知识屋:更实用的电脑技术知识网站
所在位置:首页 > 操作系统 > linux

Linux fork死循环炸弹及其预防

发布时间:2014-09-05 17:18:56作者:知识屋

在Linux系统下执行这段代码 :(){ :|:& };: 就会引起死机,一旦执行起来后,唯一的方法就是重启系统。实际上这段代码是一段无限递归代码,将系统资源耗尽。

本文下面有这段代码的详细解释,为了防止fork炸弹,方法就是限制用户能够启动的进程数。具体做法,编辑/etc/security/limits.conf文件,在末尾加入 :

* hard nproc 200
将用户的进程数限制为200,经过测试,root账户不受这个限制。


Q. Can you explain following bash code or bash fork() bomb?
:(){ :|:& };:

A. This is a bash function. It gets called recursively (recursive function). This is most horrible code for any Unix / Linux box. It is often used by sys admin to test user processes limitations (Linux process limits can be configured via /etc/security/limits.conf and PAM).

Once a successful fork bomb has been activated in a system it may not be possible to resume normal operation without rebooting, as the only solution to a fork bomb is to destroy all instances of it.
WARNING! These examples may crash your computer if executed.
Understanding :(){ :|:& };: fork() bomb code

:() - It is a function name. It accepts no arguments at all. Generally, bash function is defined as follows:
foo(){
arg1=$1
echo
#do_something on $arg argument
}

fork() bomb is defined as follows:
:(){
:|:&
};:

:|: - Next it call itself using programming technique called recursion and pipes the output to another call of the function :. The worst part is function get called two times to bomb your system.

& - Puts the function call in the background so child cannot die at all and start eating system resources.

; - Terminate the function definition

: - Call (run) the function aka set the fork() bomb.

Here is more human readable code:
bomb() {
bomb | bomb &
}; bomb

Properly configured Linux / UNIX box should not go down when fork() bomb sets off.

 

(免责声明:文章内容如涉及作品内容、版权和其它问题,请及时与我们联系,我们将在第一时间删除内容,文章内容仅供参考)
收藏
  • 人气文章
  • 最新文章
  • 下载排行榜
  • 热门排行榜