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146 lines
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146 lines
6.0 KiB
HTML
<h1 id="sysctl">sysctl</h1>
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<p>时动态地修改内核的运行参数</p>
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<h2 id="补充说明">补充说明</h2>
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<p><strong>sysctl命令</strong> 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<code>/proc/sys</code>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。</p>
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<h3 id="语法">语法</h3>
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<pre><code class="language-bash">sysctl(选项)(参数)</code></pre>
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<h3 id="选项">选项</h3>
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<pre><code class="language-bash">-n：打印值时不打印关键字；
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-e：忽略未知关键字错误；
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-N：仅打印名称；
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-w：当改变sysctl设置时使用此项；
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-p：从配置文件“/etc/sysctl.conf”加载内核参数设置；
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-a：打印当前所有可用的内核参数变量和值；
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-A：以表格方式打印当前所有可用的内核参数变量和值。</code></pre>
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<h3 id="参数">参数</h3>
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<p>变量=值：设置内核参数对应的变量值。</p>
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<h3 id="实例">实例</h3>
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<p>查看所有可读变量：</p>
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<p>sysctl -a</p>
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<p>读一个指定的变量，例如<code>kern.maxproc</code>：</p>
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<p>sysctl kern.maxproc kern.maxproc: 1044</p>
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<p>要设置一个指定的变量，直接用<code>variable=value</code>这样的语法：</p>
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<pre><code class="language-bash">sysctl kern.maxfiles=5000
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kern.maxfiles: 2088 -> 5000</code></pre>
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<p>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<code>variable=value</code>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。</p>
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<p>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’）。</p>
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<pre><code class="language-bash">sysctl -w kernel.sysrq=0
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sysctl -w kernel.core_uses_pid=1
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sysctl -w net.ipv4.conf.default.accept_redirects=0
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sysctl -w net.ipv4.conf.default.accept_source_route=0
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sysctl -w net.ipv4.conf.default.rp_filter=1
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sysctl -w net.ipv4.tcp_syncookies=1
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sysctl -w net.ipv4.tcp_max_syn_backlog=2048
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sysctl -w net.ipv4.tcp_fin_timeout=30
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sysctl -w net.ipv4.tcp_synack_retries=2
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sysctl -w net.ipv4.tcp_keepalive_time=3600
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sysctl -w net.ipv4.tcp_window_scaling=1
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sysctl -w net.ipv4.tcp_sack=1</code></pre>
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<h3 id="配置sysctl">配置sysctl</h3>
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<p>编辑此文件：<code>/etc/sysctl.conf</code></p>
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<p>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：</p>
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<pre><code class="language-bash"># Controls source route verification
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# Default should work for all interfaces
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net.ipv4.conf.default.rp_filter = 1
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# net.ipv4.conf.all.rp_filter = 1
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# net.ipv4.conf.lo.rp_filter = 1
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# net.ipv4.conf.eth0.rp_filter = 1
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# Disables IP source routing
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# Default should work for all interfaces
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net.ipv4.conf.default.accept_source_route = 0
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# net.ipv4.conf.all.accept_source_route = 0
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# net.ipv4.conf.lo.accept_source_route = 0
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# net.ipv4.conf.eth0.accept_source_route = 0
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# Controls the System Request debugging functionality of the kernel
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kernel.sysrq = 0
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# Controls whether core dumps will append the PID to the core filename.
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# Useful for debugging multi-threaded applications.
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kernel.core_uses_pid = 1
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# Increase maximum amount of memory allocated to shm
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# Only uncomment if needed!
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# kernel.shmmax = 67108864
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# Disable ICMP Redirect Acceptance
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# Default should work for all interfaces
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net.ipv4.conf.default.accept_redirects = 0
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# net.ipv4.conf.all.accept_redirects = 0
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# net.ipv4.conf.lo.accept_redirects = 0
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# net.ipv4.conf.eth0.accept_redirects = 0
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# enable Log Spoofed Packets, Source Routed Packets, Redirect Packets
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# Default should work for all interfaces
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net.ipv4.conf.default.log_martians = 1
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# net.ipv4.conf.all.log_martians = 1
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# net.ipv4.conf.lo.log_martians = 1
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# net.ipv4.conf.eth0.log_martians = 1
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# Decrease the time default value for tcp_fin_timeout connection
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net.ipv4.tcp_fin_timeout = 25
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# Decrease the time default value for tcp_keepalive_time connection
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net.ipv4.tcp_keepalive_time = 1200
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# Turn on the tcp_window_scaling
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net.ipv4.tcp_window_scaling = 1
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# Turn on the tcp_sack
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net.ipv4.tcp_sack = 1
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# tcp_fack should be on because of sack
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net.ipv4.tcp_fack = 1
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# Turn on the tcp_timestamps
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net.ipv4.tcp_timestamps = 1
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# Enable TCP SYN Cookie Protection
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net.ipv4.tcp_syncookies = 1
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# Enable ignoring broadcasts request
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net.ipv4.icmp_echo_ignore_broadcasts = 1
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# Enable bad error message Protection
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net.ipv4.icmp_ignore_bogus_error_responses = 1
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# make more local ports available
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# net.ipv4.ip_local_port_range = 1024 65000
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# set TCP Re-Ordering value in kernel to ‘5′
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net.ipv4.tcp_reordering = 5
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# Lower syn retry rates
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net.ipv4.tcp_synack_retries = 2
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net.ipv4.tcp_syn_retries = 3
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# Set Max SYN Backlog to ‘2048′
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net.ipv4.tcp_max_syn_backlog = 2048
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# Various Settings
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net.core.netdev_max_backlog = 1024
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# Increase the maximum number of skb-heads to be cached
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net.core.hot_list_length = 256
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# Increase the tcp-time-wait buckets pool size
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net.ipv4.tcp_max_tw_buckets = 360000
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# This will increase the amount of memory available for socket input/output queues
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net.core.rmem_default = 65535
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net.core.rmem_max = 8388608
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net.ipv4.tcp_rmem = 4096 87380 8388608
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net.core.wmem_default = 65535
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net.core.wmem_max = 8388608
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net.ipv4.tcp_wmem = 4096 65535 8388608
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net.ipv4.tcp_mem = 8388608 8388608 8388608
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net.core.optmem_max = 40960</code></pre>
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<p>如果希望屏蔽别人 ping 你的主机，则加入以下代码：</p>
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<pre><code class="language-bash"># Disable ping requests
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net.ipv4.icmp_echo_ignore_all = 1</code></pre>
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<p>编辑完成后，请执行以下命令使变动立即生效：</p>
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<pre><code class="language-bash">/sbin/sysctl -p
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/sbin/sysctl -w net.ipv4.route.flush=1</code></pre>
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