rc.d: document 'quiet' prefix and fix dhclient/devd interaction

Document the current semantics of the 'quiet' command prefix
in the rc.subr(8).

Fix dhclient rc.d script: it should not call err() for
non-DHCP-enabled interface when it is called from devd, because the
latter just blindly calls 'service dhclient quietstart' on each "link
up" event.

Since the 'quietstart' will silence the message "Cannot 'start' <foo>.
Set <foo>_enable to YES in /etc/rc.conf or use 'onestart' instead of
'start'." and running dhclient on the non-DHCP-enabled interface is
the same thing as running the service <foo> without <foo>_enable set,
such modification is in sync with the current semantics of the 'quiet'
prefix.

Approved by: glebius
Reviewed by: freebsd-rc list
MFC after:	2 weeks

1 files changed, 17 insertions, 1 deletions

diff --git a/share/man/man8/rc.subr.8 b/share/man/man8/rc.subr.8
index 9f6c7fa..a3c759a 100644
--- a/share/man/man8/rc.subr.8
+++ b/share/man/man8/rc.subr.8
@@ -339,7 +339,7 @@ with
 being the list of valid arguments
 prefixed by
 .Sm off
-.Dq Bq Li fast | force | one .
+.Dq Bq Li fast | force | one | quiet .
 .Sm on
 .It Ic reverse_list Ar item ...
 Print the list of
@@ -427,6 +427,22 @@ Skip the checks for
 being set to
 .Dq Li YES ,
 but performs all the other prerequisite tests.
+.It Li quiet
+Inhibits some verbose diagnostics.
+Currently, this includes messages
+.Qq Starting ${name}
+(as checked by
+.Ic check_startmsgs
+inside
+.Nm )
+and errors about usage of services that are not enabled in
+.Xr rc.conf 5 .
+This prefix also sets
+.Va rc_quiet Ns = Ns Li YES .
+.Em Please, note:
+.Va rc_quiet
+is not intended to completely mask all debug and warning messages,
+but only certain small classes of them.
 .El
 .Pp
 .Ic run_rc_command