• sysctl
    • 补充说明
      • 语法
      • 选项
      • 参数
      • 实例
      • 配置sysctl

    sysctl

    时动态地修改内核的运行参数

    补充说明

    sysctl命令 被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， 这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。

    语法

    1. sysctl(选项)(参数)

    选项

    1. -n：打印值时不打印关键字；
    2. -e：忽略未知关键字错误；
    3. -N：仅打印名称；
    4. -w：当改变sysctl设置时使用此项；
    5. -p：从配置文件“/etc/sysctl.conf”加载内核参数设置；
    6. -a：打印当前所有可用的内核参数变量和值；
    7. -A：以表格方式打印当前所有可用的内核参数变量和值。

    参数

    变量=值：设置内核参数对应的变量值。

    实例

    查看所有可读变量：

    sysctl -a

    读一个指定的变量，例如kern.maxproc：

    sysctl kern.maxproc kern.maxproc: 1044

    要设置一个指定的变量，直接用variable=value这样的语法：

    1. sysctl kern.maxfiles=5000
    2. kern.maxfiles: 2088 -> 5000

    您可以使用sysctl修改系统变量，也可以通过编辑sysctl.conf文件来修改系统变量。sysctl.conf看起来很像rc.conf。它用variable=value的形式来设定值。指定的值在系统进入多用户模式之后被设定。并不是所有的变量都可以在这个模式下设定。

    sysctl变量的设置通常是字符串、数字或者布尔型。（布尔型用 1 来表示’yes’，用 0 来表示’no’）。

    1. sysctl -w kernel.sysrq=0
    2. sysctl -w kernel.core_uses_pid=1
    3. sysctl -w net.ipv4.conf.default.accept_redirects=0
    4. sysctl -w net.ipv4.conf.default.accept_source_route=0
    5. sysctl -w net.ipv4.conf.default.rp_filter=1
    6. sysctl -w net.ipv4.tcp_syncookies=1
    7. sysctl -w net.ipv4.tcp_max_syn_backlog=2048
    8. sysctl -w net.ipv4.tcp_fin_timeout=30
    9. sysctl -w net.ipv4.tcp_synack_retries=2
    10. sysctl -w net.ipv4.tcp_keepalive_time=3600
    11. sysctl -w net.ipv4.tcp_window_scaling=1
    12. sysctl -w net.ipv4.tcp_sack=1

    配置sysctl

    编辑此文件：/etc/sysctl.conf

    如果该文件为空，则输入以下内容，否则请根据情况自己做调整：

    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

    如果希望屏蔽别人 ping 你的主机，则加入以下代码：

    1. # Disable ping requests
    2. net.ipv4.icmp_echo_ignore_all = 1

    编辑完成后，请执行以下命令使变动立即生效：

    1. /sbin/sysctl -p
    2. /sbin/sysctl -w net.ipv4.route.flush=1