Linux中系统参数修改命令sysctl的使用讲解

sysctl配置与显示在/proc/sys目录中的内核参数．可以用sysctl来设置或重新设置联网功能，如IP转发、IP碎片去除以及源路由检查等。用户只需要编辑/etc/sysctl.conf文件，即可手工或自动执行由sysctl控制的功能。

命令格式： sysctl [-n] [-e] -w variable=value sysctl [-n] [-e] -p (default /etc/sysctl.conf) sysctl [-n] [-e] -a 常用参数的意义： -w 临时改变某个指定参数的值，如 sysctl -w net.ipv4.ip_forward=1 -a 显示所有的系统参数 -p 从指定的文件加载系统参数，如不指定即从/etc/sysctl.conf中加载 如果仅仅是想临时改变某个系统参数的值，可以用两种方法来实现,例如想启用IP路由转发功能： 1) #echo 1 > /proc/sys/net/ipv4/ip_forward 2) #sysctl -w net.ipv4.ip_forward=1 以上两种方法都可能立即开启路由功能，但如果系统重启，或执行了 # service network restart命令，所设置的值即会丢失，如果想永久保留配置，可以修改/etc/sysctl.conf文件将 net.ipv4.ip_forward=0改为net.ipv4.ip_forward=1

常见用法

修改(配置)方法有三种临时生效2种

如果系统重启，或执行service network restart命令，所设置的值即会丢失 /proc目录下的所有内容都是临时性的， 所以重启动系统后任何修改都会丢失。 永久生效1种

修改net.ipv4.ip_forward=0的值为1 // 打开数据包的转发功能

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\’)。

实例

sysctl -a所看到的参数全部来自/proc/sys/目录下的文件内容，可以用grep加sort加ll的方法来查看与对应

total 0 dr-xr-xr-x 0 root root 0 Apr 12 14:29 crypto dr-xr-xr-x 0 root root 0 May 10 15:53 debug dr-xr-xr-x 0 root root 0 Apr 12 14:28 dev dr-xr-xr-x 0 root root 0 Apr 12 14:28 fs dr-xr-xr-x 0 root root 0 Apr 12 14:28 kernel dr-xr-xr-x 0 root root 0 Apr 12 14:28 net dr-xr-xr-x 0 root root 0 May 10 15:53 sunrpc dr-xr-xr-x 0 root root 0 May 10 15:53 vm

net.netfilter.nf_conntrack_acct = 1 net.netfilter.nf_conntrack_buckets = 16384 net.netfilter.nf_conntrack_checksum = 1 net.netfilter.nf_conntrack_count = 1739 net.netfilter.nf_conntrack_expect_max = 256 net.netfilter.nf_conntrack_generic_timeout = 600 net.netfilter.nf_conntrack_icmp_timeout = 30 net.netfilter.nf_conntrack_log_invalid = 0 net.netfilter.nf_conntrack_max = 65536 net.netfilter.nf_conntrack_tcp_be_liberal = 0 net.netfilter.nf_conntrack_tcp_loose = 1 net.netfilter.nf_conntrack_tcp_max_retrans = 3 net.netfilter.nf_conntrack_tcp_timeout_close = 10 net.netfilter.nf_conntrack_tcp_timeout_close_wait = 60 net.netfilter.nf_conntrack_tcp_timeout_established = 432000 net.netfilter.nf_conntrack_tcp_timeout_fin_wait = 120 net.netfilter.nf_conntrack_tcp_timeout_last_ack = 30 net.netfilter.nf_conntrack_tcp_timeout_max_retrans = 300 net.netfilter.nf_conntrack_tcp_timeout_syn_recv = 60 net.netfilter.nf_conntrack_tcp_timeout_syn_sent = 120 net.netfilter.nf_conntrack_tcp_timeout_time_wait = 120 net.netfilter.nf_conntrack_tcp_timeout_unacknowledged = 300 net.netfilter.nf_conntrack_udp_timeout = 30 net.netfilter.nf_conntrack_udp_timeout_stream = 180

total 0 -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_acct -r–r–r– 1 root root 0 May 10 15:53 nf_conntrack_buckets -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_checksum -r–r–r– 1 root root 0 May 10 15:53 nf_conntrack_count -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_expect_max -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_generic_timeout -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_icmp_timeout -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_log_invalid -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_max -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_be_liberal -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_loose -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_max_retrans -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_timeout_close -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_timeout_close_wait -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_timeout_established -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_timeout_fin_wait -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_timeout_last_ack -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_timeout_max_retrans -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_timeout_syn_recv -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_timeout_syn_sent -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_timeout_time_wait -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_tcp_timeout_unacknowledged -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_udp_timeout -rw-r–r– 1 root root 0 May 10 15:53 nf_conntrack_udp_timeout_stream

net.core.dev_weight = 64 net.core.message_burst = 10 net.core.message_cost = 5 net.core.netdev_budget = 300 net.core.netdev_max_backlog = 1000 net.core.optmem_max = 10240 net.core.rmem_default = 111616 net.core.rmem_max = 131071 net.core.somaxconn = 8192 net.core.warnings = 1 net.core.wmem_default = 111616 net.core.wmem_max = 131071 net.core.xfrm_acq_expires = 30 net.core.xfrm_aevent_etime = 10 net.core.xfrm_aevent_rseqth = 2 net.core.xfrm_larval_drop = 1

total 0 -rw-r–r– 1 root root 0 May 10 15:53 dev_weight -rw-r–r– 1 root root 0 May 10 15:53 message_burst -rw-r–r– 1 root root 0 May 10 15:53 message_cost -rw-r–r– 1 root root 0 May 10 15:53 netdev_budget -rw-r–r– 1 root root 0 May 10 15:53 netdev_max_backlog -rw-r–r– 1 root root 0 May 10 15:53 optmem_max -rw-r–r– 1 root root 0 May 10 15:53 rmem_default -rw-r–r– 1 root root 0 May 10 15:53 rmem_max -rw-r–r– 1 root root 0 Apr 12 14:29 somaxconn -rw-r–r– 1 root root 0 May 10 15:53 warnings -rw-r–r– 1 root root 0 May 10 15:53 wmem_default -rw-r–r– 1 root root 0 May 10 15:53 wmem_max -rw-r–r– 1 root root 0 May 10 15:53 xfrm_acq_expires -rw-r–r– 1 root root 0 May 10 15:53 xfrm_aevent_etime -rw-r–r– 1 root root 0 May 10 15:53 xfrm_aevent_rseqth -rw-r–r– 1 root root 0 May 10 15:53 xfrm_larval_drop