[mythtv-commits] Ticket #3856: SQL error with rev 14225
MythTV
mythtv at cvs.mythtv.org
Tue Aug 21 07:40:53 UTC 2007
#3856: SQL error with rev 14225
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Reporter: Benoit LORAND <benoit.lorand at blorand.org> | Owner: nigel
Type: defect | Status: assigned
Priority: blocker | Milestone: unknown
Component: mythtv | Version: unknown
Severity: high | Resolution:
Mlocked: 0 |
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Comment(by Benoît LORAND <benoit.lorand at blorand.org>):
Thanks, indeed my ping command doesn't support -t parameter as you can see
down. I'm using an linux system based on lfs-6.2
(www.linuxfromscratch.org).
-------------------------------------------------------------------------------
root at MythTV:~# ping --help
Usage: ping [OPTION]... [ADDRESS]...
Informational options:
-h, --help display this help and exit
-L, --license display license and exit
-V, --version output version information and exit
Options controlling ICMP request types:
--echo Send ICMP_ECHO requests (default)
--address Send ICMP_ADDRESS packets
--timestamp Send ICMP_TIMESTAMP packets
--router Send ICMP_ROUTERDISCOVERY packets
Options valid for all request types:
-c, --count N stop after sending N packets
-d, --debug set the SO_DEBUG option
-i, --interval N wait N seconds between sending each packet
-n, --numeric do not resolve host addresses
-r, --ignore-routing send directly to a host on an attached network
-v, --verbose verbose output
Options valid for --echo requests:
* -f, --flood flood ping
* -l, --preload N send N packets as fast as possible before falling
into
normal mode of behavior
-p, --pattern PAT fill ICMP packet with given pattern (hex)
-q, --quiet quiet output
-R, --route record route
-s, --size N set number of data octets to send
Options marked with an * are available only to super-user
report bugs to bug-inetutils at gnu.org.
--------------------------------------------------------------------------------
PING(8) BSD System
Manager's Manual
PING(8)
NAME
ping - send ICMP ECHO_REQUEST packets to network hosts
SYNOPSIS
ping [-Rdfnqrv] [-c count] [-i wait] [-l preload] [-p pattern] [-s
packetsize] host
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.
The options are as follows:
-c count
Stop after sending (and receiving) count ECHO_RESPONSE
packets.
-d Set the SO_DEBUG option on the socket being used.
-f Flood ping. Outputs packets as fast as they come back or one
hundred times per second, whichever is more. 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. Only the super-user may use this option.
This can be very hard on a network and should be used with caution.
-i wait
Wait wait seconds between sending each packet. The default
is to wait for one second between each packet. This option is
incompatible with
the -f option.
-l preload
If preload is specified, ping sends that many packets as fast
as possible before falling into its normal mode of behavior.
-n Numeric output only. No attempt will be made to lookup
symbolic names for host addresses.
-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.
-R 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.
-r Bypass the normal routing tables and send directly to a host
on an attached network. 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 (e.g., after the
inter-
face was dropped by routed(8)).
-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.
-v Verbose output. ICMP packets other than ECHO_RESPONSE that
are received are listed.
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
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.
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.
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 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 eight bytes large, ping uses the first
eight bytes of this space to include a timestamp which it uses in the
computa-
tion of round trip times. If less than eight bytes of pad are
specified, 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
retransmis-
sions. 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 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 exam-
ine 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 prac-
tice 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 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.
Oth-
ers 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 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
netstat(1), ifconfig(8), routed(8)
HISTORY
The ping command appeared in 4.3BSD.
4.3 Berkeley Distribution
April 28, 1995 4.3 Berkeley
Distribution
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--
Ticket URL: <http://svn.mythtv.org/trac/ticket/3856#comment:5>
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