sysctl命令用于在内核运行时动态地修改内核的运行参数。
可用的内核参数在目录/proc/sys中。它包含一些TCP/ip堆栈和虚拟内存系统的高级选项。
可以让有经验的管理员提高引人注目的系统性能。用sysctl可以读取设置超过五百个系统变量。

用法

sysctl [选项] [variable[=value] …]
sysctl 选项并不多，常用的可能也就下面几个：

  1.   -a, --all            display all variables 显示所有变量
  2.   -N, --names          print variable names without values 打印变量名但不现实值
  3.   -p, --load[=<file>]  read values from file 从文件加载参数值，默认是从 /etc/sysctl.conf
  4.   -w, --write          enable writing a value to variable 改变当前sysctl设置
  5.   -h, --help                 display this help and exit 显示帮助

要列出所有参数，使用
# sysctl -a

永久配置参数：
# sysctl -w .= >> /etc/sysctl.conf

重启机器以使更改生效，如不要重启可以执行以下命令立即加载：
# sysctl -p /etc/sysctl.d/*.conf
或
# sysctl -p 直接加载默认配置文件

常见可调整参数：

  1. # Controls source route verification
  2. # Default should work for all interfaces
  3. net.ipv4.conf.default.rp_filter = 1
  4. # net.ipv4.conf.all.rp_filter = 1
  5. # net.ipv4.conf.lo.rp_filter = 1
  6. # net.ipv4.conf.eth0.rp_filter = 1
  8. # Disables IP source routing
  9. # Default should work for all interfaces
  10. net.ipv4.conf.default.accept_source_route = 0
  11. # net.ipv4.conf.all.accept_source_route = 0
  12. # net.ipv4.conf.lo.accept_source_route = 0
  13. # net.ipv4.conf.eth0.accept_source_route = 0
  15. # Controls the System Request debugging functionality of the kernel
  16. kernel.sysrq = 0
  18. # Controls whether core dumps will append the PID to the core filename.
  19. # Useful for debugging multi-threaded applications.
  20. kernel.core_uses_pid = 1
  22. # Increase maximum amount of memory allocated to shm
  23. # Only uncomment if needed!
  24. # kernel.shmmax = 67108864
  26. # Disable ICMP Redirect Acceptance
  27. # Default should work for all interfaces
  28. net.ipv4.conf.default.accept_redirects = 0
  29. # net.ipv4.conf.all.accept_redirects = 0
  30. # net.ipv4.conf.lo.accept_redirects = 0
  31. # net.ipv4.conf.eth0.accept_redirects = 0
  33. # enable Log Spoofed Packets, Source Routed Packets, Redirect Packets
  34. # Default should work for all interfaces
  35. net.ipv4.conf.default.log_martians = 1
  36. # net.ipv4.conf.all.log_martians = 1
  37. # net.ipv4.conf.lo.log_martians = 1
  38. # net.ipv4.conf.eth0.log_martians = 1
  40. # Decrease the time default value for tcp_fin_timeout connection
  41. net.ipv4.tcp_fin_timeout = 25
  43. # Decrease the time default value for tcp_keepalive_time connection
  44. net.ipv4.tcp_keepalive_time = 1200
  46. # Turn on the tcp_window_scaling
  47. net.ipv4.tcp_window_scaling = 1
  49. # Turn on the tcp_sack
  50. net.ipv4.tcp_sack = 1
  52. # tcp_fack should be on because of sack
  53. net.ipv4.tcp_fack = 1
  55. # Turn on the tcp_timestamps
  56. net.ipv4.tcp_timestamps = 1
  58. # Enable TCP SYN Cookie Protection
  59. net.ipv4.tcp_syncookies = 1
  61. # Enable ignoring broadcasts request
  62. net.ipv4.icmp_echo_ignore_broadcasts = 1
  64. # Enable bad error message Protection
  65. net.ipv4.icmp_ignore_bogus_error_responses = 1
  67. # make more local ports available
  68. # net.ipv4.ip_local_port_range = 1024 65000
  70. # set TCP Re-Ordering value in kernel to ‘5′
  71. net.ipv4.tcp_reordering = 5
  73. # Lower syn retry rates
  74. net.ipv4.tcp_synack_retries = 2
  75. net.ipv4.tcp_syn_retries = 3
  77. # Set Max SYN Backlog to ‘2048′
  78. net.ipv4.tcp_max_syn_backlog = 2048
  80. # Various Settings
  81. net.core.netdev_max_backlog = 1024
  83. # Increase the maximum number of skb-heads to be cached
  84. net.core.hot_list_length = 256
  86. # Increase the tcp-time-wait buckets pool size
  87. net.ipv4.tcp_max_tw_buckets = 360000
  89. # This will increase the amount of memory available for socket input/output queues
  90. net.core.rmem_default = 65535
  91. net.core.rmem_max = 8388608
  92. net.ipv4.tcp_rmem = 4096 87380 8388608
  93. net.core.wmem_default = 65535
  94. net.core.wmem_max = 8388608
  95. net.ipv4.tcp_wmem = 4096 65535 8388608
  96. net.ipv4.tcp_mem = 8388608 8388608 8388608
  97. net.core.optmem_max = 40960
  99. # Disable ping requests
  100. net.ipv4.icmp_echo_ignore_all = 1