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pcap(3)                                                        pcap(3)




NAME

       pcap - Packet Capture library


SYNOPSIS

       #include <pcap/pcap.h>



DESCRIPTION

       The  Packet  Capture  library provides a high level interface to packet
       capture systems. All packets on the network, even  those  destined  for
       other  hosts,  are accessible through this mechanism.  It also supports
       saving captured packets to a ``savefile'', and reading packets  from  a
       ``savefile''.

   Initializing
       pcap_init()  initializes  the  library.   It  takes  an argument giving
       options; currently, the options are:

       PCAP_CHAR_ENC_LOCAL
              Treat all strings supplied as arguments, and return all  strings
              to the caller, as being in the local character encoding.

       PCAP_CHAR_ENC_UTF_8
              Treat  all strings supplied as arguments, and return all strings
              to the caller, as being in UTF-8.

       On UNIX-like systems, the local character encoding  is  assumed  to  be
       UTF-8, so no character encoding transformations are done.

       On Windows, the local character encoding is the local ANSI code page.

       If  pcap_init()  is  called,  the  deprecated  pcap_lookupdev() routine
       always fails, so it should not be used, and, on Windows,  pcap_create()
       does not attempt to handle UTF-16LE strings.

       If pcap_init() is not called, strings are treated as being in the local
       ANSI code page on Windows, pcap_lookupdev() will succeed if there is  a
       device on which to capture, and pcap_create() makes an attempt to check
       whether the string passed as an argument is a UTF-16LE  string  -  note
       that this attempt is unsafe, as it may run past the end of the string -
       to handle pcap_lookupdev() returning a UTF-16LE string.  Programs  that
       don't  call  pcap_init()  should,  on Windows, call pcap_wsockinit() to
       initialize Winsock; this is not necessary if pcap_init() is called,  as
       pcap_init() will initialize Winsock itself on Windows.

       Routines

              pcap_init(3)
                     initialize the library

   Opening a capture handle for reading
       To  open  a handle for a live capture, given the name of the network or
       other interface on which the capture should  be  done,  call  pcap_cre-
       ate(),  set the appropriate options on the handle, and then activate it
       with pcap_activate().  If pcap_activate() fails, the handle  should  be
       closed with pcap_close().

       To obtain a list of devices that can be opened for a live capture, call
       pcap_findalldevs(); to free the list  returned  by  pcap_findalldevs(),
       call pcap_freealldevs().  pcap_lookupdev() will return the first device
       on that list that is not a ``loopback`` network interface.

       To open a handle for a ``savefile'' from which to read  packets,  given
       the pathname of the ``savefile'', call pcap_open_offline(); to set up a
       handle for a ``savefile'', given a FILE * referring to a  file  already
       opened for reading, call pcap_fopen_offline().

       In  order  to  get a ``fake'' pcap_t for use in routines that require a
       pcap_t as an argument, such as routines  to  open  a  ``savefile''  for
       writing and to compile a filter expression, call pcap_open_dead().

       pcap_create(),     pcap_open_offline(),    pcap_fopen_offline(),    and
       pcap_open_dead() return a pointer to a pcap_t, which is the handle used
       for  reading  packets  from the capture stream or the ``savefile'', and
       for finding out information about the capture stream  or  ``savefile''.
       To close a handle, use pcap_close().

       The options that can be set on a capture handle include

       snapshot length
              If,  when  capturing,  you  capture  the  entire contents of the
              packet, that requires more CPU time to copy the packet  to  your
              application,  more  disk and possibly network bandwidth to write
              the packet data to a file, and  more  disk  space  to  save  the
              packet.   If  you don't need the entire contents of the packet -
              for example, if you are only interested in the  TCP  headers  of
              packets  -  you can set the "snapshot length" for the capture to
              an appropriate value.  If the snapshot length is set to snaplen,
              and  snaplen is less than the size of a packet that is captured,
              only the first snaplen bytes of that packet will be captured and
              provided as packet data.

              A  snapshot length of 65535 should be sufficient, on most if not
              all networks, to capture all the data available from the packet.

              The snapshot length is set with pcap_set_snaplen().

       promiscuous mode
              On  broadcast  LANs  such  as  Ethernet,  if  the  network isn't
              switched, or if the adapter is connected to a "mirror port" on a
              switch to which all packets passing through the switch are sent,
              a network adapter receives all packets  on  the  LAN,  including
              unicast  or multicast packets not sent to a network address that
              the network adapter isn't configured to recognize.

              Normally, the adapter will discard those packets; however,  many
              network  adapters support "promiscuous mode", which is a mode in
              which all packets, even if they are not sent to an address  that
              the  adapter recognizes, are provided to the host.  This is use-
              ful for passively capturing traffic between two  or  more  other
              hosts for analysis.

              Note  that even if an application does not set promiscuous mode,
              the adapter could well be in promiscuous  mode  for  some  other
              reason.

              For  now,  this doesn't work on the "any" device; if an argument
              of "any" or NULL is supplied, the setting of promiscuous mode is
              ignored.

              Promiscuous mode is set with pcap_set_promisc().

       monitor mode
              On IEEE 802.11 wireless LANs, even if an adapter is in promiscu-
              ous mode, it will supply to the host only frames for the network
              with  which  it's  associated.   It  might also supply only data
              frames, not management or control frames, and might not  provide
              the  802.11  header or radio information pseudo-header for those
              frames.

              In "monitor mode",  sometimes  also  called  "rfmon  mode"  (for
              "Radio  Frequency  MONitor"), the adapter will supply all frames
              that it receives,  with  802.11  headers,  and  might  supply  a
              pseudo-header with radio information about the frame as well.

              Note  that  in  monitor mode the adapter might disassociate from
              the network with which it's associated, so that you will not  be
              able to use any wireless networks with that adapter.  This could
              prevent accessing files on a network server, or  resolving  host
              names or network addresses, if you are capturing in monitor mode
              and are not connected to another network with another adapter.

              Monitor    mode    is    set    with    pcap_set_rfmon(),    and
              pcap_can_set_rfmon() can be used to determine whether an adapter
              can be put into monitor mode.

       packet buffer timeout
              If, when capturing,  packets  are  delivered  as  soon  as  they
              arrive,  the  application capturing the packets will be woken up
              for each packet as it arrives, and might have  to  make  one  or
              more calls to the operating system to fetch each packet.

              If,  instead,  packets are not delivered as soon as they arrive,
              but are delivered after a short delay (called a  "packet  buffer
              timeout"),  more  than  one packet can be accumulated before the
              packets are delivered, so that a single wakeup would be done for
              multiple  packets,  and  each set of calls made to the operating
              system would supply  multiple  packets,  rather  than  a  single
              packet.  This reduces the per-packet CPU overhead if packets are
              arriving at a high rate, increasing the number  of  packets  per
              second that can be captured.

              The  packet  buffer  timeout  is required so that an application
              won't wait for the operating system's capture buffer to fill  up
              before  packets  are  delivered; if packets are arriving slowly,
              that wait could take an arbitrarily long period of time.

              Not all platforms support a packet buffer timeout; on  platforms
              that  don't, the packet buffer timeout is ignored.  A zero value
              for the timeout, on platforms that support a packet buffer time-
              out,  will  cause a read to wait forever to allow enough packets
              to arrive, with no timeout.  A negative value  is  invalid;  the
              result  of  setting  the  timeout  to a negative value is unpre-
              dictable.

              NOTE: the packet buffer timeout cannot be used  to  cause  calls
              that  read  packets  to  return within a limited period of time,
              because, on some platforms, the packet buffer timeout isn't sup-
              ported,  and,  on other platforms, the timer doesn't start until
              at least one packet arrives.  This means that the packet  buffer
              timeout  should  NOT  be  used,  for  example, in an interactive
              application to allow the packet capture  loop  to  ``poll''  for
              user  input  periodically,  as  there's no guarantee that a call
              reading packets will return after the timeout expires even if no
              packets have arrived.

              The packet buffer timeout is set with pcap_set_timeout().

       immediate mode
              In  immediate mode, packets are always delivered as soon as they
              arrive,  with  no  buffering.   Immediate  mode  is   set   with
              pcap_set_immediate_mode().

       buffer size
              Packets  that  arrive  for  a capture are stored in a buffer, so
              that they do not have to be read by the application as  soon  as
              they arrive.  On some platforms, the buffer's size can be set; a
              size that's too small could mean that, if too many  packets  are
              being  captured and the snapshot length doesn't limit the amount
              of data that's buffered, packets could be dropped if the  buffer
              fills  up before the application can read packets from it, while
              a size that's too large could use  more  non-pageable  operating
              system  memory  than  is necessary to prevent packets from being
              dropped.

              The buffer size is set with pcap_set_buffer_size().

       timestamp type
              On some platforms, the time stamp given to packets on live  cap-
              tures  can  come  from different sources that can have different
              resolutions or that can have different relationships to the time
              values  for  the current time supplied by routines on the native
              operating system.  See pcap-tstamp(7) for a list of  time  stamp
              types.

              The time stamp type is set with pcap_set_tstamp_type().

       Reading packets from a network interface may require that you have spe-
       cial privileges:

       Under SunOS 3.x or 4.x with NIT or BPF:
              You must have read access to /dev/nit or /dev/bpf*.

       Under Solaris with DLPI:
              You must have read/write access to the  network  pseudo  device,
              e.g.   /dev/le.   On at least some versions of Solaris, however,
              this is not sufficient to allow tcpdump to capture in  promiscu-
              ous mode; on those versions of Solaris, you must be root, or the
              application capturing packets must be installed setuid to  root,
              in  order  to  capture  in promiscuous mode.  Note that, on many
              (perhaps all) interfaces, if you don't  capture  in  promiscuous
              mode,  you  will  not see any outgoing packets, so a capture not
              done in promiscuous mode may not be very useful.

              In newer versions of Solaris,  you  must  have  been  given  the
              net_rawaccess  privilege;  this is both necessary and sufficient
              to give you access to the network pseudo-device -  there  is  no
              need  to  change  the  privileges on that device.  A user can be
              given that privilege by, for example, adding that  privilege  to
              the user's defaultpriv key with the usermod(8) command.

       Under HP-UX with DLPI:
              You  must  be  root or the application capturing packets must be
              installed setuid to root.

       Under IRIX with snoop:
              You must be root or the application capturing  packets  must  be
              installed setuid to root.

       Under Linux:
              You  must  be  root or the application capturing packets must be
              installed setuid to root, unless your distribution has a  kernel
              that  supports  capability  bits such as CAP_NET_RAW and code to
              allow those capability bits to be given to  particular  accounts
              and  to cause those bits to be set on a user's initial processes
              when they log in, in which case you  must  have  CAP_NET_RAW  in
              order to capture.

       Under ULTRIX and Digital UNIX/Tru64 UNIX:
              Any  user  may  capture  network traffic.  However, no user (not
              even the super-user) can  capture  in  promiscuous  mode  on  an
              interface  unless  the  super-user  has enabled promiscuous-mode
              operation on that interface using pfconfig(8), and no user  (not
              even  the super-user) can capture unicast traffic received by or
              sent by the machine on an interface unless  the  super-user  has
              enabled  copy-all-mode  operation on that interface using pfcon-
              fig, so useful packet capture on an interface probably  requires
              that either promiscuous-mode or copy-all-mode operation, or both
              modes of operation, be enabled on that interface.

       Under BSD (this includes macOS):
              You must have read access to /dev/bpf*  on  systems  that  don't
              have  a  cloning  BPF device, or to /dev/bpf on systems that do.
              On BSDs with a devfs (this includes macOS), this  might  involve
              more  than  just  having somebody with super-user access setting
              the ownership or permissions on  the  BPF  devices  -  it  might
              involve  configuring  devfs  to set the ownership or permissions
              every time the system is booted, if  the  system  even  supports
              that;  if  it  doesn't support that, you might have to find some
              other way to make that happen at boot time.

       Reading a saved packet file doesn't require special privileges.

       The packets read from the handle may include a  ``pseudo-header''  con-
       taining  various  forms  of  packet  meta-data, and probably includes a
       link-layer header whose  contents  can  differ  for  different  network
       interfaces.   To  determine  the  format of the packets supplied by the
       handle,  call  pcap_datalink();  https://www.tcpdump.org/linktypes.html
       lists  the values it returns and describes the packet formats that cor-
       respond to those values.

       Do NOT assume that the packets for a given capture or ``savefile`` will
       have any given link-layer header type, such as DLT_EN10MB for Ethernet.
       For example, the "any" device on Linux will have  a  link-layer  header
       type of DLT_LINUX_SLL or DLT_LINUX_SLL2 even if all devices on the sys-
       tem at the time the "any" device is opened have some  other  data  link
       type, such as DLT_EN10MB for Ethernet.

       To  obtain  the  FILE *  corresponding to a pcap_t opened for a ``save-
       file'', call pcap_file().

       Routines

              pcap_create(3)
                     get a pcap_t for live capture

              pcap_activate(3)
                     activate a pcap_t for live capture

              pcap_findalldevs(3)
                     get a list of devices that can be opened for a live  cap-
                     ture

              pcap_freealldevs(3)
                     free list of devices

              pcap_lookupdev(3)
                     get first non-loopback device on that list

              pcap_open_offline(3)
                     open a pcap_t for a ``savefile'', given a pathname

              pcap_open_offline_with_tstamp_precision(3)
                     open  a  pcap_t for a ``savefile'', given a pathname, and
                     specify the precision to provide for packet time stamps

              pcap_fopen_offline(3)
                     open a pcap_t for a ``savefile'', given a FILE *

              pcap_fopen_offline_with_tstamp_precision(3)
                     open a pcap_t for a ``savefile'',  given  a  FILE *,  and
                     specify the precision to provide for packet time stamps

              pcap_open_dead(3)
                     create a ``fake'' pcap_t

              pcap_close(3)
                     close a pcap_t

              pcap_set_snaplen(3)
                     set  the  snapshot  length for a not-yet-activated pcap_t
                     for live capture

              pcap_snapshot(3)
                     get the snapshot length for a pcap_t

              pcap_set_promisc(3)
                     set promiscuous mode for a not-yet-activated  pcap_t  for
                     live capture

              pcap_set_protocol_linux(3)
                     set  capture  protocol for a not-yet-activated pcap_t for
                     live capture (Linux only)

              pcap_set_rfmon(3)
                     set monitor mode for a not-yet-activated pcap_t for  live
                     capture

              pcap_can_set_rfmon(3)
                     determine  whether  monitor  mode can be set for a pcap_t
                     for live capture

              pcap_set_timeout(3)
                     set packet buffer timeout for a not-yet-activated  pcap_t
                     for live capture

              pcap_set_immediate_mode(3)
                     set  immediate  mode  for  a not-yet-activated pcap_t for
                     live capture

              pcap_set_buffer_size(3)
                     set buffer size for a not-yet-activated pcap_t  for  live
                     capture

              pcap_set_tstamp_type(3)
                     set  time  stamp  type for a not-yet-activated pcap_t for
                     live capture

              pcap_list_tstamp_types(3)
                     get list of available time stamp  types  for  a  not-yet-
                     activated pcap_t for live capture

              pcap_free_tstamp_types(3)
                     free list of available time stamp types

              pcap_tstamp_type_val_to_name(3)
                     get name for a time stamp type

              pcap_tstamp_type_val_to_description(3)
                     get description for a time stamp type

              pcap_tstamp_type_name_to_val(3)
                     get time stamp type corresponding to a name

              pcap_set_tstamp_precision(3)
                     set  time  stamp precision for a not-yet-activated pcap_t
                     for live capture

              pcap_get_tstamp_precision(3)
                     get the time stamp precision of a pcap_t for live capture

              pcap_datalink(3)
                     get link-layer header type for a pcap_t

              pcap_file(3)
                     get the FILE * for a pcap_t opened for a ``savefile''

              pcap_is_swapped(3)
                     determine  whether  a ``savefile'' being read came from a
                     machine with the opposite byte order

              pcap_major_version(3)
              pcap_minor_version(3)
                     get the major and minor version of the file  format  ver-
                     sion for a ``savefile''

   Selecting a link-layer header type for a live capture
       Some  devices  may  provide  more  than one link-layer header type.  To
       obtain a list of all link-layer header types provided by a device, call
       pcap_list_datalinks() on an activated pcap_t for the device.  To free a
       list of link-layer header types, call  pcap_free_datalinks().   To  set
       the  link-layer  header  type  for  a device, call pcap_set_datalink().
       This should be done after the device has been activated but before  any
       packets are read and before any filters are compiled or installed.

       Routines

              pcap_list_datalinks(3)
                     get a list of link-layer header types for a device

              pcap_free_datalinks(3)
                     free list of link-layer header types

              pcap_set_datalink(3)
                     set link-layer header type for a device

              pcap_datalink_val_to_name(3)
                     get name for a link-layer header type

              pcap_datalink_val_to_description(3)
              pcap_datalink_val_to_description_or_dlt(3)
                     get description for a link-layer header type

              pcap_datalink_name_to_val(3)
                     get link-layer header type corresponding to a name

   Reading packets
       Packets are read with pcap_dispatch() or pcap_loop(), which process one
       or more packets, calling a callback routine for each  packet,  or  with
       pcap_next() or pcap_next_ex(), which return the next packet.  The call-
       back for pcap_dispatch() and pcap_loop() is supplied  a  pointer  to  a
       struct pcap_pkthdr, which includes the following members:

              ts     a  struct timeval containing the time when the packet was
                     captured

              caplen a bpf_u_int32 giving the number of bytes  of  the  packet
                     that are available from the capture

              len    a  bpf_u_int32  giving the length of the packet, in bytes
                     (which might be more than the number of  bytes  available
                     from  the  capture, if the length of the packet is larger
                     than the maximum number of bytes to capture).

       The callback is also supplied a  const  u_char  pointer  to  the  first
       caplen  (as  given  in the struct pcap_pkthdr mentioned above) bytes of
       data from the packet.  This won't necessarily be the entire packet;  to
       capture the entire packet, you will have to provide a value for snaplen
       in your call to pcap_set_snaplen() that is sufficiently  large  to  get
       all  of  the  packet's  data - a value of 65535 should be sufficient on
       most if not all networks).  When reading from a ``savefile'', the snap-
       shot  length  specified  when  the capture was performed will limit the
       amount of packet data available.

       pcap_next() is passed an argument that points to a  struct  pcap_pkthdr
       structure,  and  fills  it in with the time stamp and length values for
       the packet.  It returns a const u_char to the first caplen bytes of the
       packet on success, and NULL on error.

       pcap_next_ex()  is passed two pointer arguments, one of which points to
       a structpcap_pkthdr* and one of which points to a  const  u_char*.   It
       sets  the first pointer to point to a struct pcap_pkthdr structure with
       the time stamp and length values for the packet, and  sets  the  second
       pointer to point to the first caplen bytes of the packet.

       To  force the loop in pcap_dispatch() or pcap_loop() to terminate, call
       pcap_breakloop().

       By default, when reading packets from an interface opened  for  a  live
       capture,  pcap_dispatch(),  pcap_next(), and pcap_next_ex() will, if no
       packets are currently available to be read, block waiting  for  packets
       to  become  available.   On  some,  but not all, platforms, if a packet
       buffer timeout was specified, the wait will terminate after the  packet
       buffer timeout expires; applications should be prepared for this, as it
       happens on some platforms, but should not rely on it, as  it  does  not
       happen  on  other  platforms.   Note that the wait might, or might not,
       terminate even if no packets are available; applications should be pre-
       pared for this to happen, but must not rely on it happening.

       A  handle can be put into ``non-blocking mode'', so that those routines
       will, rather than blocking, return an indication that  no  packets  are
       available  to  read.  Call pcap_setnonblock() to put a handle into non-
       blocking mode or to take it out of non-blocking mode; call pcap_getnon-
       block()  to  determine  whether a handle is in non-blocking mode.  Note
       that non-blocking mode does not work correctly in Mac OS X 10.6.

       Non-blocking mode is often combined with routines such as select(2)  or
       poll(2) or other routines a platform offers to wait for any of a set of
       descriptors to be ready to read.  To obtain, for a handle, a descriptor
       that  can be used in those routines, call pcap_get_selectable_fd().  If
       the routine indicates that data is available to read on the descriptor,
       an attempt should be made to read from the device.

       Not     all    handles    have    such    a    descriptor    available;
       pcap_get_selectable_fd() will return -1 if no such descriptor is avail-
       able.   If  no  such  descriptor  is available, this may be because the
       device  must  be  polled  periodically  for  packets;  in  that   case,
       pcap_get_required_select_timeout()  will  return  a pointer to a struct
       timeval whose value can be used as a timeout in those  routines.   When
       the routine returns, an attmept should be made to read packets from the
       device.  If pcap_get_required_select_timeout() returns  NULL,  no  such
       timeout  is  available,  and  those  routines  cannot  be used with the
       device.

       In addition, for various reasons, one or more of  those  routines  will
       not   work   properly   with  the  descriptor;  the  documentation  for
       pcap_get_selectable_fd() gives details.  Note that, just as an  attempt
       to  read packets from a pcap_t may not return any packets if the packet
       buffer timeout expires, a select(), poll(), or other such call may,  if
       the  packet buffer timeout expires, indicate that a descriptor is ready
       to read even if there are no packets available to read.

       Routines

              pcap_dispatch(3)
                     read a bufferful of packets from a pcap_t open for a live
                     capture or the full set of packets from a pcap_t open for
                     a ``savefile''

              pcap_loop(3)
                     read packets from a pcap_t until an  interrupt  or  error
                     occurs

              pcap_next(3)
                     read  the next packet from a pcap_t without an indication
                     whether an error occurred

              pcap_next_ex(3)
                     read the next packet from a pcap_t with an error  indica-
                     tion on an error

              pcap_breakloop(3)
                     prematurely  terminate  the  loop  in  pcap_dispatch() or
                     pcap_loop()

              pcap_setnonblock(3)
                     set or clear non-blocking mode on a pcap_t

              pcap_getnonblock(3)
                     get the state of non-blocking mode for a pcap_t

              pcap_get_selectable_fd(3)
                     attempt to get a descriptor for a pcap_t that can be used
                     in calls such as select(2) and poll(2)

              pcap_get_required_select_timeout(3)
                     attempt  to  get a timeout required for using a pcap_t in
                     calls such as select(2) and poll(2)

   Filters
       In order to cause only certain packets  to  be  returned  when  reading
       packets, a filter can be set on a handle.  For a live capture, the fil-
       tering will be performed in kernel mode, if possible, to avoid  copying
       ``uninteresting'' packets from the kernel to user mode.

       A filter can be specified as a text string; the syntax and semantics of
       the string are as described by pcap-filter(7).  A filter string is com-
       piled into a program in a pseudo-machine-language by pcap_compile() and
       the resulting program can be made a filter for a handle with  pcap_set-
       filter().   The  result  of  pcap_compile() can be freed with a call to
       pcap_freecode().  pcap_compile() may require a network mask for certain
       expressions  in the filter string; pcap_lookupnet() can be used to find
       the network address and network mask for a given capture device.

       A compiled filter can also be applied directly to  a  packet  that  has
       been read using pcap_offline_filter().

       Routines

              pcap_compile(3)
                     compile  filter  expression  to a pseudo-machine-language
                     code program

              pcap_freecode(3)
                     free a filter program

              pcap_setfilter(3)
                     set filter for a pcap_t

              pcap_lookupnet(3)
                     get network address and network mask for a capture device

              pcap_offline_filter(3)
                     apply a filter program to a packet

   Incoming and outgoing packets
       By  default,  libpcap  will attempt to capture both packets sent by the
       machine and packets received by the machine.  To limit it to  capturing
       only packets received by the machine or, if possible, only packets sent
       by the machine, call pcap_setdirection().

       Routines

              pcap_setdirection(3)
                     specify whether to  capture  incoming  packets,  outgoing
                     packets, or both

   Capture statistics
       To get statistics about packets received and dropped in a live capture,
       call pcap_stats().

       Routines

              pcap_stats(3)
                     get capture statistics

   Opening a handle for writing captured packets
       To open a ``savefile`` to which to write packets,  given  the  pathname
       the ``savefile'' should have, call pcap_dump_open().  To open a ``save-
       file`` to which to write packets, given the pathname  the  ``savefile''
       should  have,  call  pcap_dump_open(); to set up a handle for a ``save-
       file'', given a FILE * referring to a file already opened for  writing,
       call  pcap_dump_fopen().  They each return pointers to a pcap_dumper_t,
       which is the handle used for writing packets to the  ``savefile''.   If
       it  succeeds,  it  will  have  created the file if it doesn't exist and
       truncated the file if it does exist.  To close  a  pcap_dumper_t,  call
       pcap_dump_close().

       Routines

              pcap_dump_open(3)
                     open a pcap_dumper_t for a ``savefile``, given a pathname

              pcap_dump_fopen(3)
                     open a pcap_dumper_t for a ``savefile``, given a FILE *

              pcap_dump_close(3)
                     close a pcap_dumper_t

              pcap_dump_file(3)
                     get the FILE * for a pcap_dumper_t opened for  a  ``save-
                     file''

   Writing packets
       To  write a packet to a pcap_dumper_t, call pcap_dump().  Packets writ-
       ten with pcap_dump() may be buffered,  rather  than  being  immediately
       written  to the ``savefile''.  Closing the pcap_dumper_t will cause all
       buffered-but-not-yet-written packets to be written to the ``savefile''.
       To  force all packets written to the pcap_dumper_t, and not yet written
       to the ``savefile'' because they're buffered by the  pcap_dumper_t,  to
       be written to the ``savefile'', without closing the pcap_dumper_t, call
       pcap_dump_flush().

       Routines

              pcap_dump(3)
                     write packet to a pcap_dumper_t

              pcap_dump_flush(3)
                     flush buffered packets written to a pcap_dumper_t to  the
                     ``savefile''

              pcap_dump_ftell(3)
                     get current file position for a pcap_dumper_t

   Injecting packets
       If you have the required privileges, you can inject packets onto a net-
       work  with  a  pcap_t  for  a  live  capture,  using  pcap_inject()  or
       pcap_sendpacket().  (The two routines exist for compatibility with both
       OpenBSD and WinPcap/Npcap; they perform the  same  function,  but  have
       different return values.)

       Routines

              pcap_inject(3)
              pcap_sendpacket(3)
                     transmit a packet

   Reporting errors
       Some  routines return error or warning status codes; to convert them to
       a string, use pcap_statustostr().

       Routines

              pcap_statustostr(3)
                     get a string for an error or warning status code

   Getting library version information
       To  get  a  string  giving  version  information  about  libpcap,  call
       pcap_lib_version().

       Routines

              pcap_lib_version(3)
                     get library version string


BACKWARD COMPATIBILITY

       In  versions of libpcap prior to 1.0, the pcap.h header file was not in
       a pcap directory on most platforms; if you are writing  an  application
       that  must  work on versions of libpcap prior to 1.0, include <pcap.h>,
       which  will  include  <pcap/pcap.h>  for  you,  rather  than  including
       <pcap/pcap.h>.

       pcap_create()  and  pcap_activate()  were  not available in versions of
       libpcap prior to 1.0; if you are writing an application that must  work
       on versions of libpcap prior to 1.0, either use pcap_open_live() to get
       a handle for a live capture or, if you want to be able to use the addi-
       tional capabilities offered by using pcap_create() and pcap_activate(),
       use an autoconf(1) script or some other configuration script  to  check
       whether  the  libpcap  1.0 APIs are available and use them only if they
       are.


SEE ALSO

       autoconf(1),  tcpdump(1),  tcpslice(1),  pcap-filter(7),   pfconfig(8),
       usermod(8)


AUTHORS

       The original authors of libpcap are:

       Van  Jacobson,  Craig  Leres  and  Steven  McCanne, all of the Lawrence
       Berkeley National Laboratory, University of California, Berkeley, CA.

       The current version is available from "The Tcpdump Group"'s Web site at

              https://www.tcpdump.org/


BUGS

       To  report  a  security  issue  please  send an e-mail to security@tcp-
       dump.org.

       To report bugs and other problems, contribute patches, request  a  fea-
       ture,  provide generic feedback etc please see the file CONTRIBUTING.md
       in the libpcap source tree root.



                               9 September 2020                    pcap(3)

libpcap 1.10.0 - Generated Thu Dec 31 11:02:17 CST 2020
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