Re: [RFC] netconsole.txt: "nc" needs "-p" to specify the listening port

[Rob Landley <rob@landley.net>]

On 08/02/2012 03:39 PM, Dirk Gouders wrote:
> Dirk Gouders <gouders@et.bocholt.fh-gelsenkirchen.de> writes:
> 
>> Rob Landley <rob@landley.net> writes:
>>
>>> On 07/29/2012 03:40 AM, Milton Miller wrote:
>>>> [adding Rob as Doc maintanier]
>>>>
>>>> On Sat, 28 Jul 2012 about 11:08:16 -0000, Dirk Gouders wrote:
>>>>> Borislav Petkov <bp@alien8.de> writes:
>>>>>
>>>>>> On Fri, Jul 27, 2012 at 11:24:53AM +0200, Dirk Gouders wrote:
>>>>>>> Cong Wang <xiyou.wangcong@gmail.com> writes:
>>>>>>>
>>>>>>>> On Fri, Jul 27, 2012 at 2:35 PM, Dirk Gouders
>>>>>>>> <gouders@et.bocholt.fh-gelsenkirchen.de> wrote:
>>>>>>>>> Hi Jesse,
>>>>>>>>>
>>>>>>>>> I would like to ask you to check if the documentation of "nc" in
>>>>>>>>> netconsole.txt is still correct.  I tried two different netcat packages
>>>>>>>>> and both require "-p" to specify the listening port.  I am wondering if
>>>>>>>>> that changed after the use of "nc" has been documented.
>>>>>>>>
>>>>>>>> On Fedora 16, `nc -u -l <port number>` works fine.
>>>>>>>
>>>>>>> Thanks for checking that.
>>>>>>>
>>>>>>> If the information I found is correct, Fedora uses OpenBSD's nc
>>>>>>> codebase.  The two netcat packages I tested on a Gentoo system differ in
>>>>>>> requiring the -p switch for the port specification.
>>>>>>
>>>>>> So say exactly that in the doc: that the *BSD's version of nc doesn't
>>>>>> need the port number specified with '-p' and you're covered.
>>>>> OK, I tried that in the attached patch.
>>>>> I'm not sure if every exeption needs to/should be documented, though.
>>>>>
>>>>> >From 3cdeac3e814471053129145c5fa8391acb365fd8 Mon Sep 17 00:00:00 2001
>>>>> From: Dirk Gouders <gouders@et.bocholt.fh-gelsenkirchen.de>
>>>>> Date: Sat, 28 Jul 2012 12:32:49 +0200
>>>>> Subject: [PATCH] netconsole.txt: non-BSD versions of nc(1) require '-p'
>>>>>  switch
>>>>>
>>>>> Gentoo for example uses non-BSD versions of nc(1) which require
>>>>> the '-p' switch to specify the listening port.
>>>>>
>>>>> ---
>>>>> Documentation/networking/netconsole.txt |    3 ++-
>>>>>  1 files changed, 2 insertions(+), 1 deletions(-)
>>>
>>> Did this ever resolve to a specific recommended patch? The one at the
>>> start of the thread:
>>>
>>>  http://lkml.indiana.edu/hypermail/linux/kernel/1207.3/01995.html
>>>
>>> Apparently isn't it...?
>>
>> Sorry for the delay.
>> I tested the situation on a few distributions and am still thinking
>> about a proper way to write it in a way without netconsole.txt becoming
>> a kind of "netcat.txt".
>>
>> I would be glad about comments to what I currently have -- also, because
>> I am not a native English speaker:
>>
>> ------------------------------------------------------------------------
>> The remote host can run syslogd or netcat to receive the kernel
>> messages.  On distributions using a BSD-based netcat version
>> (e.g. Fedora, openSUSE and Ubuntu) the listening port must be
>> specified without the -p switch:
>>
>> 'nc -u -l -p <port>' / 'nc -u -l <port>' or
>> 'netcat -u -l -p <port>' / 'netcat -u -l <port>'
>> ------------------------------------------------------------------------
>>
>> At the end, I also attach what I have noted during the tests with the
>> different distributions.
>>
>> Dirk
>>
>> ------------------------------------------------------------------------
>> Problem on systems where the gnu-netcat package provides a symbolic
>> link /usr/bin/nc -> /usr/bin/netcat:
>>
>> gnu-netcat requires -p to specify the local port but does not complain
>> if invoked as `nc -l -u <port>'; you need to use -v to see that it
>> does not do what you might expect:
>>
>> # nc -l -u 4444 -v
>> Warning: Inverse name lookup failed for `0.0.17.92'
>> ------------------------------------------------------------------------
>>
>> Distro		Package						needs -p
>> 		Command invocation
>> ========================================================================
>> Arch		gnu-netcat					yes
>> (Website	nc | netcat
>>  documentation)
>> 		openbsd-netcat					no
>> 		nc.openbsd
>> ------------------------------------------------------------------------
>> Debian-6.0.5	netcat-openbsd					no 
>> 		nc | netcat | nc.openbsd		   
>> 		                                   
>> 		netcat / netcat-traditional (preinstalled)	yes
>> 		nc | netcat
>> 		                                   
>> 		netcat6						yes
>> 		nc | netcat | nc6
>> ------------------------------------------------------------------------
>> Fedora-17	nc (preinstalled)				no
>> 		nc
>>
>> 		nc6
>> 		nc6						yes
>> ------------------------------------------------------------------------
>> Gentoo		gnu-netcat					yes
>> 		netcat
>>
>> 		netcat						yes
>> 		nc
>>
>> 		netcat6						yes
>> 		nc | nc6
>> ------------------------------------------------------------------------
>> OpenSUSE-12.1	netcat-openbsd					no
>> 		nc | netcat
>> ------------------------------------------------------------------------
>> Ubuntu-12.04	netcat-openbsd (preinstalled)			no 
>> Desktop		nc | netcat | nc.openbsd
>> 		                                   
>> 		netcat / netcat-traditional			yes
>> 		nc | netcat		   
>> 		                                   
>> 		netcat6						yes
>> 		nc | netcat | nc6
>> ------------------------------------------------------------------------
> 
> Here is a patch that also includes Jan's suggestion for socat(1).

Or you could use the bash built-in functionality of /dev/udp/host/port
with redirection. Or you can write a program to do it using the C API.

This seems about as silly as trying to document /proc/sys/vm/drop-caches
by listing the various ways you can write to a file.

Rob
-- 
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Either it's "mere aggregation", or a license violation.  Pick one.