TCPSLICE(8)                                                        TCPSLICE(8)


       tcpslice - extract pieces of and/or glue together tcpdump files


       tcpslice [ -dRrt ] [ -w file ]
                [ start-time [ end-time ] ] file ...


       Tcpslice  is  a  program  for extracting 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’s -tt flag).  For example, 654321098.7654 specifies 38 sec-
       onds and 765,400 microseconds after 8:51PM PDT, Sept. 25, 1990.

       All examples in this manual are given for PDT times, but when  display-
       ing  times and interpreting times symbolically as discussed below, tcp-
       slice 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 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 as 90y9m25d20h51m38s765400u.

       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 spec-
       ified) 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  specify-
       ing 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  times-
       tamps of the first and last packets in each input file and exits.  Only
       one of these three options may be specified.

       -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.

       -w     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

       The current version is available in the ‘‘tcpslice’’ module of the  CVS
       tree at; see the 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  indi-
       cated  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.

       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: ‘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 par-
       tially present, typically due to tcpdump being ungracefully killed).

                               21 December 1996                    TCPSLICE(8)

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