PING linux command manual

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

       ping, ping6 - send ICMP ECHO_REQUEST to network hosts

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

       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.

       -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

       -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  hun-
              dred  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 val-
              ues less 0.2 seconds.

       -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 wait-
              ing 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  sym-
              bolic 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  prob-
              lems  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.  Traditionally (RFC1349),
              these have been interpreted as: 0 for reserved (currently being
              redefined  as  congestion 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  simultane-
              ously.   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 rede-
              fined 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]]] (times-
              tamp 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  run-
       ning.  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/average/maximum round-trip time num-
       bers.  When the specified  number  of  packets  have  been  sent  (and
       received)  or if the program is terminated with a SIGINT, a brief sum-
       mary 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.

       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

       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.

       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).

       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 partic-
       ular pattern that will have problems is something  that  doesn't  have
       sufficient  ''transitions'',  such as all ones or all zeros, or a pat-
       tern right at the edge, such as almost all zeros.  It isn't  necessar-
       ily 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.

       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 decre-
       ment 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

       ? 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

       ? 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.

       ? 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  condi-

       netstat(1), ifconfig(8).

       The ping command appeared in 4.3BSD.

       The version described here is its descendant specific to Linux.

       ping  requires CAP_NET_RAWIO capability to be executed. It may be used
       as set-uid root.

       ping is part of iputils package and the latest versions are  available
       in   source   form   for  anonymous  ftp

iputils-020927                27 September 2002                       PING(8)