tcpslice -- extract pieces of and/or glue together tcpdump files
tcpslice [-dRrt] [-w file] [start-time [end-time]] file ...
The tcpslice utility extracts portions of packet-trace files generated
using tcpdump(1)'s -w flag. It can also be used to glue together several
such files, as discussed below.
The basic operation of tcpslice is to copy to stdout all packets from its
input file(s) whose timestamps fall within a given range. The starting
and ending times of the range may be specified on the command line. All
ranges are inclusive. The starting time defaults to the time of the
first packet in the first input file; we call this the first time. The
ending time defaults to ten years after the starting time. Thus, the
command tcpslice trace-file simply copies trace-file to stdout (assuming
the file does not include more than ten years' worth of data).
There are a number of ways to specify times. The first is using Unix
timestamps of the form sssssssss.uuuuuu (this is the format specified by
tcpdump(1)'s -tt flag). For example, 654321098.7654 specifies 38 seconds
and 765,400 microseconds after 8:51PM PDT, Sept. 25, 1990.
All examples in this manual are given for PDT times, but when displaying
times and interpreting times symbolically as discussed below, tcpslice
uses the local timezone, regardless of the timezone in which the
tcpdump(1) file was generated. The daylight-savings setting used is that
which is appropriate for the local timezone at the date in question. For
example, times associated with summer months will usually include daylight-savings
effects, and those with winter months will not.
Times may also be specified relative to either the first time (when specifying
a starting time) or the starting time (when specifying an ending
time) by preceding a numeric value in seconds with a `+'. For example, a
starting time of +200 indicates 200 seconds after the first time, and the
two arguments +200 +300 indicate from 200 seconds after the first time
through 500 seconds after the first time.
Times may also be specified in terms of years (y), months (m), days (d),
hours (h), minutes (m), seconds (s), and microseconds(u). For example,
the Unix timestamp 654321098.7654 discussed above could also be expressed
When specifying times using this style, fields that are omitted default
as follows. If the omitted field is a unit greater than that of the
first specified field, then its value defaults to the corresponding value
taken from either first time (if the starting time is being specified) or
the starting time (if the ending time is being specified). If the omitted
field is a unit less than that of the first specified field, then it
defaults to zero. For example, suppose that the input file has a first
time of the Unix timestamp mentioned above, i.e., 38 seconds and 765,400
microseconds after 8:51PM PDT, Sept. 25, 1990. To specify 9:36PM PDT
(exactly) on the same date we could use 21h36m. To specify a range from
9:36PM PDT through 1:54AM PDT the next day we could use 21h36m 26d1h54m.
Relative times can also be specified when using the ymdhmsu format.
Omitted fields then default to 0 if the unit of the field is greater than
that of the first specified field, and to the corresponding value taken
from either the first time or the starting time if the omitted field's
unit is less than that of the first specified field. Given a first time
of the Unix timestamp mentioned above, 22h +1h10m specifies a range from
10:00PM PDT on that date through 11:10PM PDT, and +1h +1h10m specifies a
range from 38.7654 seconds after 9:51PM PDT through 38.7654 seconds after
11:01PM PDT. The first hour of the file could be extracted using +0 +1h.
Note that with the ymdhmsu format there is an ambiguity between using m
for `month' or for `minute'. The ambiguity is resolved as follows: if an
m field is followed by a d field then it is interpreted as specifying
months; otherwise it specifies minutes.
If more than one input file is specified then tcpslice first copies packets
lying in the given range from the first file; it then increases the
starting time of the range to lie just beyond the timestamp of the last
packet in the first file, repeats the process with the second file, and
so on. Thus files with interleaved packets are not merged. For a given
file, only packets that are newer than any in the preceding files will be
considered. This mechanism avoids any possibility of a packet occurring
more than once in the output.
If any of -R, -r or -t are specified then tcpslice reports the timestamps
of the first and last packets in each input file and exits. Only one of
these three options may be specified.
The following options are available:
-d Dump the start and end times specified by the given range and
exit. This option is useful for checking that the given range
actually specifies the times you think it does. If one of -R, -r
or -t has been specified then the times are dumped in the corresponding
format; otherwise, raw format (-R) is used.
-R Dump the timestamps of the first and last packets in each input
file as raw timestamps (i.e., in the form sssssssss.uuuuuu).
-r Same as -R except the timestamps are dumped in human-readable
format, similar to that used by date(1).
-t Same as -R except the timestamps are dumped in tcpslice format,
i.e., in the ymdhmsu format discussed above.
Direct the output to file rather than stdout.
Vern Paxson <email@example.com>, of Lawrence Berkeley Laboratory, University
of California, Berkeley, CA.
An input filename that beings with a digit or a `+' can be confused with
a start/end time. Such filenames can be specified with a leading `./';
for example, specify the file `04Jul76.trace' as `./04Jul76.trace'.
The tcpslice utility cannot read its input from stdin, since it uses random-access
to rummage through its input files.
The tcpslice utility refuses to write to its output if it is a terminal
(as indicated by isatty(3)). This is not a bug but a feature, to prevent
it from spraying binary data to the user's terminal. Note that this
means you must either redirect stdout or specify an output file via -w.
The tcpslice utility will not work properly on tcpdump(1) files spanning
more than one year; with files containing portions of packets whose original
length was more than 65,535 bytes; nor with files containing fewer
than three packets. Such files result in the error message: `couldn't
find final packet in file'. These problems are due to the interpolation
scheme used by tcpslice to greatly speed up its processing when dealing
with large trace files. Note that tcpslice can efficiently extract
slices from the middle of trace files of any size, and can also work with
truncated trace files (i.e., the final packet in the file is only partially
present, typically due to tcpdump(1) being ungracefully killed).
FreeBSD 5.2.1 October 14, 1991 FreeBSD 5.2.1 [ Back ]