Documentation for new logging control options

Documentation for '--console-leve' and '--log-level'.

doc/manpages/dinit.8.m4

@@ -99,7 +99,8 @@ The \fBdinit\fR daemon will simply exit rather than executing the \fB$$$SHUTDOWN
 .TP
 \fB\-q\fR, \fB\-\-quiet\fR
 Run with no output to the terminal/console.
-This disables service status messages and sets the log level for the console log to \fBNONE\fR.
+This disables service status messages and sets the log level for the console log to \fBnone\fR.
+To re-enable (some) output, use the \fB\-\-console\-level\fR option after this option.
 .TP
 \fB\-b\fR \fIpath\fR, \fB\-\-cgroup\-path\fR \fIpath\fR
 Specify the path to resolve relative cgroup paths against.
@@ -123,6 +124,19 @@ be started.
 \fBNote:\fR on Linux, if \fBdinit\fR is running as PID 1 and with UID 0, it may ignore "naked"
 service names (without preceding \fB\-\-service\fR/\fB\-t\fR) provided on the command line.
 See the \fBCOMMAND LINE FROM KERNEL\fR section.
+.TP
+\fB\-\-console\-level\fR \fIlevel\fR
+Specify the minimum log level of messages that should be logged to the console.
+From highest to lowest, the levels are \fBerror\fR, \fBwarn\fR, \fBinfo\fR and \fBdebug\fR.
+Use a level of \fBnone\fR to suppress all messages.
+Note that unless \fB\-\-quiet\fR (\fB\-q\fR) is also specified, service state change messages
+(service started, stopped etc) are always output.
+.TP
+\fB\-\-log\-level\fR \fIlevel\fR
+Specify the minimum log level of messages that should be sent to the primary log (syslog facility
+or file).
+From highest to lowest, the levels are \fBerror\fR, \fBwarn\fR, \fBinfo\fR and \fBdebug\fR.
+Use a level of \fBnone\fR to suppress all messages.
 .\"
 .SH SERVICE DESCRIPTION FILES
 .\"
@@ -198,6 +212,26 @@ System shutdown or restart need to be handled by the primary \fBinit\fR, which s
 \fBdinit\fR on normal startup, and terminate \fBdinit\fR before shutdown, by signalling it and
 waiting for it to terminate after stopping services (possibly by invoking \fBdinitctl shutdown\fR).
 .\"
+.SH LOGGING
+Dinit "logs" via two mechanisms simultaneously: the "console" (standard output, not necessarily associated
+with an actual console if \fBdinit\fR was started with output directed elsewhere) and the "main log facility"
+which is the syslog facility by default but which may be directed to a file.
+
+Various options are available to control the types and "levels" of message that will be sent to each facility,
+and the destination of the main facility.
+The levels available (from low to high) are \fBdebug\fR, \fBnotice\fR, \fBwarn\fR, and \fBerror\fR.
+Selecting a particular log level for facility will cause the facility to receive messages of that level and higher.
+The special level \fBnone\fR inhibits a facility from receiving any messages.
+
+Service status messages (service started or stopped) have a nominal level of \fBnotice\fR, except for failure
+which has a level of \fBerror\fR or \fBwarn\fR in case of transitive failure (due to a dependency).
+These messages are, by default, always issued to the console regardless of level, unless the \fB\-\-quiet\fR
+(\fB\-q\fR) option has been used.
+
+To debug boot issues it may be useful to use \fB\-q\fR (which also sets the level to \fBnone\fR) and then
+also reset the level via the \fB\-\-console\-level\fR option to either \fBwarn\fR or \fBerror\fR.
+This will reduce noise in the output from successful service startup.
+.\"
 .SH COMMAND LINE FROM KERNEL
 .LP
 When running as PID 1, \fBdinit\fR may process the command line differently, to compensate for kernel behaviour.