examples: update var_service/README again
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/examples/var_service/README b/examples/var_service/README
index 52dd781..41106b5 100644
--- a/examples/var_service/README
+++ b/examples/var_service/README
@@ -40,8 +40,8 @@
process for an individual service. Service directories themselves sit
inside a containing directory, and the runsvdir program supervises that
directory, running one child runsv process for the service in each
-subdirectory. Out of the box on Debian, for example, an instance of
-runsvdir supervises services in subdirectories of /var/service/.
+subdirectory. A typical choice is to start an instance of runsvdir
+which supervises services in subdirectories of /var/service/.
If /var/service/log/ exists, runsv will supervise two services,
and will connect stdout of main service to the stdin of log service.
@@ -94,7 +94,7 @@
and in many cases you also want to babysit them.
They present a case where different services need to control (start, stop,
-restart) eact other.
+restart) each other.
var_service/dhcp_if
@@ -110,7 +110,9 @@
This is an example of service with has a "finish" script. If downed ("sv d"),
"finish" is executed. For this service, it removes DHCP address from
-the interface.
+the interface. This is useful when ifplugd detects that the the link is dead
+(cable is no longer attached anywhere) and downs us - keeping DHCP configured
+addresses on the interface would make kernel still try to use it.
var_service/zcip_if
@@ -138,6 +140,9 @@
var_service/fw
+"Firewall" script, although it is tasked with much more than setting up firewall.
+It is responsible for all aspects of network configuration.
+
This is an example of *one-shot* service.
It reconfigures network based on current known state of ALL interfaces.
@@ -147,7 +152,7 @@
One-shot-ness of this service means that it shuts itself off after single run.
IOW: it is not a constantly running daemon sort of thing.
It starts, it configures the network, it shuts down, all done
-(unlike infamous NetworkManagers which sit in RAM forever, doing hell knows what).
+(unlike infamous NetworkManagers which sit in RAM forever).
However, any dhcp/ppp/vpn or similar service can restart it anytime
when it senses the change in network configuration.
@@ -158,10 +163,13 @@
# Make ourself one-shot
sv o .
at the very beginning of fw/run script, not at the end.
+
Therefore, any "sv u /var/run/service/fw" command by any other
script "undoes" o(ne-shot) command if fw still runs, thus
runsv will rerun it; or start it in a normal way if fw is not running.
+This mechanism is the reason why fw is a service, not just a script.
+
System administrators are expected to edit fw/run script, since
network configuration needs are likely to be very complex and different
for non-trivial installations.