Loading... <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px"><strong>前言:</strong></span></span></p> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px"><strong> 作为一个合格的运维人员,系统的启动过程我们需要牢记在心,此文不深入探讨,只求大致理解CentOS6的启动过程。<br /></strong></span></span></p> <p><span style="font-size: 20px"><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai"><br /></span></strong></span></p> <p><span style="font-size: 20px"><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai"><br /></span></strong></span></p> <p><span style="font-size: 20px"><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai"><br /></span></strong></span></p> <p><span style="font-size: 20px"><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai">一张图带你了解CentOS6的启动过程</span></strong></span></p> <hr /> <p><img src="//cto.wang/usr/uploads/2016/07/20160703180756-37.png" title="1457914609577772.png" alt="blob.png" /></p> <p><strong>注意:图片放大查看效果更佳</strong></p> <p><strong><br /></strong></p> <p></p> <hr /> <p><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">上图各阶段详解</span></strong></p> <p><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></strong></p> <hr /> <p><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></strong></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">POST:计算机开机时BIOS对其各硬件的简单测试,测试各硬件的完整性</span></p> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px">BootSqunce:加电自检后根据用户自己这次开机手动设置的接口或者BIOS默认设置依次检查FirstBoot,SecondaryBoot…等定义的接口是否能引导系统启动</span></span></p> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px">MBR:Master Boot Record, 主引导记录,是硬盘的第一个扇区,MBR中包含了Bootloader,分区表等重要信息。</span></span></p> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px">Bootloader:引导程序,通过MBR中找到的Bootloader来引导系统,CentOS6中的Bootloader是Grub Legacy,其实这里的Bootloader只是整个Bootloader的Stage1,我们在后面进行说明</span></span></p> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px">Kernel–>intramfs:通过Bootloader选择内核,内核进行自解压后,解压initramfs加载额外驱动并将其以只读的方式挂载为根分区。</span></span></p> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px">/sbin/init:init程序是系统初始化程序,有着至关重要的作用,可以提供设置系统时间,检测挂载文件系统等作用,我们会在后面进行详细说明,系统初始化结束之后切换根分区</span></span></p> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px">mingetty–>login:mingetty负责启动虚拟终端,然后调用login程序供用户登录系统</span></span></p> <hr /> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px"><br /></span></span></p> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px"></span></span></p> <hr /> <p><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">CentOS6中的Bootloader</span></strong></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></p> <hr /> <p> <span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">CentOS6默认使用Grub Legacy为Bootloader,一张图带你简单了解Grub的启动过程</span><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"> </span><img src="//cto.wang/usr/uploads/2016/07/20160703180756-1.png" title="1457915978488640.png" alt="blob.png" style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px" /></p> <p></p> <p><strong>注意:图片放大查看效果更佳</strong></p> <p></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></p> <hr /> <p><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">上图各阶段详解</span></strong></p> <p><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></strong></p> <hr /> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">stage1:MBR分区中的Bootloader只有256字节,这显然并不能直接驱动我们的内核,其实MBR中的Bootloader只是Grub Legacy的stage1(第一阶段),可以引导到存在Grub Legacy分区</span></p> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px">stafe1_5:stage1<span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">并不知道Grub Legacy所在分区的驱动,所以在MBR后的扇区中有着一些常用的文件系统驱动可供stage1引导至stage2中</span></span></span></p> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px"><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">stage2:真正的Grub核心文件的存放位置,其中包含了Grub Legacy的配置文件,可通过stage2真正的加载内核</span></span></span></p> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px"><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></span></span></p> <hr /> <p><span style="font-family:楷体, 楷体_GB2312, SimKai"><span style="font-size: 20px"><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></span></span></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai"></span></p> <hr /> <p><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">CentOS6中的init程序</span></strong></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></p> <hr /> <p> <span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">其实在CentOS6中的init程序已经不是传统的SysVinit(sysV系UNIX的init),采用了upstart代替SysV,但是CentOS6为了简便管理员的操作,upstart的很多特性并没有凸显,例如:启动服务在原生upstart系统中应该是initctl start JOB,但是CentOS6中并不支持,因为在CentOS6中的服务启动脚本还是以原来SysV的形式提供的,所以我们采用SysV init的图来讲CentOS6的系统初始化过程。</span></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"><img src="//cto.wang/usr/uploads/2016/07/20160703180756-53.png" title="1457917617175729.png" alt="blob.png" /></span></p> <p><strong>注意:图片放大查看效果更佳</strong></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></p> <hr /> <p><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">上图各阶段详解</span></strong></p> <p><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></strong></p> <hr /> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">/sbin/init:内核自解压加载ramfs后启动init开始初始化系统</span></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">/etc/rc.d/rc:通过读取/etc/inittab和/etc/init.d/获取相应运行级别和配置</span></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">/etc/rc.d/rc.sysinit:通过初始化脚本,完成系统初始化,例如:设置系统时间、检测自动挂载文件系统、激活udev和SElinux….</span></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">/etc/rc.d/rc*.d/:在对应运行级别的目录下,启动S开头的程序,关闭K开头的程序</span></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">mingetty–>login:初始化完成后启动虚拟终端,然后调用Login程序供用户登录</span></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"><br /></span></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"><br /></span></p> <p><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"></span></p> <hr /> <p><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px">总结:</span><br /></strong></p> <p><strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"> 虽然写的不是特别详细,但是可以让大家大致了解CentOS6的启动过程,Grub legacy部分会抽空写一篇相应博文来详细叙述。</span></strong><span style="font-family: 楷体, 楷体_GB2312, SimKai;font-size: 20px"><br /></span></p> 最后修改:2021 年 12 月 10 日 10 : 53 AM © 允许规范转载 赞赏 如果觉得我的文章对你有用,请随意赞赏 赞赏作者 支付宝微信