docs: add --time-format option and ISO-8601 format to manual

Signed-off-by: Sami Kerola <kerolasa@iki.fi>

diff --git a/sys-utils/dmesg.1 b/sys-utils/dmesg.1
index c0606884af6b402a8ed759d966ef94bb9f3c1299..ce186d84e7cb6debff55a3b732298d34611b39e1 100644 (file)
--- a/sys-utils/dmesg.1
+++ b/sys-utils/dmesg.1
@@ -153,6 +153,28 @@ Wait for new messages. This feature is supported on systems with readable
 /dev/kmsg only (since kernel 3.5.0).
 .IP "\fB\-x\fR, \fB\-\-decode\fR"
 Decode facility and level (priority) number to human readable prefixes.
+.IP "\fB\-\-time\-format\fR \fIformat\fR"
+Print time stam using format
+.IR ctime ,
+.IR delta ,
+.I reltime
+or
+.IR iso .
+The three first time formats are aliases of time format specific options.
+The
+.I iso
+is a
+.B dmesg
+implementation of ISO-8601 timestamp format.  Purpose of this format is
+to make comparing of timestamps in between two system, and other parsing,
+easy.  The defition of timestamp is YYYY-MM-DD<T stands for date and time
+separator>HH:MM:SS,<microseconds><-+><GMT-0 timezone offset>.
+.IP
+The
+.I iso
+time format has the same issue as
+.IR ctime ,
+the time may be inaccurate if a system is suspended and resumed.
 .SH SEE ALSO
 .BR syslogd (8)
 .SH AUTHORS