tcpslice - Unix, Linux Command
tcpslice - extract pieces of and/or glue together tcpdump files
-dRrt ] [
-w file ]
end-time ] ]
Tcpslice is a program for extracting portions of packet-trace files generated using
It can also be used to glue together several such files, as discussed
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
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 tcpdumps
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
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
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
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 fields 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
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
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
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.
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.
Dump the timestamps of the first and last packets in each input file
as raw timestamps (i.e., in the form sssssssss.uuuuuu).
-R except the timestamps are dumped in human-readable format, similar
to that used by date(1).
-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.
The original author was:
Vern Paxson, of
Lawrence Berkeley Laboratory, University of California, Berkeley, CA.
It is currently being maintained by tcpdump.org.
The current version is available in the tcpslice module of the CVS
tree at tcpdump.org; see the tcpdump.org home page at
for information on anonymous CVS access.
The original distribution is available via anonymous ftp:
Please send problems, bugs, questions, desirable enhancements, etc. to:
Please send source code contributions, etc. to:
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
tcpslice cannot read its input from stdin, since it uses random-access
to rummage through its input files.
tcpslice 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 users terminal.
Note that this means you must either redirect stdout or specify an
output file via -w.
tcpslice will not work properly on tcpdump 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: couldnt 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.
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
being ungracefully killed).