guardctrl.md

@@ -4,4 +4,17 @@ Guardian comes with `guardctrl`, which is an interface for controlling and super
 
 Each guardian node is handled by a systemd "unit", which describes how the process should be handled.  We use "templated" units, which is a common way to describe supervision for a set of common processes.
 
+## host setup
+
+The needed components are part of the `guardctrl` package (which is available through the [LIGO Debian apt archives](http://apt.ligo-wa.caltech.edu/debian/):
+```shell
+# apt install guardctrl
+```
+
+guardctrl assumes a systemd --user instance.  For the LIGO site installations we therefore create a `guardian` user:
+```shell
+# adduser --uid 1010 --ingroup controls --disabled-password guardian
+```
+We use `uid=1010` to not collide with any of the other standard system users, and we add it to the `controls` group so that it can write archive and channel info to locations owned by the controls group.
+
 /opt/rtcds/userapps/release/cds/h1/daqfiles/ini/H1EDCU_GRD.ini
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