原文：https://blog.csdn.net/u012707739/article/details/78254241

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，用sysctl可以读取设置超过五百个系统变量。

sysctl命令

用法： 
sysctl [options] [variable[=value] …]

常用选项： 
-n：打印时只打印值，不打印参数名称； 
-e：忽略未知关键字错误； 
-N：打印时只打印参数名称，不打印值； 
-w：设置参数的值（不过好像不加这个选项也可以直接设置）； 
-p：从配置文件“/etc/sysctl.conf”加载内核参数设置； 
-a：打印所有内核参数变量； 
-A：以表格方式打印所有内核参数变量。

示例

1、 设置socket接收缓冲最大值（rmem_max）为212992字节

sudo sysctl -w net.core.rmem_max=212992

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2、查看socket接收缓冲最大值（rmem_max）

sysctl net.core.rmem_max

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sysctl可以设置查看的内核参数都在目录/proc/sys中，每个文件都记录了一个参数，sysctl命令中其实也记录了参数的相对路径，只要将 . 换成 / 就是文件路径，比如记录net.core.rmem_max的文件就是/proc/sys/net/core/rmem_max，所以也可以直接查看文件内容来读取参数的值

cat /proc/sys/net/core/rmem_max

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如果不知道参数路径也可以这么做：

sysctl -a | grep rmem_max

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配置sysctl

编辑此文件vi /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（复制自http://man.linuxde.net/sysctl）：

# Controls source route verification
# Default should work for all interfaces
net.ipv4.conf.default.rp_filter = 1 # net.ipv4.conf.all.rp_filter = 1 # net.ipv4.conf.lo.rp_filter = 1 # net.ipv4.conf.eth0.rp_filter = 1 # Disables IP source routing # Default should work for all interfaces net.ipv4.conf.default.accept_source_route = 0 # net.ipv4.conf.all.accept_source_route = 0 # net.ipv4.conf.lo.accept_source_route = 0 # net.ipv4.conf.eth0.accept_source_route = 0 # Controls the System Request debugging functionality of the kernel kernel.sysrq = 0 # Controls whether core dumps will append the PID to the core filename. # Useful for debugging multi-threaded applications. kernel.core_uses_pid = 1 # Increase maximum amount of memory allocated to shm # Only uncomment if needed! # kernel.shmmax = 67108864 # Disable ICMP Redirect Acceptance # Default should work for all interfaces net.ipv4.conf.default.accept_redirects = 0 # net.ipv4.conf.all.accept_redirects = 0 # net.ipv4.conf.lo.accept_redirects = 0 # net.ipv4.conf.eth0.accept_redirects = 0 # Enable Log Spoofed Packets, Source Routed Packets, Redirect Packets # Default should work for all interfaces net.ipv4.conf.default.log_martians = 1 # net.ipv4.conf.all.log_martians = 1 # net.ipv4.conf.lo.log_martians = 1 # net.ipv4.conf.eth0.log_martians = 1 # Decrease the time default value for tcp_fin_timeout connection net.ipv4.tcp_fin_timeout = 25 # Decrease the time default value for tcp_keepalive_time connection net.ipv4.tcp_keepalive_time = 1200 # Turn on the tcp_window_scaling net.ipv4.tcp_window_scaling = 1 # Turn on the tcp_sack net.ipv4.tcp_sack = 1 # tcp_fack should be on because of sack net.ipv4.tcp_fack = 1 # Turn on the tcp_timestamps net.ipv4.tcp_timestamps = 1 # Enable TCP SYN Cookie Protection net.ipv4.tcp_syncookies = 1 # Enable ignoring broadcasts request net.ipv4.icmp_echo_ignore_broadcasts = 1 # Enable bad error message Protection net.ipv4.icmp_ignore_bogus_error_responses = 1 # Make more local ports available # net.ipv4.ip_local_port_range = 1024 65000 # Set TCP Re-Ordering value in kernel to ‘5′ net.ipv4.tcp_reordering = 5 # Lower syn retry rates net.ipv4.tcp_synack_retries = 2 net.ipv4.tcp_syn_retries = 3 # Set Max SYN Backlog to ‘2048′ net.ipv4.tcp_max_syn_backlog = 2048 # Various Settings net.core.netdev_max_backlog = 1024 # Increase the maximum number of skb-heads to be cached net.core.hot_list_length = 256 # Increase the tcp-time-wait buckets pool size net.ipv4.tcp_max_tw_buckets = 360000 # This will increase the amount of memory available for socket input/output queues net.core.rmem_default = 65535 net.core.rmem_max = 8388608 net.ipv4.tcp_rmem = 4096 87380 8388608 net.core.wmem_default = 65535 net.core.wmem_max = 8388608 net.ipv4.tcp_wmem = 4096 65535 8388608 net.ipv4.tcp_mem = 8388608 8388608 8388608 net.core.optmem_max = 40960

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如果希望屏蔽别人 ping 你的主机，则加入以下代码：

# Disable ping requests
net.ipv4.icmp_echo_ignore_all = 1

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编辑完成后，请执行以下命令使变动立即生效：

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

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TCP/IP参数

所有的TCP/IP参数都位于/proc/sys/net目录下（请注意，对/proc/sys/net目录下内容的修改都是临时的，任何修改在系统重启后都会丢失），例如下面这些重要的参数：