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PING(8)                          System Manager's Manual: iputils                         PING(8)



NAME
       ping - send ICMP ECHO_REQUEST to network hosts

SYNOPSIS
       ping  [-aAbBdDfhLnOqrRUvV46]  [-c  count]  [-F flowlabel] [-i interval] [-I interface] [-l
       preload] [-m mark] [-M pmtudisc_option] [-N nodeinfo_option] [-w  deadline]  [-W  timeout]
       [-p pattern] [-Q tos] [-s packetsize] [-S sndbuf] [-t ttl] [-T timestamp option] [hop ...]
       destination


DESCRIPTION
       ping  uses  the  ICMP  protocol's  mandatory  ECHO_REQUEST  datagram  to  elicit  an  ICMP
       ECHO_RESPONSE  from  a host or gateway.  ECHO_REQUEST datagrams (``pings'') have an IP and
       ICMP header, followed by a struct timeval and then an arbitrary number  of  ``pad''  bytes
       used to fill out the packet.

       ping  works  with both IPv4 and IPv6. Using only one of them explicitly can be enforced by
       specifying -4 or -6.

       ping can also send IPv6 Node Information Queries (RFC4620).  Intermediate hops may not  be
       allowed, because IPv6 source routing was deprecated (RFC5095).

OPTIONS
       -4     Use IPv4 only.

       -6     Use IPv6 only.

       -a     Audible ping.

       -A     Adaptive  ping. Interpacket interval adapts to round-trip time, so that effectively
              not more than one (or more, if preload is set) unanswered probe is present  in  the
              network.  Minimal interval is 200msec for not super-user.  On networks with low rtt
              this mode is essentially equivalent to flood mode.

       -b     Allow pinging a broadcast address.

       -B     Do not allow ping to change source address of probes.  The address is bound to  one
              selected when ping starts.

       -c count
              Stop after sending count ECHO_REQUEST packets. With deadline option, ping waits for
              count ECHO_REPLY packets, until the timeout expires.

       -d     Set the SO_DEBUG option on the socket being used.  Essentially, this socket  option
              is not used by Linux kernel.

       -D     Print timestamp (unix time + microseconds as in gettimeofday) before each line.

       -f     Flood  ping.  For every ECHO_REQUEST sent a period ``.'' is printed, while for ever
              ECHO_REPLY received a backspace is printed.  This provides a rapid display  of  how
              many packets are being dropped.  If interval is not given, it sets interval to zero
              and outputs packets as fast as they come back or  one  hundred  times  per  second,
              whichever is more.  Only the super-user may use this option with zero interval.

       -F flow label
              IPv6  only.   Allocate  and set 20 bit flow label (in hex) on echo request packets.
              If value is zero, kernel allocates random flow label.

       -h     Show help.

       -i interval
              Wait interval seconds between sending each packet.  The default is to wait for  one
              second  between each packet normally, or not to wait in flood mode. Only super-user
              may set interval to values less 0.2 seconds.

       -I interface
              interface is either an address, or an interface name.  If interface is an  address,
              it  sets  source address to specified interface address.  If interface in an inter-
              face name, it sets source interface to specified interface.  For IPv6,  when  doing
              ping to a link-local scope address, link specification (by the '%'-notation in des-
              tination, or by this option) is required.

       -l preload
              If preload is specified, ping sends that many packets not waiting for reply.   Only
              the super-user may select preload more than 3.

       -L     Suppress  loopback of multicast packets.  This flag only applies if the ping desti-
              nation is a multicast address.

       -m mark
              use mark to tag the packets going out. This is useful for variety of reasons within
              the kernel such as using policy routing to select specific outbound processing.

       -M pmtudisc_opt
              Select  Path  MTU  Discovery  strategy.  pmtudisc_option may be either do (prohibit
              fragmentation, even local one), want (do  PMTU  discovery,  fragment  locally  when
              packet size is large), or dont (do not set DF flag).

       -N nodeinfo_option
              IPv6  only.   Send  ICMPv6  Node  Information  Queries  (RFC4620),  instead of Echo
              Request.  CAP_NET_RAW capability is required.

              help   Show help for NI support.

              name   Queries for Node Names.

              ipv6   Queries for IPv6 Addresses. There are several IPv6 specific flags.

                     ipv6-global
                            Request IPv6 global-scope addresses.

                     ipv6-sitelocal
                            Request IPv6 site-local addresses.

                     ipv6-linklocal
                            Request IPv6 link-local addresses.

                     ipv6-all
                            Request IPv6 addresses on other interfaces.

              ipv4   Queries for IPv4 Addresses.  There is one IPv4 specific flag.

                     ipv4-all
                            Request IPv4 addresses on other interfaces.

              subject-ipv6=ipv6addr
                     IPv6 subject address.

              subject-ipv4=ipv4addr
                     IPv4 subject address.

              subject-name=nodename
                     Subject name.  If it contains more than one dot, fully-qualified domain name
                     is assumed.

              subject-fqdn=nodename
                     Subject name.  Fully-qualified domain name is always assumed.

       -n     Numeric  output  only.   No  attempt will be made to lookup symbolic names for host
              addresses.

       -O     Report outstanding ICMP ECHO reply before sending  next  packet.   This  is  useful
              together  with  the  timestamp -D to log output to a diagnostic file and search for
              missing answers.

       -p pattern
              You may specify up to 16 ``pad'' bytes to fill out the packet you  send.   This  is
              useful  for  diagnosing  data-dependent  problems in a network.  For example, -p ff
              will cause the sent packet to be filled with all ones.

       -q     Quiet output.  Nothing is displayed except the summary lines at  startup  time  and
              when finished.

       -Q tos Set  Quality  of Service -related bits in ICMP datagrams.  tos can be decimal (ping
              only) or hex number.

              In RFC2474, these fields are interpreted as  8-bit  Differentiated  Services  (DS),
              consisting  of:  bits 0-1 (2 lowest bits) of separate data, and bits 2-7 (highest 6
              bits) of Differentiated Services Codepoint (DSCP).  In RFC2481  and  RFC3168,  bits
              0-1 are used for ECN.

              Historically  (RFC1349,  obsoleted  by  RFC2474),  these were interpreted as: bit 0
              (lowest bit) for reserved (currently being redefined as  congestion  control),  1-4
              for Type of Service and bits 5-7 (highest bits) for Precedence.

       -r     Bypass  the normal routing tables and send directly to a host on an attached inter-
              face.  If the host is not on a directly-attached network,  an  error  is  returned.
              This option can be used to ping a local host through an interface that has no route
              through it provided the option -I is also used.

       -R     ping only.  Record route.  Includes the RECORD_ROUTE  option  in  the  ECHO_REQUEST
              packet  and displays the route buffer on returned packets.  Note that the IP header
              is only large enough for nine such routes.   Many  hosts  ignore  or  discard  this
              option.

       -s packetsize
              Specifies the number of data bytes to be sent.  The default is 56, which translates
              into 64 ICMP data bytes when combined with the 8 bytes of ICMP header data.

       -S sndbuf
              Set socket sndbuf. If not specified, it is selected to buffer  not  more  than  one
              packet.

       -t ttl ping only.  Set the IP Time to Live.

       -T timestamp option
              Set  special  IP  timestamp  options.   timestamp option may be either tsonly (only
              timestamps), tsandaddr (timestamps and addresses) or tsprespec host1 [host2  [host3
              [host4]]] (timestamp prespecified hops).

       -U     Print  full  user-to-user latency (the old behaviour). Normally ping prints network
              round trip time, which can be different f.e. due to DNS failures.

       -v     Verbose output.

       -V     Show version and exit.

       -w deadline
              Specify a timeout, in seconds, before ping exits regardless  of  how  many  packets
              have  been sent or received. In this case ping does not stop after count packet are
              sent, it waits either for deadline expire or until count probes are answered or for
              some error notification from network.

       -W timeout
              Time to wait for a response, in seconds. The option affects only timeout in absence
              of any responses, otherwise ping waits for two RTTs.

       When using ping for fault isolation, it should first be run on the local host,  to  verify
       that  the  local network interface is up and running. Then, hosts and gateways further and
       further away should be ``pinged''. Round-trip times and packet loss  statistics  are  com-
       puted.  If duplicate packets are received, they are not included in the packet loss calcu-
       lation, although the round trip time of these packets is used  in  calculating  the  mini-
       mum/average/maximum  round-trip  time  numbers.  When the specified number of packets have
       been sent (and received) or if the program is terminated with a SIGINT, a brief summary is
       displayed.  Shorter current statistics can be obtained without termination of process with
       signal SIGQUIT.

       If ping does not receive any reply packets at all it will exit with code 1.  If  a  packet
       count  and  deadline  are both specified, and fewer than count packets are received by the
       time the deadline has arrived, it will also exit with code 1.  On  other  error  it  exits
       with  code  2. Otherwise it exits with code 0. This makes it possible to use the exit code
       to see if a host is alive or not.

       This program is intended for use in network testing, measurement and management.   Because
       of  the  load  it can impose on the network, it is unwise to use ping during normal opera-
       tions or from automated scripts.

ICMP PACKET DETAILS
       An IP header without options is 20 bytes.  An ICMP ECHO_REQUEST packet contains  an  addi-
       tional 8 bytes worth of ICMP header followed by an arbitrary amount of data.  When a pack-
       etsize is given, this indicated the size of this extra piece of data (the default is  56).
       Thus  the  amount  of  data  received  inside of an IP packet of type ICMP ECHO_REPLY will
       always be 8 bytes more than the requested data space (the ICMP header).

       If the data space is at least of size of struct timeval ping uses the beginning  bytes  of
       this  space  to  include a timestamp which it uses in the computation of round trip times.
       If the data space is shorter, no round trip times are given.

DUPLICATE AND DAMAGED PACKETS
       ping will report duplicate and damaged packets.  Duplicate packets should never occur, and
       seem  to  be  caused by inappropriate link-level retransmissions.  Duplicates may occur in
       many situations and are rarely (if ever) a good sign, although the presence of low  levels
       of duplicates may not always be cause for alarm.

       Damaged  packets  are obviously serious cause for alarm and often indicate broken hardware
       somewhere in the ping packet's path (in the network or in the hosts).

TRYING DIFFERENT DATA PATTERNS
       The (inter)network layer should never treat packets differently depending on the data con-
       tained  in  the  data  portion.  Unfortunately, data-dependent problems have been known to
       sneak into networks and remain undetected for long periods of time.   In  many  cases  the
       particular  pattern  that  will  have  problems  is something that doesn't have sufficient
       ``transitions'', such as all ones or all zeros, or a pattern right at the  edge,  such  as
       almost all zeros.  It isn't necessarily enough to specify a data pattern of all zeros (for
       example) on the command line because the pattern that is of interest is at the  data  link
       level, and the relationship between what you type and what the controllers transmit can be
       complicated.

       This means that if you have a data-dependent problem you will probably have to do a lot of
       testing  to find it.  If you are lucky, you may manage to find a file that either can't be
       sent across your network or that takes much longer to transfer than other  similar  length
       files.   You  can then examine this file for repeated patterns that you can test using the
       -p option of ping.

TTL DETAILS
       The TTL value of an IP packet represents the maximum number of IP routers that the  packet
       can  go  through before being thrown away.  In current practice you can expect each router
       in the Internet to decrement the TTL field by exactly one.

       The TCP/IP specification states that the TTL field for TCP packets should be  set  to  60,
       but many systems use smaller values (4.3 BSD uses 30, 4.2 used 15).

       The  maximum  possible value of this field is 255, and most Unix systems set the TTL field
       of ICMP ECHO_REQUEST packets to 255.  This is why you will  find  you  can  ``ping''  some
       hosts, but not reach them with telnet(1) or ftp(1).

       In  normal operation ping prints the TTL value from the packet it receives.  When a remote
       system receives a ping packet, it can do one of three things with the  TTL  field  in  its
       response:

       o Not  change  it; this is what Berkeley Unix systems did before the 4.3BSD Tahoe release.
         In this case the TTL value in the received packet  will  be  255  minus  the  number  of
         routers in the round-trip path.

       o Set  it  to  255;  this  is what current Berkeley Unix systems do.  In this case the TTL
         value in the received packet will be 255 minus the number of routers in  the  path  from
         the remote system to the pinging host.

       o Set  it to some other value. Some machines use the same value for ICMP packets that they
         use for TCP packets, for example either 30 or 60.  Others may use completely  wild  val-
         ues.

BUGS
       o Many Hosts and Gateways ignore the RECORD_ROUTE option.

       o The maximum IP header length is too small for options like RECORD_ROUTE to be completely
         useful.  There's not much that can be done about this, however.

       o Flood pinging is not recommended in general, and flood  pinging  the  broadcast  address
         should only be done under very controlled conditions.

SEE ALSO
       netstat(1), ifconfig(8).

HISTORY
       The ping command appeared in 4.3BSD.

       The version described here is its descendant specific to Linux.

       As  of version s20150815, the ping6 binary doesn't exist anymore.  It has been merged into
       ping. Creating a symlink named ping6 pointing to ping will result in the same funcionality
       as before.

SECURITY
       ping requires CAP_NET_RAW capability to be executed 1) if the program is used for non-echo
       queries (See -N option), or 2) if kernel does not support non-raw ICMP sockets, or  3)  if
       the user is not allowed to create an ICMP echo socket.  The program may be used as set-uid
       root.

AVAILABILITY
       ping is part of iputils package and the latest versions are  available in source  form  at
       http://www.skbuff.net/iputils/iputils-current.tar.bz2.



iputils-160308                                                                            PING(8)

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