AHMED ZBYR

AHMED ZBYR

Biker, EV Enthusiast

Performace tuning Hadoop at kernel level. sysctl is an interface that allows you to make changes to a running Linux kernel. With /etc/sysctl.conf you can configure various Linux networking and system settings such as:

  • Limit network-transmitted configuration for IPv4
  • Limit network-transmitted configuration for IPv6
  • Turn on execshield protection
  • Prevent against the common syn flood attack
  • Turn on source IP address verification
  • Prevents a cracker from using a spoofing attack against the IP address of the server.
  • Logs several types of suspicious packets, such as spoofed packets, source-routed packets, and redirects.

File System

  1. fs.file-max Increase size of file handles and inode cache
[ahmed@server ~]# echo 'fs.file-max = 943718' >> /etc/sysctl.conf

Swappiness

Do less swapping

  1. vm.dirty_ratio setting virtual memory ratio.
  2. vm.swappiness How often swap should be used. 0 is least, 60 default.
[ahmed@server ~]# echo 'vm.dirty_ratio=10' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'vm.swappiness=0' >> /etc/sysctl.conf

Connection Settings

  1. net.core.netdev_max_backlog Increase number of incoming connections backlog.
  2. net.core.somaxconn Increase number of incoming connections.
[ahmed@server ~]# echo 'net.core.netdev_max_backlog = 4000' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.core.somaxconn = 4000' >> /etc/sysctl.conf

TCP settings

  1. net.ipv4.tcp_sack Disable select acknowledgments
  2. net.ipv4.tcp_dsack Allows TCP to send “duplicate” SACKs.
  3. net.ipv4.tcp_keepalive_time How often TCP sends out keepalive messages when keepalive is enabled. Default: 2hours.
  4. net.ipv4.tcp_keepalive_probes How many keepalive probes TCP sends out, until it decides that the connection is broken. Default value: 9.
  5. net.ipv4.tcp_keepalive_intvl How frequently the probes are send out. Multiplied by tcp_keepalive_probes it is time to kill not responding connection, after probes started. Default value: 75sec i.e. connection will be aborted after ~11 minutes of retries.
  6. net.ipv4.tcp_fin_timeout Time to hold socket in state FIN-WAIT-2, if it was closed by our side. Peer can be broken and never close its side, or even died unexpectedly. Default value is 60sec. Usual value used in 2.2 was 180 seconds, you may restore it, but remember that if your machine is even underloaded WEB server, you risk to overflow memory with kilotons of dead sockets, FIN-WAIT-2 sockets are less dangerous than FIN-WAIT-1, because they eat maximum 1.5K of memory, but they tend to live longer. Cf.tcp_max_orphans.
  7. net.ipv4.tcp_rmem The three values setting the minimum, initial, and maximum size of the Memory Receive Buffer per connection. They define the actual memory usage, not just TCP window size.
  8. net.ipv4.tcp_wmem The same as tcp_rmem, but just for Memory Send Buffer per connection.
  9. net.ipv4.tcp_retries2 This value influences the timeout of an alive TCP connection, when RTO retransmissions remain unacknowledged. Given a value of N, a hypothetical TCP connection following exponential backoff with an initial RTO of TCP_RTO_MIN would retransmit N times before killing the connection at the (N+1)th RTO. The default value of 15 yields a hypothetical timeout of 924.6 seconds and is a lower bound for the effective timeout. TCP will effectively time out at the first RTO which exceeds the hypothetical timeout. RFC 1122 recommends at least 100 seconds for the timeout, which corresponds to a value of at least 8.
  10. net.ipv4.tcp_synack_retries Number of times SYNACKs for a passive TCP connection attempt will be retransmitted. Should not be higher than 255. Default value is 5, which corresponds to ~180seconds.
[ahmed@server ~]# echo 'net.ipv4.tcp_sack = 0' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.ipv4.tcp_dsack = 0' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.ipv4.tcp_keepalive_time = 600' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.ipv4.tcp_keepalive_probes = 5' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.ipv4.tcp_keepalive_intvl = 15' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.ipv4.tcp_fin_timeout = 30' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.ipv4.tcp_rmem = 32768 436600 4194304' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.ipv4.tcp_wmem = 32768 436600 4194304' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.ipv4.tcp_retries2 = 10' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.ipv4.tcp_synack_retries = 3' >> /etc/sysctl.conf

Disable IPv6 Defaults. We dont use these anyway.

[ahmed@server ~]# echo 'net.ipv6.conf.all.disable_ipv6 = 1' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.ipv6.conf.default.disable_ipv6 = 1' >> /etc/sysctl.conf
[ahmed@server ~]# echo 'net.ipv6.conf.lo.disable_ipv6 = 1' >> /etc/sysctl.conf

Execute below command to make it permanent.

[ahmed@server ~]# sysctl -p

Next update limits.

[ahmed@server ~]# echo '* - nofile 65536' >>/etc/security/limits.conf
[ahmed@server ~]# echo '* - nproc 65536' >>/etc/security/limits.conf

More Details on IPv4

  • http://www.cyberciti.biz/files/linux-kernel/Documentation/networking/ip-sysctl.txt
  • http://www.cyberciti.biz/files/linux-kernel/Documentation/sysctl/

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