sysctl下令详解

sysctl命令详解
? sysctl设置和显示在/proc/sys目录中的内核参数．能用sysctl来设置或重新设置连网功能，如IP转发、IP碎片去除及源路由检查等。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=valuesysctl [-n] [-e] -p  (default /etc/sysctl.conf)sysctl [-n] [-e] -a

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常用参数的意义：
-w? ?临时改动某个指定参数的值，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动某个系统参数的值，能用两种方法来实现,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即时开启路由功能，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，如果想永久保留设置，能修改/etc/sysctl.conf文件
将 net.ipv4.ip_forward=0改为net.ipv4.ip_forward=1

**********************sysctl man pageNAMEsysctl - configure kernel parameters at runtimeSYNOPSISsysctl [-n] [-e] variable ...sysctl [-n] [-e] [-q] -w variable=value ...sysctl [-n] [-e] [-q] -p sysctl [-n] [-e] -asysctl [-n] [-e] -ADESCRIPTIONsysctl  is used to modify kernel parameters at runtime.    The parametersavailable are those listed under /proc/sys/.  Procfs  is     required  forsysctl(8)  support  in  Linux.    You can use sysctl(8) to both read andwrite sysctl data.PARAMETERSvariableThe name of a key to read from.  An  example  is    kernel.ostype.The ’/’ separator is also accepted in place of a ’.’.variable=valueTo set a key, use the form variable=value, where variable is thekey and value is the value to set it to.    If the value  containsquotes or characters which are parsed by the shell, you may needto enclose the value in double quotes.   This  requires  the  -wparameter to use.-n     Use  this option to disable printing of the key name when print-ing values.-e     Use this option to ignore errors about unknown keys.-N     Use this option to only print the names. It may be  useful  withshells that have programmable completion.-q     Use this option to not display the values set to stdout.-w     Use this option when you want to change a sysctl setting.-p     Load   in      sysctl   settings   from   the   file     specified  or/etc/sysctl.conf if none given.  Specifying - as filename     meansreading data from standard input.-a     Display all values currently available.-A     Display all values currently available in table form.EXAMPLES/sbin/sysctl -a/sbin/sysctl -n kernel.hostname/sbin/sysctl -w kernel.domainname="example.com"/sbin/sysctl -p /etc/sysctl.confFILES/proc/sys /etc/sysctl.confSEE ALSOsysctl.conf(5)BUGSThe -A parameter behaves just as -a does.AUTHORGeorge Staikos, 21 Sep 1999                 SYSCTL(8) 

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