start@0.target` then
-systemd will start execution of all associated services.
+
+If you run `systemctl start obmc-host-start@0.target` then systemd will start
+execution of all of the above associated target and services.
The services have dependencies within them that control the execution of each
service (for example, the op-power-start.service will run prior to the