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doc/ping.sgml
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YOSHIFUJI Hideaki
ping,ping6 doc: More description on CAP_NET_RAW usage.
15 апр 2015, 14:57
15 апр 2015, 14:57864b0ff
<refentry id="ping">

<refmeta>
<refentrytitle>ping</refentrytitle>
<manvolnum>8</manvolnum>
<refmiscinfo>iputils-&snapshot;</refmiscinfo>
</refmeta>

<refnamediv>
<refname>ping, ping6</refname>
<refpurpose>send ICMP ECHO_REQUEST to network hosts</refpurpose>
</refnamediv>

<refsynopsisdiv>
<cmdsynopsis>
<command>ping</command>
<arg choice="opt"><option>-aAbBdDfhLnOqrRUvV</option></arg>
<arg choice="opt">-c <replaceable/count/</arg>
<arg choice="opt">-F <replaceable/flowlabel/</arg>
<arg choice="opt">-i <replaceable/interval/</arg>
<arg choice="opt">-I <replaceable/interface/</arg>
<arg choice="opt">-l <replaceable/preload/</arg>
<arg choice="opt">-m <replaceable/mark/</arg>
<arg choice="opt">-M <replaceable/pmtudisc_option/</arg>
<arg choice="opt">-N <replaceable/nodeinfo_option/</arg>
<arg choice="opt">-w <replaceable/deadline/</arg>
<arg choice="opt">-W <replaceable/timeout/</arg>
<arg choice="opt">-p <replaceable/pattern/</arg>
<arg choice="opt">-Q <replaceable/tos/</arg>
<arg choice="opt">-s <replaceable/packetsize/</arg>
<arg choice="opt">-S <replaceable/sndbuf/</arg>
<arg choice="opt">-t <replaceable/ttl/</arg>
<arg choice="opt">-T <replaceable/timestamp option/</arg>
<arg choice="opt" rep="repeat"><replaceable/hop/</arg>
<arg choice="req"><replaceable/destination/</arg>
</cmdsynopsis>
</refsynopsisdiv>

<refsect1><title>DESCRIPTION</title>
<para>
<command/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 <structname/struct timeval/ and then an arbitrary
number of ``pad'' bytes used to fill out the packet.
</para>
<para>
<command/ping6/ is IPv6 version of <command/ping/, and can also send Node Information Queries (RFC4620).
Intermediate <replaceable/hop/s may not be allowed, because IPv6 source routing was deprecated (RFC5095).
</para>
</refsect1>

<refsect1><title>OPTIONS</title>

<variablelist>
 <varlistentry>
  <term><option/-a/</term>
  <listitem><para>
Audible ping.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-A/</term>
  <listitem><para>
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.  
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-b/</term>
  <listitem><para>
Allow pinging a broadcast address.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-B/</term>
  <listitem><para>
Do not allow <command/ping/ to change source address of probes.
The address is bound to one selected when <command/ping/ starts.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option><anchor id="ping.count">-c <replaceable/count/</option></term>
  <listitem><para>
Stop after sending <replaceable/count/ ECHO_REQUEST
packets. With 
<link linkend="ping.deadline"><replaceable/deadline/</link>
option, <command/ping/ waits for
<replaceable/count/ ECHO_REPLY packets, until the timeout expires.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-d/</term>
  <listitem><para>
Set the <constant/SO_DEBUG/ option on the socket being used.
Essentially, this socket option is not used by Linux kernel. 
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-D/</term>
  <listitem><para>
Print timestamp (unix time + microseconds as in gettimeofday) before
each line.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-f/</term>
  <listitem><para>
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.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-F <replaceable/flow label/</option></term>
  <listitem><para>
<command/ping6/ only.
Allocate and set 20 bit flow label (in hex) on echo request packets.
If value is zero, kernel allocates random flow label.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-h/</term>
  <listitem><para>
Show help.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-i <replaceable/interval/</option></term>
  <listitem><para>
Wait <replaceable/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.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-I <replaceable/interface/</option></term>
  <listitem><para>
<replaceable/interface/ is either an address, or an interface name.
If <replaceable/interface/ is an address, it sets source address
to specified interface address.
If <replaceable/interface/ in an interface name, it sets
source interface to specified interface.
For <command/ping6/, when doing ping to a link-local scope
address, link specification (by the '%'-notation in
<replaceable/destination/, or by this option) is required.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-l <replaceable/preload/</option></term>
  <listitem><para>
If <replaceable/preload/ is specified,
<command/ping/ sends that many packets not waiting for reply.
Only the super-user may select preload more than 3.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-L/</term>
  <listitem><para>
Suppress loopback of multicast packets.  This flag only applies if the ping
destination is a multicast address.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-m <replaceable/mark/</option></term>
  <listitem><para>
use <replaceable/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.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-M <replaceable/pmtudisc_opt/</option></term>
  <listitem><para>
Select Path MTU Discovery strategy.
<replaceable/pmtudisc_option/ may be either <replaceable/do/
(prohibit fragmentation, even local one), 
<replaceable/want/ (do PMTU discovery, fragment locally when packet size
is large), or <replaceable/dont/ (do not set DF flag).
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-N <replaceable/nodeinfo_option/</option></term>
  <listitem><para>
<command/ping6/ only.
Send ICMPv6 Node Information Queries (RFC4620), instead of Echo Request.
<constant/CAP_NET_RAW/ capability is required.
   <variablelist>
    <varlistentry>
     <term><option>help</option></term>
     <listitem><para>Show help for NI support.</para></listitem>
    </varlistentry>
   </variablelist>
   <variablelist>
    <varlistentry>
     <term><option>name</option></term>
     <listitem><para>Queries for Node Names.</para></listitem>
    </varlistentry>
   </variablelist>
   <variablelist>
    <varlistentry>
     <term><option>ipv6</option></term>
     <listitem><para>Queries for IPv6 Addresses. There are several IPv6 specific flags.
      <variablelist>
       <varlistentry>
        <term><option>ipv6-global</option></term>
        <listitem><para>Request IPv6 global-scope addresses.</para></listitem> 
       </varlistentry>
      </variablelist>
      <variablelist>
       <varlistentry>
        <term><option>ipv6-sitelocal</option></term>
        <listitem><para>Request IPv6 site-local addresses.</para></listitem> 
       </varlistentry>
      </variablelist>
      <variablelist>
       <varlistentry>
        <term><option>ipv6-linklocal</option></term>
        <listitem><para>Request IPv6 link-local addresses.</para></listitem> 
       </varlistentry>
      </variablelist>
      <variablelist>
       <varlistentry>
        <term><option>ipv6-all</option></term>
        <listitem><para>Request IPv6 addresses on other interfaces.</para></listitem> 
       </varlistentry>
      </variablelist>
     </para></listitem>
    </varlistentry>
   </variablelist>
   <variablelist>
    <varlistentry>
     <term><option>ipv4</option></term>
     <listitem><para>Queries for IPv4 Addresses.  There is one IPv4 specific flag.
      <variablelist>
       <varlistentry>
        <term><option>ipv4-all</option></term>
        <listitem><para>Request IPv4 addresses on other interfaces.</para></listitem>
       </varlistentry>
      </variablelist>
     </para></listitem>
    </varlistentry>
   </variablelist>
   <variablelist>
    <varlistentry>
     <term><option>subject-ipv6=<replaceable/ipv6addr/</option></term>
     <listitem><para>IPv6 subject address.</para></listitem>
    </varlistentry>
   </variablelist>
   <variablelist>
    <varlistentry>
     <term><option>subject-ipv4=<replaceable/ipv4addr/</option></term>
     <listitem><para>IPv4 subject address.</para></listitem>
    </varlistentry>
   </variablelist>
   <variablelist>
    <varlistentry>
     <term><option>subject-name=<replaceable/nodename/</option></term>
     <listitem><para>Subject name.  If it contains more than one dot,
	fully-qualified domain name is assumed.</para></listitem>
    </varlistentry>
   </variablelist>
   <variablelist>
    <varlistentry>
     <term><option>subject-fqdn=<replaceable/nodename/</option></term>
     <listitem><para>Subject name.  Fully-qualified domain name is
	always assumed.</para></listitem>
    </varlistentry>
   </variablelist>
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-n/</term>
  <listitem><para>
Numeric output only.
No attempt will be made to lookup symbolic names for host addresses.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-O/</term>
  <listitem><para>
Report outstanding ICMP ECHO reply before sending next packet.
This is useful together with the timestamp <option>-D</option> to
log output to a diagnostic file and search for missing answers.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-p <replaceable/pattern/</option></term>
  <listitem><para>
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, <option>-p ff</option> will cause the sent packet
to be filled with all ones.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-q/</term>
  <listitem><para>
Quiet output.
Nothing is displayed except the summary lines at startup time and
when finished.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-Q <replaceable/tos/</option></term>
  <listitem><para>
	Set Quality of Service -related bits in ICMP datagrams.
	<replaceable/tos/ can be decimal (<command/ping/ only) or hex number.
	</para>
	<para>
	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.
	</para>
	<para>
	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.
   </para>
  </listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-r/</term>
  <listitem><para>
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 <option/-I/ is also
used.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-R/</term>
  <listitem><para>
<command/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.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-s <replaceable/packetsize/</option></term>
  <listitem><para>
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.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-S <replaceable/sndbuf/</option></term>
  <listitem><para>
Set socket sndbuf. If not specified, it is selected to buffer
not more than one packet.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-t <replaceable/ttl/</option></term>
  <listitem><para>
<command/ping/ only.
Set the IP Time to Live.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-T <replaceable/timestamp option/</option></term>
  <listitem><para>
Set special IP timestamp options.
<replaceable/timestamp option/ may be either 
<replaceable/tsonly/ (only timestamps), 
<replaceable/tsandaddr/ (timestamps and addresses) or 
<replaceable/tsprespec host1 [host2 [host3 [host4]]]/
(timestamp prespecified hops).
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-U/</term>
  <listitem><para>
Print full user-to-user latency (the old behaviour). Normally
<command/ping/
prints network round trip time, which can be different
f.e. due to DNS failures. 
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-v/</term>
  <listitem><para>
Verbose output.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option/-V/</term>
  <listitem><para>
Show version and exit.
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option><anchor id="ping.deadline">-w <replaceable/deadline/</option></term>
  <listitem><para>
Specify a timeout, in seconds, before
<command/ping/
exits regardless of how many
packets have been sent or received. In this case
<command/ping/
does not stop after
<link linkend="ping.count"><replaceable/count/</link>
packet are sent, it waits either for
<link linkend="ping.deadline"><replaceable/deadline/</link>
expire or until
<link linkend="ping.count"><replaceable/count/</link>
probes are answered or for some error notification from network.   
  </para></listitem>
 </varlistentry>
 <varlistentry>
  <term><option>-W <replaceable/timeout/</option></term>
  <listitem><para>
Time to wait for a response, in seconds. The option affects only timeout
in absence of any responses, otherwise <command/ping/ waits for two RTTs.
  </para></listitem>
 </varlistentry>
</variablelist>

<para>
When using <command/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 round-trip time numbers.
When the specified number of packets have been sent (and received) or
if the program is terminated with a
<constant/SIGINT/, a brief summary is displayed. Shorter current statistics
can be obtained without termination of process with signal
<constant/SIGQUIT/.
</para>

<para>
If <command/ping/ does not receive any reply packets at all it will
exit with code 1. If a packet 
<link linkend="ping.count"><replaceable/count/</link>
and
<link linkend="ping.deadline"><replaceable/deadline/</link>
are both specified, and fewer than
<link linkend="ping.count"><replaceable/count/</link>
packets are received by the time the
<link linkend="ping.deadline"><replaceable/deadline/</link>
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.
</para>


<para>
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
<command/ping/ during normal operations or from automated scripts.
</para>

</refsect1>


<refsect1><title>ICMP PACKET DETAILS</title>

<para>
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 <replaceable/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).
</para>

<para>
If the data space is at least of size of <structname/struct timeval/
<command/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.
</para>

</refsect1>

<refsect1><title>DUPLICATE AND DAMAGED PACKETS</title>

<para>
<command/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.
</para>

<para>
Damaged packets are obviously serious cause for alarm and often
indicate broken hardware somewhere in the
<command/ping/ packet's path (in the network or in the hosts).
</para>

</refsect1>

<refsect1><title>TRYING DIFFERENT DATA PATTERNS</title>

<para>
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.
</para>

<para>
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 <option/-p/ option of <command/ping/.
</para>

</refsect1>

<refsect1><title>TTL DETAILS</title>

<para>
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.
</para>

<para>
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).
</para>

<para>
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
<citerefentry><refentrytitle/telnet/<manvolnum/1/</citerefentry>
or
<citerefentry><refentrytitle/ftp/<manvolnum/1/</citerefentry>.
</para>

<para>
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:
</para>

<itemizedlist>
 <listitem><para>
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.
 </para></listitem>
 <listitem><para>
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 <emphasis/from/
the remote system <emphasis/to/ the <command/ping/ing host.
 </para></listitem>
 <listitem><para>
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.
 </para></listitem>
</itemizedlist>

</refsect1>

<refsect1><title>BUGS</title>

<itemizedlist>
 <listitem><para>
Many Hosts and Gateways ignore the RECORD_ROUTE option.
 </para></listitem>
 <listitem><para>
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.
 </para></listitem>
 <listitem><para>
Flood pinging is not recommended in general, and flood pinging the
broadcast address should only be done under very controlled conditions.
 </para></listitem>
</itemizedlist>

</refsect1>

<refsect1><title>SEE ALSO</title>
<para>
<citerefentry><refentrytitle/netstat/<manvolnum/1/</citerefentry>,
<citerefentry><refentrytitle/ifconfig/<manvolnum/8/</citerefentry>.
</para>
</refsect1>

<refsect1><title>HISTORY</title>
<para>
The <command/ping/ command appeared in 4.3BSD.
</para>
<para>
The version described here is its descendant specific to Linux.
</para>
</refsect1>

<refsect1><title>SECURITY</title>
<para>
<command/ping/ requires <constant/CAP_NET_RAW/ capability
to be executed 1) if the program is used for non-echo queries
(See <option>-N</option> 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.
</para>
</refsect1>

<refsect1><title>AVAILABILITY</title>
<para>
<command/ping/ is part of <filename/iputils/ package
and the latest versions are  available in source form at
<ulink url="http://www.skbuff.net/iputils/iputils-current.tar.bz2">
http://www.skbuff.net/iputils/iputils-current.tar.bz2</ulink>.
</para>
</refsect1>

<![IGNORE[
<refsect1><title>COPYING</title>
<para>
<literallayout>
Copyright (c) 1989 The Regents of the University of California.
All rights reserved.

This code is derived from software contributed to Berkeley by
Mike Muuss.

Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
   notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
   notice, this list of conditions and the following disclaimer in the
   documentation and/or other materials provided with the distribution.
3. All advertising materials mentioning features or use of this software
   must display the following acknowledgement:
	This product includes software developed by the University of
	California, Berkeley and its contributors.
4. Neither the name of the University nor the names of its contributors
   may be used to endorse or promote products derived from this software
   without specific prior written permission.

THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
SUCH DAMAGE.
</literallayout>
</para>
</refsect1>
]]>


</refentry>