I just installed centos 6.3 freshly and noticed the following:

[root@localhost user1]# cat /etc/redhat-release CentOS release 6.3 (Final)

[root@localhost user1]#

[root@localhost user1]# cat /proc/sys/net/core/rmem_max 131071

[root@localhost user1]# cat /proc/sys/net/core/rmem_default 229376

[root@localhost user1]# cat /proc/sys/net/core/wmem_max 131071

[root@localhost user1]# cat /proc/sys/net/core/wmem_default 229376

As you can see rmem_max is "Lesser " than rmem_default and wmem_max is "Lesser" than wmem_default.

As per my knowledge wmem_max and rmem_max should be more than default values ?


# cat /etc/redhat-release CentOS release 6.3 (Final)

# uname -a Linux localhost.localdomain 2.6.32-279.el6.x86_64 #1 SMP Fri Jun 22 12:19:21 UTC 2012 x86_64 x86_64 x86_64 GNU/Linux

<< link : https://access.redhat.com/site/documentation/en-US/Red_Hat_Enterprise_Linux/7-Beta/html/Performance_Tuning_Guide/s-network-dont-adjust-defaults.html

Bear in mind that the value of rmem_default should be no greater than rmem_max (/proc/sys/net/core/rmem_max); if need be, increase the value of rmem_max.

  • paste 'uname -a' – Danila Ladner Jan 20 '14 at 14:32
  • updated kernel version.. – kumar Jan 22 '14 at 6:17

if it is "2.6.32-279" then it is a bug, upgrade it. Should be either equal or more as you mentioned in the link.

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  • Thanks!..As you mentioned in your Answer, it is 2.6.32-279 only. I see some weird behaviour with UDP burst traffic with these settings..It may be due to these numbers. If you have any additional info. please let me know. – kumar Jan 22 '14 at 6:15
  • Yes ,because buffers get overflown, upgrade, do not use this kernel, upgrade to 6.4 there is no such thing there, i am not sure where this bug came from in this x.y.z ver – Danila Ladner Jan 22 '14 at 6:25
  • unfortunately I do not have the luxury to upgrade the kernel..rather, I need to figure out why this is happening..anyway Thanks. – kumar Jan 22 '14 at 6:39
  • Well then change it to 229376 for {w,r}mem_max and see if you experience the busrts – Danila Ladner Jan 22 '14 at 6:41

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