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 flowlabel] [ -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.
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 label.
-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.
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 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
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 desti-
nation is a multicast address.
-n Numeric output only. No attempt will be made to lookup symbolic names for host
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 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 simultaneously. Possible settings for special Precedence range
from priority (0x20) to net control (0xe0). You must be root (CAP_NET_ADMIN capa-
bility) 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 redefined 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
-q Quiet output. Nothing is displayed except the summary lines at startup time and
-R Record route. Includes the RECORD_ROUTE option in the ECHO_REQUEST packet and dis-
plays 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 inter-
face. 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.
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.
Set socket sndbuf. If not specified, it is selected to buffer not more than one
-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]]] (timestamp prespecified hops).
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.
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.
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 running. Then, hosts and gateways further and
further away should be ``pinged''. Round-trip times and packet loss statistics are com-
puted. If duplicate packets are received, they are not included in the packet loss calcu-
lation, although the round trip time of these packets is used in calculating the mini-
mum/average/maximum round-trip time numbers. 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
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 opera-
tions or from automated scripts.
ICMP PACKET DETAILS
An IP header without options is 20 bytes. An ICMP ECHO_REQUEST packet contains an addi-
tional 8 bytes worth of ICMP header followed by an arbitrary amount of data. When a pack-
etsize 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 con-
tained 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
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 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
o 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.
o 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.
o 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 val-
o Many Hosts and Gateways ignore the RECORD_ROUTE option.
o 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.
o Flood pinging is not recommended in general, and flood pinging the broadcast address
should only be done under very controlled conditions.
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 ftp://ftp.inr.ac.ru/ip-routing/iputils-current.tar.gz.
iputils-020927 27 September 2002 PING(8)