PING(8) iputils PING(8)
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
hops 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 hops) 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.
.SH "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 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 functionality 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 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.
iputils 20240905 PING(8)
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