X-Git-Url: https://git.tcpdump.org/tcpdump/blobdiff_plain/16a592dcadb25d2262d64f3811cb2da5e42e1846..486704db7c840dcfb51f70f1812d9c3ad37ad39c:/tcpdump.1.in

diff --git a/tcpdump.1.in b/tcpdump.1.in
index a9664692..ebf50ab6 100644
--- a/tcpdump.1.in
+++ b/tcpdump.1.in
@@ -128,6 +128,10 @@ tcpdump \- dump traffic on a network
 [
 .BI \-\-time\-stamp\-precision= tstamp_precision
 ]
+.ti +8
+[
+.B \-\-immediate\-mode
+]
 [
 .B \-\-version
 ]
@@ -140,7 +144,9 @@ tcpdump \- dump traffic on a network
 .SH DESCRIPTION
 .LP
 \fITcpdump\fP prints out a description of the contents of packets on a
-network interface that match the boolean \fIexpression\fP.  It can also
+network interface that match the boolean \fIexpression\fP; the
+description is preceded by a time stamp, printed, by default, as hours,
+minutes, seconds, and fractions of a second since midnight.  It can also
 be run with the
 .B \-w
 flag, which causes it to save the packet data to a file for later
@@ -204,7 +210,9 @@ your ``status'' character, typically control-T, although on some
 platforms, such as Mac OS X, the ``status'' character is not set by
 default, so you must set it with
 .BR stty (1)
-in order to use it) and will continue capturing packets.
+in order to use it) and will continue capturing packets. On platforms that
+do not support the SIGINFO signal, the same can be achieved by using the
+SIGUSR1 signal.
 .LP
 Reading packets from a network interface may require that you have
 special privileges; see the
@@ -419,6 +427,13 @@ monitor mode will be shown; if
 is specified, only those link-layer types available when in monitor mode
 will be shown.
 .TP
+.BI \-\-immediate\-mode
+Capture in "immediate mode".  In this mode, packets are delivered to
+tcpdump as soon as they arrive, rather than being buffered for
+efficiency.  This is the default when printing packets rather than
+saving packets to a ``savefile'' if the packets are being printed to a
+terminal rather than to a file or pipe.
+.TP
 .BI \-j " tstamp_type"
 .PD 0
 .TP
@@ -655,14 +670,16 @@ an encapsulated PGM packet.
 \fIDon't\fP print a timestamp on each dump line.
 .TP
 .B \-tt
-Print an unformatted timestamp on each dump line.
+Print the timestamp, as seconds since January 1, 1970, 00:00:00, UTC, and
+fractions of a second since that time, on each dump line.
 .TP
 .B \-ttt
 Print a delta (micro-second resolution) between current and previous line
 on each dump line.
 .TP
 .B \-tttt
-Print a timestamp in default format proceeded by date on each dump line.
+Print a timestamp, as hours, minutes, seconds, and fractions of a second
+since midnight, preceded by the date, on each dump line.
 .TP
 .B \-ttttt
 Print a delta (micro-second resolution) between current and first line
@@ -1865,11 +1882,15 @@ is the current clock time in the form
 .fi
 .RE
 and is as accurate as the kernel's clock.
-The timestamp reflects the time the kernel first saw the packet.
-No attempt
-is made to account for the time lag between when the
-Ethernet interface removed the packet from the wire and when the kernel
-serviced the `new packet' interrupt.
+The timestamp reflects the time the kernel applied a time stamp to the packet.
+No attempt is made to account for the time lag between when the network
+interface finished receiving the packet from the network and when the
+kernel applied a time stamp to the packet; that time lag could include a
+delay between the time when the network interface finished receiving a
+packet from the network and the time when an interrupt was delivered to
+the kernel to get it to read the packet and a delay between the time
+when the kernel serviced the `new packet' interrupt and the time when it
+applied a time stamp to the packet.
 .SH "SEE ALSO"
 stty(1), pcap(3PCAP), bpf(4), nit(4P), pcap-savefile(@MAN_FILE_FORMATS@),
 pcap-filter(@MAN_MISC_INFO@), pcap-tstamp(@MAN_MISC_INFO@)