# ping

## NAME



           ping - send ICMP ECHO_REQUEST to network hosts
    


## SYNOPSIS



    
           **ping**[**-aAbBdCDfhHLnOqrRUvV346**] [**-c** _count_] [**-e** _identifier_]
                [**-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 _hop_ s may not be allowed, because IPv6 source routing
           was deprecated (RFC5095).
    


## OPTIONS



           **-3**
               RTT precision (do not round up the result time).
    
           **-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. The default
               interval is 2 ms, for more info see option **-i**. 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.
    
           **-C**
               Call connect() syscall on socket creation.
    
           **-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.
    
           **-e** _identifier_
               Set the identification field of ECHO_REQUEST. Value 0 implies
               using _raw socket_ (not supported on _ICMP datagram socket_). The
               value of the field may be printed with **-v** option.
    
           **-f**
               Flood ping. For every ECHO_REQUEST sent a period “.” is
               printed, while for every 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.
    
           **-H**
               Force DNS name resolution for the output. Useful for numeric
               destination, or **-f** option, which by default do not perform it.
               It can also help to workaround DNS resolution problems.
               Override previously defined **-n** option. See also
               _IPUTILS_PING_PTR_LOOKUP_ environment variable.
    
           **-i** _interval_
               Wait _interval_ seconds between sending each packet. Real number
               allowed with dot as a decimal separator (regardless locale
               setup). 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 2 ms. Broadcast and
               multicast ping have even higher limitation for regular user:
               minimum is 1 sec.
    
           **-I** _interface_
               _interface_ is either an address, an interface name or a VRF
               name. If _interface_ is an address, it sets source address to
               specified interface address. If _interface_ is an interface
               name, it sets source interface to specified interface. If
               _interface_ is a VRF name, each packet is routed using the
               corresponding routing table; in this case, the **-I** option can
               be repeated to specify a source address. 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. CAP_NET_ADMIN
               or CAP_NET_RAW (since Linux 5.17) capability is required, see
               socket(7).
    
           **-M** _pmtudisc_opt_
               Select Path MTU Discovery strategy.  _pmtudisc_option_ may be
               either _do_ (set DF flag but subject to PMTU checks by kernel,
               packets too large will be rejected), _want_ (do PMTU discovery,
               fragment locally when packet size is large), _probe_ (set DF
               flag and bypass PMTU checks, useful for probing), or _dont_ (do
               not set DF flag).
    
           **-N** _nodeinfo_option_
               IPv6 only. Send IPv6 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 (no reverse DNS resolution).
               This is the default for numeric destination or **-f** option.
               Override previously defined **-H** option. See also
               _IPUTILS_PING_PTR_LOOKUP_ environment variable.
    
           **-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. The maximum allowed
               value is 65507 for IPv4 (65467 when **-R** or **-T** or Intermediate
               _hop_ s) or 65527 for IPv6, but most systems limit this to a
               smaller, system-dependent number.
    
           **-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. Do not suppress DUP replies when pinging
               multicast address.
    
           **-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. Real number allowed with dot as a decimal
               separator (regardless locale setup). 0 means infinite timeout.
    
           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.
    
           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.
    


## ENVIRONMENT



           _IPUTILS_PING_PTR_LOOKUP_ environment variable set to 0 disable
           reverse DNS resolution (PTR lookup) by default. It will be
           overrided by **-H** or **-n** option.
    


## EXIT STATUS



           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.
    


## IPV6 LINK-LOCAL DESTINATIONS



           For IPv6, when the destination address has link-local scope and
           **ping** is using _ICMP datagram sockets_ , the output interface must be
           specified. When **ping** is using _raw sockets_ , it is not strictly
           necessary to specify the output interface but it should be done to
           avoid ambiguity when there are multiple possible output
           interfaces.
    
           There are two ways to specify the output interface:
    
           • using the _% notation_
               The destination address is postfixed with _%_ and the output
               interface name or ifindex, for example:
    
               **ping fe80::5054:ff:fe70:67bc%eth0**
    
               **ping fe80::5054:ff:fe70:67bc%2**
    
           • using the _-I option_
               When using _ICMP datagram sockets_ , this method is supported
               since the following kernel versions: 5.17, 5.15.19, 5.10.96,
               5.4.176, 4.19.228, 4.14.265. Also it is not supported on musl
               libc.
    


## 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 indicates 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).
    


## ID COLLISIONS



           Unlike TCP and UDP, which use port to uniquely identify the
           recipient to deliver data, ICMP uses identifier field (ID) for
           identification. Therefore, if on the same machine, at the same
           time, two ping processes use the same ID, echo reply can be
           delivered to a wrong recipient. This is a known problem due to the
           limited size of the 16-bit ID field. That is a historical
           limitation of the protocol that cannot be fixed at the moment
           unless we encode an ID into the ping packet payload.  **ping** prints
           _DIFFERENT ADDRESS_ error and packet loss is negative.
    
           **ping** uses PID to get unique number. The default value of
           _/proc/sys/kernel/pid_max_ is 32768. On the systems that use ping
           heavily and with _pid_max_ greater than 65535 collisions are bound
           to happen.
    


## 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 TTL field for TCP packets may take various values. The maximum
           possible value of this field is 255, a recommended initial value
           is 64. For more information, see the TCP/Lower-Level Interface
           section of RFC9293.
    
           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 **ping** ing 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.
    


## SECURITY



           **ping** requires CAP_NET_RAW capability to be executed 1) if the
           program is used for non-echo queries (see **-N** option) or when the
           identification field set to 0 for ECHO_REQUEST (see **-e**), or 2) if
           kernel does not support ICMP datagram 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.
    


* * *