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sysctl
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===
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时动态地修改内核的运行参数
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## 说明
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**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。
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### 语法
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```
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sysctl(选项)(参数)
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```
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```
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-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。
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```
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### 参数
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变量=值:设置内核参数对应的变量值。
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### 实例
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查看所有可读变量:
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sysctl -a
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读一个指定的变量,例如`kern.maxproc`:
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sysctl kern.maxproc kern.maxproc: 1044
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要设置一个指定的变量,直接用`variable=value`这样的语法:
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```
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sysctl kern.maxfiles=5000
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kern.maxfiles: 2088 -> 5000
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```
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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。
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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')。
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```
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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
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```
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### 配置sysctl
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编辑此文件:`/etc/sysctl.conf`
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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:
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```
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# 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
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```
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如果希望屏蔽别人 ping 你的主机,则加入以下代码:
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```
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# Disable ping requests
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net.ipv4.icmp_echo_ignore_all = 1
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```
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编辑完成后,请执行以下命令使变动立即生效:
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```
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/sbin/sysctl -p
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/sbin/sysctl -w net.ipv4.route.flush=1
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```
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