用sysctl调整linux内核参数

sysctl是一个允许您改变正在运行中的Linux系统的接口。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。基于这点，sysctl(8) 提供两个功能：读取和修改系统设置。 常用 查看所有可读变量： [xt@butbueatiful ~] sysctl -a 读一个指定的变量，例如 kernel.msgmnb： [xt@butbueatiful ~]$ sysctl kernel.msgmnb kern.maxproc: 65536 要设置一个指定的变量，直接用 variable=value 这样的语法： [xt@butbueatiful ~]$ sudo sysctl kernel.msgmnb=1024 kernel.msgmnb: 1024 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')。 sysctl -w kernel.sysrq=0 sysctl -w kernel.core_uses_pid=1 sysctl -w net.ipv4.conf.default.accept_redirects=0 sysctl -w net.ipv4.conf.default.accept_source_route=0 sysctl -w net.ipv4.conf.default.rp_filter=1 sysctl -w net.ipv4.tcp_syncookies=1 sysctl -w net.ipv4.tcp_max_syn_backlog=2048 sysctl -w net.ipv4.tcp_fin_timeout=30 sysctl -w net.ipv4.tcp_synack_retries=2 sysctl -w net.ipv4.tcp_keepalive_time=3600 sysctl -w net.ipv4.tcp_window_scaling=1 sysctl -w net.ipv4.tcp_sack=1 配置sysctl [root@butbueatiful ~] 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： # 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 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 执行以下命令使变动立即生效： /sbin/sysctl -p /sbin/sysctl -w net.ipv4.route.flush=1 我们常常在 Linux 的 /proc/sys 目录下,手动设定一些 kernel 的参数或是直接 echo 特定的值给一个 proc下的虚拟档案,俾利某些档案之开启,常见的例如设定开机时自动启动 IP Forwarding: echo “1” > /proc/sys/net/ipv4/ip_forward 其实,在 Linux 我们还可以用 sysctl command 便可以简易的去检视、设定或自动配置特定的 kernel 设定。我们可以在系统提示符号下输入「sysctl -a」 sysctl 的表示法乃把目录结构的「/」以「.」表示,一层一层的连结下去。当然以echo 特定的值给一个 proc下的虚拟档案也是可以用 sysctl加以表示,例如: #sysctl –w net.ipv4.ip_forward =”1” 或是直接在 /etc/sysctl.conf 增删修改特定档案的 0,1值亦可:　 # Enables packet forwarding net.ipv4.ip_forward = 1 # Enables source route verification net.ipv4.conf.default.rp_filter = 1 # Disables the magic-sysrq key kernel.sysrq = 0 当然如果考虑 reboot 后仍有效, 直接在 /etc/sysctl.conf 增删修改特定档案的 0,1值才可使之保留设定(以RedHat 为例,每次开机系统启动后, init 会执行 /etc/rc.d/rc.sysinit,便会使用 /etc/sysctl.conf 的预设值去执行 sysctl)