Re: Unit of /proc/sys/kernel/random/poolsize

["Michael Kerrisk (man-pages)" <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>]

Hello Walter,

On 12/17/2015 09:56 PM, walter harms wrote:
> 
> 
> Am 17.12.2015 08:51, schrieb Michael Kerrisk (man-pages):
>> Hello Tom,
>>
>> On 10/22/2011 02:13 PM, Tom Gundersen wrote:
>>> Hi,
>>>
>>> This might not be so much a bug report, as a request for clarification.
>>>
>>> In random(4) it is explained that /proc/sys/kernel/random/poolsize
>>> contains the value in bits or bytes in >=2.6 and 2.4 respectively.
>>> However, the example in the preceding paragraph assumes a 2.4 kernel
>>> is being used, and treats the value as if it were in bytes.
>>>
>>> I ran across this as I maintain the initscripts for Arch Linux, where
>>> we have been (mistakenly) following the example even though we use a
>>> 3.0 kernel. Maybe it would be worthwhile to change the example into
>>> the 2.6 interface, or at least include a word of caution?
>>>
>>> I realise that using a value which is too large, probably does no harm
>>> at all, but not being cryptography expert, I'd rather not take the
>>> chance.
>>
>> Long after the fact... I applied the patch below.
>> Okay?
>>
>> Thanks for the report.
>>
>> Cheers,
>>
>> Michael
>>
>> PS I am going to be in Oslo a couple of times in coming months.
>> Perhaps we could meet up for a beer or so.
>>
>> diff --git a/man4/random.4 b/man4/random.4
>> index 2519981..4a32aac 100644
>> --- a/man4/random.4
>> +++ b/man4/random.4
>> @@ -171,7 +171,7 @@ This reduces the actual amount of noise in the entropy pool
>>  below the estimate.
>>  In order to counteract this effect, it helps to carry
>>  entropy pool information across shut-downs and start-ups.
>> -To do this, add the following lines to an appropriate script
>> +To do this, add the lines to an appropriate script
>>  which is run during the Linux system start-up sequence:
>>  
>>  .nf
>> @@ -186,7 +186,8 @@ which is run during the Linux system start-up sequence:
>>      fi
>>      chmod 600 $random_seed
>>      poolfile=/proc/sys/kernel/random/poolsize
>> -    [ \-r $poolfile ] && bytes=\`cat $poolfile\` || bytes=512
>> +    [ \-r $poolfile ] && bits=\`cat $poolfile\` || bits=4096
> 
> I believe it was end of the 80's when $( ) was introduced to replace \`
> Since this example is for 2.6 maybe it would be useful to use it and
> improve readability ?

Yes, of course, and especially so since I use the modern syntax in the 
new piece that I added. Fixed. Thanks for catching the obvious point
that I missed!

Cheers,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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