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：


Shell代码  
1.sysctl [-n] [-e] -w variable=value   
2.sysctl [-n] [-e] -p  (default /etc/sysctl.conf)   
3.sysctl [-n] [-e] -a  
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




Shell代码  
1.**********************   
2.sysctl man page   
3.NAME   
4.sysctl - configure kernel parameters at runtime   
5.SYNOPSIS   
6.sysctl [-n] [-e] variable ...   
7.sysctl [-n] [-e] [-q] -w variable=value ...   
8.sysctl [-n] [-e] [-q] -p    
9.sysctl [-n] [-e] -a   
10.sysctl [-n] [-e] -A   
11.DESCRIPTION   
12.sysctl  is used to modify kernel parameters at runtime.    The parameters   
13.available are those listed under /proc/sys/.  Procfs  is     required  for   
14.sysctl(8)  support  in  Linux.    You can use sysctl(8) to both read and   
15.write sysctl data.   
16.PARAMETERS   
17.variable   
18.The name of a key to read from.  An  example  is    kernel.ostype.   
19.The ’/’ separator is also accepted in place of a ’.’.   
20.variable=value   
21.To set a key, use the form variable=value, where variable is the   
22.key and value is the value to set it to.    If the value  contains   
23.quotes or characters which are parsed by the shell, you may need   
24.to enclose the value in double quotes.   This  requires  the  -w   
25.parameter to use.   
26.-n     Use  this option to disable printing of the key name when print-   
27.ing values.   
28.-e     Use this option to ignore errors about unknown keys.   
29.-N     Use this option to only print the names. It may be  useful  with   
30.shells that have programmable completion.   
31.-q     Use this option to not display the values set to stdout.   
32.-w     Use this option when you want to change a sysctl setting.   
33.-p     Load   in      sysctl   settings   from   the   file     specified  or   
34./etc/sysctl.conf if none given.  Specifying - as filename     means   
35.reading data from standard input.   
36.-a     Display all values currently available.   
37.-A     Display all values currently available in table form.   
38.EXAMPLES   
39./sbin/sysctl -a   
40./sbin/sysctl -n kernel.hostname   
41./sbin/sysctl -w kernel.domainname="example.com"  
42./sbin/sysctl -p /etc/sysctl.conf   
43.FILES   
44./proc/sys /etc/sysctl.conf   
45.SEE ALSO   
46.sysctl.conf(5)   
47.BUGS   
48.The -A parameter behaves just as -a does.   
49.AUTHOR   
50.George Staikos,    
51.21 Sep 1999                 SYSCTL(8)