Difference between revisions of "Talk:Sysctl"

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(Virtual memory: re, close)
 
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I can't imagine this being a very long article, but I do find it useful. I didn't have a clue what this command did until I came across it now. I recall it from my first time installing Arch, with regard to storing the volume levels in alsamixer. --[[User:Mustard|Mustard]] 10:31, 22 October 2010 (EDT)
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== net.ipv4.tcp_rfc1337 ==
  
error: permission denied on key 'net.ipv4.conf.all.mc_forwarding'
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From [https://www.kernel.org/doc/Documentation/networking/ip-sysctl.txt kernel doc]:
error: permission denied on key 'net.ipv4.conf.default.mc_forwarding'
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Are these not used any-more?
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{{bc|
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tcp_rfc1337 - BOOLEAN
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If set, the TCP stack behaves conforming to RFC1337. If unset,
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we are not conforming to RFC, but prevent TCP TIME_WAIT
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assassination.
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Default: 0
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}}
  
:it's read only which might mean that it has to be changed while compiling the kernel, I'm not sure (it used to work), it is disabled by default anyway [[User:Thestinger|thestinger]] 16:39, 26 October 2010 (EDT)
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So, isn't {{ic|0}} the safe value? Our wiki says otherwise. -- [[User:Lahwaacz|Lahwaacz]] ([[User talk:Lahwaacz|talk]]) 08:56, 17 September 2013 (UTC)
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:With setting {{ic|0}} the system would 'assassinate' a socket in time_wait prematurely upon receiving a RST. While this might sound like a good idea (it frees up a socket quicker), it opens the door for tcp sequence problems/syn replay. Those problems were described in RFC1337 and enabling the setting {{ic|1}} is one way to deal with them (letting TIME_WAIT packets idle out even if a reset is received, so that the sequence number cannot be reused meanwhile). The wiki is correct in my view. <s>Kernel doc is wrong here - "prevent" should read "enable".</s>  --[[User:Indigo|Indigo]] ([[User talk:Indigo|talk]]) 21:12, 17 September 2013 (UTC)
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== <s>Virtual memory</s> ==
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[https://www.kernel.org/doc/Documentation/sysctl/vm.txt| Documentation] has changed::
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{{bc|
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dirty_ratio
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Contains, as a percentage of total available memory that contains free pages
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and reclaimable pages, the number of pages at which a process which is
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generating disk writes will itself start writing out dirty data.
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The total available memory is not equal to total system memory.}}
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{{bc|
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dirty_background_ratio
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Contains, as a percentage of total available memory that contains free pages
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and reclaimable pages, the number of pages at which the background kernel
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flusher threads will start writing out dirty data.
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The total available memory is not equal to total system memory.
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}}
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: -[[User:Tsester|Tsester]] ([[User talk:Tsester|talk]]) 21:27, 16 May 2016 (UTC)
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:Hm, the quote might have been shortened before to keep it simple before the example calculation. Anyhow, updated it with [https://wiki.archlinux.org/index.php?title=Sysctl&type=revision&diff=435334&oldid=422169], thanks. --[[User:Indigo|Indigo]] ([[User talk:Indigo|talk]]) 18:53, 17 May 2016 (UTC)

Latest revision as of 18:53, 17 May 2016

net.ipv4.tcp_rfc1337

From kernel doc:

tcp_rfc1337 - BOOLEAN
	If set, the TCP stack behaves conforming to RFC1337. If unset,
	we are not conforming to RFC, but prevent TCP TIME_WAIT
	assassination.
	Default: 0

So, isn't 0 the safe value? Our wiki says otherwise. -- Lahwaacz (talk) 08:56, 17 September 2013 (UTC)

With setting 0 the system would 'assassinate' a socket in time_wait prematurely upon receiving a RST. While this might sound like a good idea (it frees up a socket quicker), it opens the door for tcp sequence problems/syn replay. Those problems were described in RFC1337 and enabling the setting 1 is one way to deal with them (letting TIME_WAIT packets idle out even if a reset is received, so that the sequence number cannot be reused meanwhile). The wiki is correct in my view. Kernel doc is wrong here - "prevent" should read "enable". --Indigo (talk) 21:12, 17 September 2013 (UTC)

Virtual memory

Documentation has changed::


dirty_ratio

Contains, as a percentage of total available memory that contains free pages
and reclaimable pages, the number of pages at which a process which is
generating disk writes will itself start writing out dirty data.

The total available memory is not equal to total system memory.
dirty_background_ratio

Contains, as a percentage of total available memory that contains free pages
and reclaimable pages, the number of pages at which the background kernel
flusher threads will start writing out dirty data.

The total available memory is not equal to total system memory.
-Tsester (talk) 21:27, 16 May 2016 (UTC)
Hm, the quote might have been shortened before to keep it simple before the example calculation. Anyhow, updated it with [1], thanks. --Indigo (talk) 18:53, 17 May 2016 (UTC)