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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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PING(8) iputils PING(8)
ping - send ICMP ECHO_REQUEST to network hosts
ping [-aAbBdCDfhHLnOqrRUvV46] [-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}
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).
-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. Override previously defined -n option.
-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.
-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. 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.
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.
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.
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.
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).
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.
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.
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 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.
• 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.
ip(8), ss(8).
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 functionality as before.
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.
ping is part of iputils package.
This page is part of the iputils (IP utilities) project.
Information about the project can be found at
⟨http://www.skbuff.net/iputils/⟩. If you have a bug report for
this manual page, send it to [email protected],
[email protected]. This page was obtained from the
project's upstream Git repository
⟨https://github.com/iputils/iputils.git⟩ on 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-10.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
[email protected]
iputils 20240117 PING(8)
Pages that refer to this page: arping(8), clockdiff(8), tracepath(8), traceroute(8)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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