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



NAME
       ping, ping6 - send ICMP ECHO_REQUEST to network hosts

SYNOPSIS
       ping [ -LRUbdfnqrvVaAB]  [ -c count]  [ -i interval]  [ -l preload]  [ -p pattern]  [ -s packetsize]  [ -t ttl]
       [ -w deadline]  [ -F flowlabel]  [ -I interface]  [ -M hint]  [ -Q tos]  [ -S sndbuf]  [ -T  timestamp  option]
       [ -W timeout]  [ 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.

OPTIONS
       -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 probes 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.

       -F flow label
              Allocate and set 20 bit flow label on echo request packets.  (Only ping6).  If  value  is  zero,  kernel
              allocates random flow label.

       -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.

       -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 sec-
              onds.

       -I interface address
              Set source address to specified interface address. Argument may be numeric IP address or name of device.
              When pinging IPv6 link-local address 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 destination is  a  multicast
              address.

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

       -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 tos Set  Quality of Service -related bits in ICMP datagrams.  tos can be either decimal or hex number.  Tra-
              ditionally (RFC1349), these have been interpreted as: 0 for reserved (currently being redefined as  con-
              gestion control), 1-4 for Type of Service and 5-7 for Precedence.  Possible settings for Type of Service
              are: minimal cost: 0x02, reliability: 0x04, throughput: 0x08, low delay: 0x10.  Multiple TOS bits should
              not  be  set simultaneously.  Possible settings for special Precedence range from priority (0x20) to net
              control (0xe0).  You must be root (CAP_NET_ADMIN capability) to use Critical or higher precedence value.
              You  cannot set bit 0x01 (reserved) unless ECN has been enabled in the kernel.  In RFC2474, these fields
              has been redefined as 8-bit Differentiated Services (DS), consisting of: bits 0-1 of separate data  (ECN
              will be used, here), and bits 2-7 of Differentiated Services Codepoint (DSCP).

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

       -R     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.

       -r     Bypass  the  normal routing tables and send directly to a host on an attached interface.  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.

       -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 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).

       -M hint
              Select  Path  MTU  Discovery  strategy.  hint 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).

       -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 absense 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 computed.  If duplicate packets are received, they are not included in the
       packet loss calculation, although the round trip time of these packets is used in calculating the minimum/aver-
       age/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 operations or from automated scripts.

ICMP PACKET DETAILS
       An IP header without options is 20 bytes.  An ICMP ECHO_REQUEST packet contains an additional 8 bytes worth  of
       ICMP  header  followed  by an arbitrary amount of data.  When a packetsize 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  contained  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 com-
       mand  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:

       ? 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.

       ? 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.

       ? 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 values.

BUGS
       ? Many Hosts and Gateways ignore the RECORD_ROUTE option.

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

       ? 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.

SECURITY
       ping requires CAP_NET_RAWIO capability to be executed. It 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-071127                   22 March 2017                         PING(8)