focal (8) ping.8.gz

Provided by: iputils-ping_20190709-3ubuntu1_amd64 bug

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 than
           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 interface name, it sets source interface
           to specified interface. NOTE: For IPv6, when doing ping to a link-local scope address, link
           specification (by the '%'-notation in destination, or by this option) can be used but it is no longer
           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.

       -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 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.

       -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 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/mdev round-trip time numbers.

       Population standard deviation (mdev), essentially an average of how far each ping RTT is from the mean
       RTT. The higher mdev is, the more variable the RTT is (over time). With a high RTT variability, you will
       have speed issues with bulk transfers (they will take longer than is strictly speaking necessary, as the
       variability will eventually cause the sender to wait for ACKs) and you will have middling to poor VoIP
       quality.

       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 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:

           • 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 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

       ip(8), ss(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.