Linux_11_系统启动和内核管理

1 C entOS 6 的启动管理

1.1 Linux 组成

• kernel 实现进程管理、内存管理、网络管理、驱动程序、文件系统、安全功能等功能

• rootfs 包括程序和 glibc 库

  ​ 程序:二进制执行文件

  ​ 库: 函数集合，function， 调用接口 (头文件负责描述)

1.2 内核设计流派

• 宏内核(monolithic kernel): 又称单内核和强内核，Unix，Linux

  ​ 把所有系统服务都放到内核里，所有功能集成于同一个程序，分层实现不同功能，系统庞大复杂Linux其实在单内核内核实现了模块化，也就相当于吸收了微内核的优点

• 微内核(micro kernel): Windows，Solaris，HarmonyOS

  ​ 简化内核功能，在内核之外的用户态尽可能多地实现系统服务，同时加入相互之间的安全保护，每种功能使用一个单独子系统实现，将内核功能移到用户空间，性能差

1.3 CentOS 6启动流程

1.3.1 CentOs 6 启动流程

1. 加载BIOS的硬件信息，获取第一个启动设备
2. 读取第一个启动设备MBR的引导加载程序(grub)的启动信息
3. 加载核心操作系统的核心信息，核心开始解压缩，并尝试驱动所有的硬件设备
4. 核心执行init程序，并获取默认的运行信息
5. init程序执行/etc/rc.d/rc.sysinit文件，重新挂载根文件系统
6. 启动核心的外挂模块
7. init执行运行的各个批处理文件(scripts)
8. init执行/etc/rc.d/rc.local
9. 执行/bin/login程序，等待用户登录
10. 登录之后开始以shell控制主机

1.3.1 硬件启动POST

POST：Power-On-Self-Test，加电自检，是BIOS功能的一个主要部分。负责完成对CPU、主板、内存、硬盘子系统、显示子系统、串并行接口、键盘等硬件情况的检测

主板的ROM：BIOS，Basic lnput and Output System 基本输入输出系统，保存着有关计算机系统最重要的基本输入输出程序，系统信息设置、开机加电自检程序和系统启动自举程序等

主板的RAM：CMOS 互补金属氧化物半导体，保存各项参数的设定，按次序查找引导设备，第一个有引导程序的设备为本次启动设备

1.3.2 bootloader 启动/引导加载器

1.3.2.1 grub 功能和组成

bootloader：引导加载器，引导程序

• windows：ntloader，仅是启动OS
• Linux：功能丰富，提供菜单，允许用户选择要启动系统或不同的内核版本，把用户选定的内核装载到内存中的特定空间中，解压、展开，并把系统控制权移交给内核

Linux的bootloader

• LILO：LInux LOader，早期的bootloader，功能单一，已淘汰
• GRUB：GRand Unified Bootloader，C5/6 使用GRUB 0.97: GRUB Legacy，C7 以后使用GRUB 2.02

GRUB 启动阶段

• primary boot loader：
  • 1st stage：MBR的前446个字节)
  • 1.5 stage：mbr 之后的扇区，让stage1中的bootloader能识别stage2所在的分区上的文件
• secondary boot loader：2nd stage，分区文件/boot/grub/

例：

[root@CentOS8 ~]#rpm -qa grub*
grub2-tools-minimal-2.02-106.el8.x86_64
grub2-common-2.02-106.el8.noarch
grub2-tools-2.02-106.el8.x86_64
grub2-pc-2.02-106.el8.x86_64
grub2-pc-modules-2.02-106.el8.noarch
grub2-tools-extra-2.02-106.el8.x86_64
grubby-8.40-42.el8.x86_64[root@CentOS8 ~]#rpm -qi grub2-pc
Name        : grub2-pc
Epoch       : 1
Version     : 2.02
Release     : 106.el8
Architecture: x86_64
Install Date: Tue 30 May 2023 11:33:23 PM CST
Group       : System Environment/Base
Size        : 0

1.3.2.2 CentOS 6 grub 安装

安装grub:

(1)grub-install 安装grub stage1和stage1_5到/dev/DISK磁盘上，并复制GRUB相关文件到 DIR/boot

目录下

grub-install --root-directory=DIR /dev/DISK

(2) grub

grub> root (hd#,#)@第#个硬盘第#个分区
grub> setup (hd#)

例1：破坏C6系统的启动文件的第一阶段的446字节，然后使用救援模式修复

[root@CentOS6 ~]#hexdump -C -n 512 /dev/sda
00000000  eb 48 90 10 8e d0 bc 00  b0 b8 00 00 8e d8 8e c0  |.H..............|
00000010  fb be 00 7c bf 00 06 b9  00 02 f3 a4 ea 21 06 00  |...|.........!..|
00000020  00 be be 07 38 04 75 0b  83 c6 10 81 fe fe 07 75  |....8.u........u|
00000030  f3 eb 16 b4 02 b0 01 bb  00 7c b2 80 8a 74 03 02  |.........|...t..|
00000040  80 00 00 80 a0 0c 05 00  00 08 fa 90 90 f6 c2 80  |................|
00000050  75 02 b2 80 ea 59 7c 00  00 31 c0 8e d8 8e d0 bc  |u....Y|..1......|
00000060  00 20 fb a0 40 7c 3c ff  74 02 88 c2 52 f6 c2 80  |. ..@|<.t...R...|
00000070  74 54 b4 41 bb aa 55 cd  13 5a 52 72 49 81 fb 55  |tT.A..U..ZRrI..U|
00000080  aa 75 43 a0 41 7c 84 c0  75 05 83 e1 01 74 37 66  |.uC.A|..u....t7f|
00000090  8b 4c 10 be 05 7c c6 44  ff 01 66 8b 1e 44 7c c7  |.L...|.D..f..D|.|
000000a0  04 10 00 c7 44 02 01 00  66 89 5c 08 c7 44 06 00  |....D...f.\..D..|
000000b0  70 66 31 c0 89 44 04 66  89 44 0c b4 42 cd 13 72  |pf1..D.f.D..B..r|
000000c0  05 bb 00 70 eb 7d b4 08  cd 13 73 0a f6 c2 80 0f  |...p.}....s.....|
000000d0  84 f0 00 e9 8d 00 be 05  7c c6 44 ff 00 66 31 c0  |........|.D..f1.|
000000e0  88 f0 40 66 89 44 04 31  d2 88 ca c1 e2 02 88 e8  |..@f.D.1........|
000000f0  88 f4 40 89 44 08 31 c0  88 d0 c0 e8 02 66 89 04  |..@.D.1......f..|
00000100  66 a1 44 7c 66 31 d2 66  f7 34 88 54 0a 66 31 d2  |f.D|f1.f.4.T.f1.|
00000110  66 f7 74 04 88 54 0b 89  44 0c 3b 44 08 7d 3c 8a  |f.t..T..D.;D.}<.|
00000120  54 0d c0 e2 06 8a 4c 0a  fe c1 08 d1 8a 6c 0c 5a  |T.....L......l.Z|
00000130  8a 74 0b bb 00 70 8e c3  31 db b8 01 02 cd 13 72  |.t...p..1......r|
00000140  2a 8c c3 8e 06 48 7c 60  1e b9 00 01 8e db 31 f6  |*....H|`......1.|
00000150  31 ff fc f3 a5 1f 61 ff  26 42 7c be 7f 7d e8 40  |1.....a.&B|..}.@|
00000160  00 eb 0e be 84 7d e8 38  00 eb 06 be 8e 7d e8 30  |.....}.8.....}.0|
00000170  00 be 93 7d e8 2a 00 eb  fe 47 52 55 42 20 00 47  |...}.*...GRUB .G|
00000180  65 6f 6d 00 48 61 72 64  20 44 69 73 6b 00 52 65  |eom.Hard Disk.Re|
00000190  61 64 00 20 45 72 72 6f  72 00 bb 01 00 b4 0e cd  |ad. Error.......|
000001a0  10 ac 3c 00 75 f4 c3 00  00 00 00 00 00 00 00 00  |..<.u...........|
000001b0  00 00 00 00 00 00 00 00  05 7f 0d 00 00 00 80 20  |............... |
000001c0  21 00 83 aa 28 82 00 08  00 00 00 00 20 00 00 aa  |!...(....... ...|
000001d0  29 82 83 fe ff ff 00 08  20 00 00 00 80 0c 00 fe  |)....... .......|
000001e0  ff ff 83 fe ff ff 00 08  a0 0c 00 80 1a 06 00 fe  |................|
000001f0  ff ff 05 fe ff ff 00 88  ba 12 00 78 45 06 55 aa  |...........xE.U.|
00000200
[root@CentOS6 ~]#dd if=/dev/zero of=/dev/sda bs=1 count=446		#将前446字节写为0
446+0 records in
446+0 records out
446 bytes (446 B) copied, 0.000366533 s, 1.2 MB/s
[root@CentOS6 ~]#hexdump -C -n 512 /dev/sda -v
00000000  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000020  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000030  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000040  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000060  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000070  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000080  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000090  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000000a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000000b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000000c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000000d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000000e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000000f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000100  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000110  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000120  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000130  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000140  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000150  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000160  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000170  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000180  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000190  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000001b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 80 20  |............... |
000001c0  21 00 83 aa 28 82 00 08  00 00 00 00 20 00 00 aa  |!...(....... ...|
000001d0  29 82 83 fe ff ff 00 08  20 00 00 00 80 0c 00 fe  |)....... .......|
000001e0  ff ff 83 fe ff ff 00 08  a0 0c 00 80 1a 06 00 fe  |................|
000001f0  ff ff 05 fe ff ff 00 88  ba 12 00 78 45 06 55 aa  |...........xE.U.|
00000200
[root@CentOS6 ~]#reboot

有光盘的情况下：

**无光盘的情况下：**先尝试网络启动，失败后提示没有操作系统

修复：

连接光盘，重启加载时按下ESC显示boot menu，选择光盘启动

选择救援模式

配置语言、键盘、网络等

回车启动一个shell

bash-4.1#df			#查看我们系统真正的硬盘被挂载到/mnt/sysimage
bash-4.1#chroot /mnt/sysimage/		#切换到系统的硬盘下
bash-4.1#grub-install /dev/sda		#修复sda
#提示成功
bash-4.1#sync		#将缓冲区内容写入到磁盘，防止直接重启而未写入磁盘

bash-4.1#hexdump -C -n 512 /dev/sda		#查看sda的前512字节内容，已经修复
bash-4.1#reboot		#重启

成功启动

例2：破坏C6系统的启动文件的第一阶段的446字节，然后使用grub修复

[root@CentOS6 ~]#dd if=/dev/zero of=/dev/sda bs=1 count=446		#将前446字节写为0
446+0 records in
446+0 records out
446 bytes (446 B) copied, 0.000366533 s, 1.2 MB/s[root@CentOS6 ~]#grub
Probing devices to guess BIOS drives. This may take a long time.GNU GRUB  version 0.97  (640K lower / 3072K upper memory)[ Minimal BASH-like line editing is supported.  For the first word, TABlists possible command completions.  Anywhere else TAB lists the possiblecompletions of a device/filename.]
grub> root (hd0,0)
root (hd0,0)Filesystem type is ext2fs, partition type 0x83
grub> setup (hd0)
setup (hd0)Checking if "/boot/grub/stage1" exists... noChecking if "/grub/stage1" exists... yesChecking if "/grub/stage2" exists... yesChecking if "/grub/e2fs_stage1_5" exists... yesRunning "embed /grub/e2fs_stage1_5 (hd0)"...  27 sectors are embedded.
succeededRunning "install /grub/stage1 (hd0) (hd0)1+27 p (hd0,0)/grub/stage2 /grub/grub.conf"... succeeded
Done.
[root@CentOS6 ~]#hexdump -C -n 512 /dev/sda
00000000  eb 48 90 00 00 00 00 00  00 00 00 00 00 00 00 00  |.H..............|
00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
*
00000030  00 00 00 00 00 00 00 00  00 00 00 00 00 00 03 02  |................|
00000040  ff 00 00 20 01 00 00 00  00 02 fa 90 90 f6 c2 80  |... ............|
00000050  75 02 b2 80 ea 59 7c 00  00 31 c0 8e d8 8e d0 bc  |u....Y|..1......|
00000060  00 20 fb a0 40 7c 3c ff  74 02 88 c2 52 f6 c2 80  |. ..@|<.t...R...|
00000070  74 54 b4 41 bb aa 55 cd  13 5a 52 72 49 81 fb 55  |tT.A..U..ZRrI..U|
00000080  aa 75 43 a0 41 7c 84 c0  75 05 83 e1 01 74 37 66  |.uC.A|..u....t7f|
00000090  8b 4c 10 be 05 7c c6 44  ff 01 66 8b 1e 44 7c c7  |.L...|.D..f..D|.|
000000a0  04 10 00 c7 44 02 01 00  66 89 5c 08 c7 44 06 00  |....D...f.\..D..|
000000b0  70 66 31 c0 89 44 04 66  89 44 0c b4 42 cd 13 72  |pf1..D.f.D..B..r|
000000c0  05 bb 00 70 eb 7d b4 08  cd 13 73 0a f6 c2 80 0f  |...p.}....s.....|
000000d0  84 f0 00 e9 8d 00 be 05  7c c6 44 ff 00 66 31 c0  |........|.D..f1.|
000000e0  88 f0 40 66 89 44 04 31  d2 88 ca c1 e2 02 88 e8  |..@f.D.1........|
000000f0  88 f4 40 89 44 08 31 c0  88 d0 c0 e8 02 66 89 04  |..@.D.1......f..|
00000100  66 a1 44 7c 66 31 d2 66  f7 34 88 54 0a 66 31 d2  |f.D|f1.f.4.T.f1.|
00000110  66 f7 74 04 88 54 0b 89  44 0c 3b 44 08 7d 3c 8a  |f.t..T..D.;D.}<.|
00000120  54 0d c0 e2 06 8a 4c 0a  fe c1 08 d1 8a 6c 0c 5a  |T.....L......l.Z|
00000130  8a 74 0b bb 00 70 8e c3  31 db b8 01 02 cd 13 72  |.t...p..1......r|
00000140  2a 8c c3 8e 06 48 7c 60  1e b9 00 01 8e db 31 f6  |*....H|`......1.|
00000150  31 ff fc f3 a5 1f 61 ff  26 42 7c be 7f 7d e8 40  |1.....a.&B|..}.@|
00000160  00 eb 0e be 84 7d e8 38  00 eb 06 be 8e 7d e8 30  |.....}.8.....}.0|
00000170  00 be 93 7d e8 2a 00 eb  fe 47 52 55 42 20 00 47  |...}.*...GRUB .G|
00000180  65 6f 6d 00 48 61 72 64  20 44 69 73 6b 00 52 65  |eom.Hard Disk.Re|
00000190  61 64 00 20 45 72 72 6f  72 00 bb 01 00 b4 0e cd  |ad. Error.......|
000001a0  10 ac 3c 00 75 f4 c3 00  00 00 00 00 00 00 00 00  |..<.u...........|
000001b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 80 20  |............... |
000001c0  21 00 83 aa 28 82 00 08  00 00 00 00 20 00 00 aa  |!...(....... ...|
000001d0  29 82 83 fe ff ff 00 08  20 00 00 00 80 0c 00 fe  |)....... .......|
000001e0  ff ff 83 fe ff ff 00 08  a0 0c 00 80 1a 06 00 fe  |................|
000001f0  ff ff 05 fe ff ff 00 88  ba 12 00 78 45 06 55 aa  |...........xE.U.|
00000200

例3：破坏1.5阶段的第2至第25个扇区，将内容置为0，然后修复

[root@CentOS6 ~]#dd if=/dev/zero of=/dev/sda bs=512 count=25 seek=1
25+0 records in
25+0 records out
12800 bytes (13 kB) copied, 0.00245147 s, 5.2 MB/s[root@CentOS6 ~]#hexdump -C -n 5120 /dev/sda -v
00000000  eb 48 90 00 00 00 00 00  00 00 00 00 00 00 00 00  |.H..............|
00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000020  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000030  00 00 00 00 00 00 00 00  00 00 00 00 00 00 03 02  |................|
00000040  ff 00 00 20 01 00 00 00  00 02 fa 90 90 f6 c2 80  |... ............|
00000050  75 02 b2 80 ea 59 7c 00  00 31 c0 8e d8 8e d0 bc  |u....Y|..1......|
00000060  00 20 fb a0 40 7c 3c ff  74 02 88 c2 52 f6 c2 80  |. ..@|<.t...R...|
00000070  74 54 b4 41 bb aa 55 cd  13 5a 52 72 49 81 fb 55  |tT.A..U..ZRrI..U|
00000080  aa 75 43 a0 41 7c 84 c0  75 05 83 e1 01 74 37 66  |.uC.A|..u....t7f|
00000090  8b 4c 10 be 05 7c c6 44  ff 01 66 8b 1e 44 7c c7  |.L...|.D..f..D|.|
000000a0  04 10 00 c7 44 02 01 00  66 89 5c 08 c7 44 06 00  |....D...f.\..D..|
000000b0  70 66 31 c0 89 44 04 66  89 44 0c b4 42 cd 13 72  |pf1..D.f.D..B..r|
000000c0  05 bb 00 70 eb 7d b4 08  cd 13 73 0a f6 c2 80 0f  |...p.}....s.....|
000000d0  84 f0 00 e9 8d 00 be 05  7c c6 44 ff 00 66 31 c0  |........|.D..f1.|
000000e0  88 f0 40 66 89 44 04 31  d2 88 ca c1 e2 02 88 e8  |..@f.D.1........|
000000f0  88 f4 40 89 44 08 31 c0  88 d0 c0 e8 02 66 89 04  |..@.D.1......f..|
00000100  66 a1 44 7c 66 31 d2 66  f7 34 88 54 0a 66 31 d2  |f.D|f1.f.4.T.f1.|
00000110  66 f7 74 04 88 54 0b 89  44 0c 3b 44 08 7d 3c 8a  |f.t..T..D.;D.}<.|
00000120  54 0d c0 e2 06 8a 4c 0a  fe c1 08 d1 8a 6c 0c 5a  |T.....L......l.Z|
00000130  8a 74 0b bb 00 70 8e c3  31 db b8 01 02 cd 13 72  |.t...p..1......r|
00000140  2a 8c c3 8e 06 48 7c 60  1e b9 00 01 8e db 31 f6  |*....H|`......1.|
00000150  31 ff fc f3 a5 1f 61 ff  26 42 7c be 7f 7d e8 40  |1.....a.&B|..}.@|
00000160  00 eb 0e be 84 7d e8 38  00 eb 06 be 8e 7d e8 30  |.....}.8.....}.0|
00000170  00 be 93 7d e8 2a 00 eb  fe 47 52 55 42 20 00 47  |...}.*...GRUB .G|
00000180  65 6f 6d 00 48 61 72 64  20 44 69 73 6b 00 52 65  |eom.Hard Disk.Re|
00000190  61 64 00 20 45 72 72 6f  72 00 bb 01 00 b4 0e cd  |ad. Error.......|
000001a0  10 ac 3c 00 75 f4 c3 00  00 00 00 00 00 00 00 00  |..<.u...........|
000001b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 80 20  |............... |
000001c0  21 00 83 aa 28 82 00 08  00 00 00 00 20 00 00 aa  |!...(....... ...|
000001d0  29 82 83 fe ff ff 00 08  20 00 00 00 80 0c 00 fe  |)....... .......|
000001e0  ff ff 83 fe ff ff 00 08  a0 0c 00 80 1a 06 00 fe  |................|
000001f0  ff ff 05 fe ff ff 00 88  ba 12 00 78 45 06 55 aa  |...........xE.U.|
00000200  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000210  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000220  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000230  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000240  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000250  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000260  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000270  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000280  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000290  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000002a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000002b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000002c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000002d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000002e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000002f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000300  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000310  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000320  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000330  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000340  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000350  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000360  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000370  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000380  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000390  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000003a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000003b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000003c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000003d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000003e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000003f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000400  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000410  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000420  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000430  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000440  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000450  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000460  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000470  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000480  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000490  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000004a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000004b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000004c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000004d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000004e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000004f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000500  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000510  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000520  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000530  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000540  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000550  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000560  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000570  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000580  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000590  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000005a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000005b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000005c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000005d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000005e0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000005f0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000600  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000610  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000620  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000630  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000640  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000650  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000660  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000670  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000680  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
00000690  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000006a0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000006b0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000006c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
000006d0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
[root@CentOS6 ~]#reboot

重启后系统无法打开，但错误提示不同：

此时1阶段正常，系统认为硬盘可以启动，所以一直在加载，而不去寻找光盘等设备来启动，就会卡在这里

**修复：**同样的，进入救援模式，然后切换根，然后grub-install /dev/sda即可

1.3.2.3 grub legacy 管理

配置文件： /boot/grub/grub.conf <-- /etc/grub.conf

stage2及内核等通常放置于一个基本磁盘分区

grub legacy 功用：

1. 提供启动菜单、并提供交互式接口
   • a：内核参数
   • e：编辑模式，用于编辑菜单
   • c：命令模式，交互式接口
2. 加载用户选择的内核或操作系统
   • 允许传递参数给内核
   • 可隐藏启动菜单
3. 为菜单提供了保护机制
   • 为编辑启动菜单进行认证
   • 为启用内核或操作系统进行认证

grub的命令行接口

help： 获取帮助列表
help KEYWORD： 详细帮助信息
find (hd#,#)/PATH/TO/SOMEFILE:
root (hd#,#)
kernel /PATH/TO/KERNEL_FILE： 设定本次启动的内核文件，额外还可添加许多内核支持使用的cmdline参数
例如： max_loop=100 selinux=0 init=/path/to/initinitrd /PATH/TO/INITRAMFS_FILE： 设定为选定的内核提供额外文件的ramdisk
boot： 引导启动选定的内核

cat /proc/cmdline 内核参数

内核参数文档：

/usr/share/doc/kernel-doc-2.6.32/Documentation/kernel-parameters.txt

grub legacy识别硬盘设备

(hd#,#)
hd#	磁盘编号，用数字表示;从0开始编号
#		分区编号，用数字表示，从0开始编号示例：
(hd0,0) 第一块硬盘，第一个分区

手动在grub命令行接口启动系统

grub> root (hd#,#)
grub> kernel /vmlinuz-VERSION-RELEASE ro root=/dev/DEVICE
grub> initrd /initramfs-VERSION-RELEASE.img
grub> boot

grub legacy配置文件： /boot/grub/grub.conf

default=#：	设定默认启动的菜单项;落单项(title)编号从0开始
timeout=#：	指定菜单项等待选项选择的时长
splashimage=(hd#,#)/PATH/XPM_FILE：	菜单背景图片文件路径
password [--md5 | encrypt] STRING：	启动菜单编辑认证
hiddenmenu：	隐藏菜单
title TITLE：	定义菜单项“标题”，可出现多次	
root (hd#,#)：	查找stage2及kernel文件所在设备分区;为grub的根
kernel /PATH/TO/VMLINUZ_FILE [PARAMETERS]：	启动的内核
initrd /PATH/TO/INITRAMFS_FILE：	内核匹配的ramfs文件
password [--md5|--encrypted ] STRING：	启动选定的内核或操作系统时进行认证

grub加密生成grub口令

grub-md5-crypt
grub-crypt

破解root口令：

(1)编辑grub菜单(选定要编辑的title，而后使用a 或 e 命令)
(2)在选定的kernel后附加1，s，S，single 都可以进入单用户模式
(3)在kernel所在行，键入“b”命令

范例： 给grub 添加密码，防止破解root密码

[root@centos6 ~]#grub-crypt
Password:
Retype password:
S6SRedtvBe0DOsM8yKqSykwmmnHsDb9WDRUuZbC3H1ZNwITf/Mh88MXa3JzXToxyyohXIXFWLIOMdgmYFfkwxxkP.VW3ypITa4P5zUKuT.[root@centos6 ~]#vim /boot/grub/grub.conf
default=0
timeout=5
password --encrypt	#加上这一行
56SRedtvBe0DOsM8ykqSykwmmnHSDb9WDRUuZbC3H1ZNwI1f/Mh88MXa3JzX1oxyyohXIXFWLIOMdgmYFfkwxxkP.VW3ypI1a4P5zUKuT.
splashimage=(hd0,0)/grub /splash.xpm.gz
hiddenmenu
title Centos 6 (2.6.32-754.e16.x86_64)#然后在系统选择时输入口令才能进入编辑
#不过进入救援模式，仍然可以跳过这些安全步骤，并修改密码

1.3.3 加载 kernel

kernel自身初始化过程：

1. 探测可识别到的所有硬件设备
2. 加载硬件动程序 (借助于ramdisk加载动)
3. 以只读方式挂载根文件系统
4. 运行用户空间的第一个应用程序：/sbin/init

Linux内核特点：

• 支持模块化：.ko (内核对象)，如： 文件系统，硬件驱动，网络协议等
• 支持内核模块的动态装载和卸载

内核组成部分：

• 核心文件： /boot/vmlinuz-VERSION-release

  ​ ramdisk：辅助的伪根系统，加载相应的硬件驱动，ramdisk --> ramfs 提高速度

  ​ C 5 /boot/initrd-VERSION-release.img

  ​ C 6以后版本 /boot/initramfs-VERSION-release.img

• 模块文件： /ib/modules/VERSION-release

ramdisk文件的制作：

mkinitrd命令

mkinitrd /boot/initramfs-$(uname -r).img $(uname -r)

dracut命令

dracut /boot/initramfs-$(uname -r).img $(uname -r)

例：误删除/boot/initramfs-2.6.32-754.el6.x86_64.img文件，导致系统无法启动，修复

[root@CentOS6 boot]#rm -f initrd-2.6.32-754.el6.x86_64kdump.img
[root@CentOS6 boot]#reboot
#进入救援模式
#chroot /mnt/sysimage	#切根
#mkinitrd /boot/initramfs-`uname -r`.img `uname -r`
#sync	
#reboot

例：误删除/boot/vmlinuz-2.6.32-754.el6.x86_64文件，即内核文件，导致系统无法启动，修复

[root@CentOS6 boot]#rm -f /boot/vmlinuz-2.6.32-754.el6.x86_64
#方式1
[root@CentOS6 boot]#reboot
#进入救援模式
#chroot /mnt/sysimage	#切根
#mount /dev/sr0 /mnt/	#挂载光盘
#cp /mnt/isolinux/vmlinuz 	/boot/vmlinuz-2.6.32-754.el6.x86_64
#sync
#reboot#方式2
#由于vmlinuz文件来源于光盘里的kernel包，直接重装即可
[root@CentOS6 boot]#rpm -qf vmlinuz-2.6.32-754.el6.x86_64
kernel-2.6.32-754.el6.x86_64

例：误删除/boot/*，grub和内核都被删除，进行故障恢复

#先修复内核，再修复Grub

范例：生成背景图片

[root@centos6 ~]#convert -resize 640x480 -colors 14 winner.png splash.xpm
[root@centos6 ~]#more splash.xpm
#生成splash.xpm.gz
[rootacentos6 ~]#qzip  splash.xpm
[root@centos6 ~]#mv splash.xpm.gz /boot/grub

1.3.4 init 初始化

使POST --> BootSeguence (BIOS) -->Bootloader(MBR) --> kernel(ramdisk) --> rootfs(只读) -->init(systemd)

init程序的类型：

• SysV： init，C5之前

  ​ 配置文件：/etc/inittab

• Upstart： init，C 6

  ​ 配置文件：/etc/inittab，/etc/init/*.conf

• Systemd：systemd，C 7

  ​ 配置文件： /usr/lib/systemd/system；/etc/systemd/system

1.3.4.1 运行级别

运行级别： 为系统运行或维护等目的而设定，0-6：7个级别，一般使用3，5做为默认级别

0：关机
1：单用户模式(root自动登录)，single，维护模式
2：多用户模式，启动网络功能，但不会启动NFS： 维护模式
3：多用户模式，正常模式：文本界面
4：预留级：可同3级别
5：多用户模式，正常模式：图形界面
6：重启

切换级别：

init #

查看级别：

runlevel
who -r

定义运行级别

/etc/inittab

C 5的inittab文件还定义以下内容

初始运行级别(RUN LEVEL)
系统初始化脚本
对应运行级别的脚本目录
捕获某个关键字顺序
定义UPS电源终端/恢复脚本
在虚拟控制台生成getty
在运行级别5初始化X

C 5的inittab文件每一行格式

id:runlevel:action:processid：是惟一标识该项的字符序列
runlevels： 定义了操作所使用的运行级别
action：指定了要执行的特定操作wait： 切换至此级别运行一次respawn： 此process终止，就重新启动之initdefault：设定默认运行级别;process省略sysinit：设定系统初始化方式
process：定义了要执行的进程

例：CentOS 6 /etc/inittab和相关文件

C6 init程序为 upstart， 其配置文件/etc/inittab，/etc/init/*.conf，配置文件的语法 遵循 upstart配置文件语法格式，和C 5不同

[root@CentOS6 ~]#cat /etc/inittab
# inittab is only used by upstart for the default runlevel.
#
# ADDING OTHER CONFIGURATION HERE WILL HAVE NO EFFECT ON YOUR SYSTEM.
#
# System initialization is started by /etc/init/rcS.conf
#
# Individual runlevels are started by /etc/init/rc.conf
#
# Ctrl-Alt-Delete is handled by /etc/init/control-alt-delete.conf
#
# Terminal gettys are handled by /etc/init/tty.conf and /etc/init/serial.conf,
# with configuration in /etc/sysconfig/init.
#
# For information on how to write upstart event handlers, or how
# upstart works, see init(5), init(8), and initctl(8).
#
# Default runlevel. The runlevels used are:
#   0 - halt (Do NOT set initdefault to this)
#   1 - Single user mode
#   2 - Multiuser, without NFS (The same as 3, if you do not have networking)
#   3 - Full multiuser mode
#   4 - unused
#   5 - X11
#   6 - reboot (Do NOT set initdefault to this)
#
id:3:initdefault:

例：control -alt-delete键默认行为是重启，工作中可以将其注释以防止误触

[root@CentOS6 init]#cat /etc/init/control-alt-delete.conf
# control-alt-delete - emergency keypress handling
#
# This task is run whenever the Control-Alt-Delete key combination is
# pressed.  Usually used to shut down the machine.
#
# Do not edit this file directly. If you want to change the behaviour,
# please create a file control-alt-delete.override and put your changes there.start on control-alt-deleteexec /sbin/shutdown -r now "Control-Alt-Delete pressed"

例：ntsysv图形界面修改服务，空格开启或关闭

例：一次性修改atd的7种模式

[root@CentOS6 init]#chkconfig --list atd
atd             0:off   1:off   2:off   3:on    4:on    5:on    6:off
[root@CentOS6 init]#chkconfig --level 34 atd off
[root@CentOS6 init]#chkconfig --list atd
atd             0:off   1:off   2:off   3:off   4:off   5:on    6:off
[root@CentOS6 init]#chkconfig atd on
[root@CentOS6 init]#chkconfig --list atd
atd             0:off   1:off   2:on    3:on    4:on    5:on    6:off

例：设置服务开机不启动

[root@CentOS6 init]#service iptables stop		#关闭服务
[root@CentOS6 init]#chkconfig iptables off	#设置开机不启动，开机启动则on

1.3.4.2 初始化脚本 sysinit

在所有服务加载之前执行初始化的脚本

/etc/rc.d/rc.sysinit

#由 rcS.conf文件调用
[root@CentOS6 init]#cat /etc/init/rcS.conf	
exec /etc/rc.d/rc.sysinit

系统初始化脚本功能

1. 设置主机名
2. 设置欢迎信息
3. 激活udev和selinux
4. 挂载/etc/fstab文件中定义的文件系统
5. 检测根文件系统，并以读写方式重新挂载根文件系统
6. 设置系统时钟
7. 激活swap设备
8. 根据/etc/sysctl.conf文件设置内核参数
9. 激活lvm及software raid设备
10. 加载额外设备的驱动程序
11. 清理操作

1.3.4.3 服务管理

service 命令:手动管理服务

service 服务 start|stop|restart
service --status-all

由rc.conf文件调用rc.d，rc调用服务脚本

[root@CentOS6 init]#cat /etc/init/rc.conf
exec /etc/rc.d/rc $RUNLEVEL

/etc/rc.d/rc 控制服务脚本的开机自动运行

for srv in /etc/rc.d/rcN.d/k*; do$srv stop
donefor srv in /etc/rc.d/rcN.d/s*; do$srv start
done

说明: rc N --> 意味着读取/etc/rc.d/rcN.d/

• K: K##: ##运行次序，数字越小，越先运行，数字越小的服务，通常为依赖到别的服务
• s: S##: ##运行次序，数字越小，越先运行，数字越小的服务，通常为被依赖到的服务

配置服务开机启动

• chkconfig命令
• ntsysv命令

chkconfig 命令管理服务

#查看服务在所有级别的启动或关闭设定情形:
chkconfig [--list] [name]#添加服务
Sysv的服务脚本放置于/etc/rc.d/init.d (/etc/init.d)
#!/bin/bash
chkconfig: LLLL nn nn	#LLLL 表示初始在哪个级别下启动，-表示都不启动
description :描述信息chkconfig --add name#删除服务
chkconfig --del name#修改指定的运行级别
chkconfig [--level levels] name <onlofflreset>
说明: --level LLLL:	指定要设置的级别;省略时表示2345

1.3.4.4 非独立服务

服务分为独立服务和非独立服务

瞬态 (Transient) 服务被超级守护进程 xinetd 进程所管理，也称为非独立服务，即用户不访问/使用该服务时，服务关闭，被xinetd进程所监控，当有用户访问某非独立服务时，则唤醒该非独立服务，使用结束则关闭服务

进入的请求首先被xinetd代理

配置文件:

etc/xinetd.conf
/etc/xinetd.d/<service>

用chkconfig控制非独立服务开机启动

示例: chkconfig tftp on

1.3.4.5 开机启动文件 rc.local

/etc/rc.d/rc.local

注意: 正常级别下，最后启动一个服务S99local没有链接至/etc/rc.d/init.d一个服务脚本，而是指向了/etc/rc.d/rc.local脚本

不便或不需写为服务脚本放置于/etc/rc.d/init.d/目录，且又想开机时自动运行的命令，可直接放警于/etc/rc.d/rc.local文件中
/etc/rc.d/rc.local在指定运行级别脚本后运行

1.3.5 Centos 启动过程总结

/sbin/init --> (/etc/inittab) --> 设置默认运行级别 --> 运行系统初始脚本/etc/rc.d/rc.sysinit、完成系统初始化 -->(关闭对应下需要关闭的服务)启动需要启动服务/etc/rc#.d/Sxxx，/etc/rc.d/rc.local --> 设置登录终端

参看: http://s4.51cto.com/wyfs02/M02/87/20/wKiom1fVBELjXsvaAAUkuL83t2Q304.jpg

1.4 自制linux系统

1.4.0为当前Linux系统增加硬盘

在现有Linux系统上构建系统，所以先在其上面加一块硬盘，上面存放文件系统与数据

在VMware上增加硬盘

默认当前无法找到硬盘

使用命令扫描一下磁盘

[root@CentOS6 ~]#lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sr0     11:0    1  3.7G  0 rom
sda      8:0    0  200G  0 disk
├─sda1   8:1    0    1G  0 part /boot
├─sda2   8:2    0  100G  0 part /
├─sda3   8:3    0 48.8G  0 part /data
├─sda4   8:4    0    1K  0 part
└─sda5   8:5    0    4G  0 part [SWAP]
[root@CentOS6 ~]#echo '- - -' > /sys/class/scsi_host/host0/scan
[root@CentOS6 ~]#echo '- - -' > /sys/class/scsi_host/host1/scan
[root@CentOS6 ~]#echo '- - -' > /sys/class/scsi_host/host2/scan
[root@CentOS6 ~]#lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sr0     11:0    1  3.7G  0 rom
sda      8:0    0  200G  0 disk
├─sda1   8:1    0    1G  0 part /boot
├─sda2   8:2    0  100G  0 part /
├─sda3   8:3    0 48.8G  0 part /data
├─sda4   8:4    0    1K  0 part
└─sda5   8:5    0    4G  0 part [SWAP]
sdb      8:16   0   20G  0 disk

1.4.1 分区并创建文件系统

fdisk /dev/sdb#分两个必要的分区：
[root@centos6 ~]#echo -e 'n\np\n1\n\n+1G\nw\n' fdisk /dev/sdb	#\n表示回车，给第一个分区分1G空间
[root@centos6 ~]#echo -e 'n\np\n2\n\n\n\nw\n' fdisk /dev/sdb		#将剩下空间给第二个分区
/dev/sdb1对应/boot /dev/sdb2对应根/[root@centos6 ~]#mkfs.ext4 /dev/sdb1
[root@centos6 ~]#mkfs.ext4 /dev/sdb2

例：

#1手动添加
[root@CentOS6 ~]#fdisk /dev/sdb
Device contains neither a valid DOS partition table, nor Sun, SGI or OSF disklabel
Building a new DOS disklabel with disk identifier 0x85b35a65.
Changes will remain in memory only, until you decide to write them.
After that, of course, the previous content won't be recoverable.Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)WARNING: DOS-compatible mode is deprecated. It's strongly recommended toswitch off the mode (command 'c') and change display units tosectors (command 'u').Command (m for help):
Command (m for help): n
Command actione   extendedp   primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-2610, default 1):
Using default value 1
Last cylinder, +cylinders or +size{K,M,G} (1-2610, default 2610): +1GCommand (m for help): w
The partition table has been altered!Calling ioctl() to re-read partition table.
Syncing disks.
#2非交互式直接添加
[root@CentOS6 ~]#echo -e 'n\np\n2\n\n\n\nw\n' | fdisk /dev/sdbWARNING: DOS-compatible mode is deprecated. It's strongly recommended toswitch off the mode (command 'c') and change display units tosectors (command 'u').Command (m for help): Command actione   extendedp   primary partition (1-4)
Partition number (1-4): First cylinder (133-2610, default 133): Using default value 133
Last cylinder, +cylinders or +size{K,M,G} (133-2610, default 2610): Using default value 2610Command (m for help): Command (m for help): The partition table has been altered!Calling ioctl() to re-read partition table.
Syncing disks.
[root@CentOS6 ~]#lsblk
NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sr0     11:0    1  3.7G  0 rom
sda      8:0    0  200G  0 disk
├─sda1   8:1    0    1G  0 part /boot
├─sda2   8:2    0  100G  0 part /
├─sda3   8:3    0 48.8G  0 part /data
├─sda4   8:4    0    1K  0 part
└─sda5   8:5    0    4G  0 part [SWAP]
sdb      8:16   0   20G  0 disk
├─sdb1   8:17   0    1G  0 part
└─sdb2   8:18   0   19G  0 part#格式化
[root@CentOS6 ~]#mkfs.ext4 /dev/sdb1
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
66384 inodes, 265064 blocks
13253 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=272629760
9 block groups
32768 blocks per group, 32768 fragments per group
7376 inodes per group
Superblock backups stored on blocks:32768, 98304, 163840, 229376Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: doneThis filesystem will be automatically checked every 34 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
[root@CentOS6 ~]#mkfs.ext4 /dev/sdb2
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=4096 (log=2)
Fragment size=4096 (log=2)
Stride=0 blocks, Stripe width=0 blocks
1245184 inodes, 4976133 blocks
248806 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=4294967296
152 block groups
32768 blocks per group, 32768 fragments per group
8192 inodes per group
Superblock backups stored on blocks:32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,4096000Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: doneThis filesystem will be automatically checked every 22 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.

1.4.2 挂载boot

[root@centos6 ~]#mkdir /mnt/boot 		#子目录必须为boot
[root@centos6 ~]#mount /dev/sdb1 /mnt/boot/

1.4.3 安装grub

[root@centos6 ~]#grub-install --root-directory=/mnt /dev/sdb

例：

[root@CentOS6 ~]#mkdir /mnt/boot
[root@CentOS6 ~]#mount /dev/sdb1 /mnt/boot/
[root@CentOS6 ~]#grub-install --root-directory=/mnt /dev/sdb
Probing devices to guess BIOS drives. This may take a long time.
Installation finished. No error reported.
This is the contents of the device map /mnt/boot/grub/device.map.
Check if this is correct or not. If any of the lines is incorrect,
fix it and re-run the script `grub-install'.(fd0)   /dev/fd0
(hd0)   /dev/sda
(hd1)   /dev/sdb
[root@CentOS6 ~]#ls /mnt/boot
grub  lost+found
[root@CentOS6 ~]#ls /mnt/boot/grub
device.map     fat_stage1_5  iso9660_stage1_5  minix_stage1_5     stage1  ufs2_stage1_5    xfs_stage1_5
e2fs_stage1_5  ffs_stage1_5  jfs_stage1_5      reiserfs_stage1_5  stage2  vstafs_stage1_5

1.4.4 准备内核和initramfs文件

[root@CentOS6 ~]#cp /boot/vmlinuz-2.6.32-754.el6.x86_64 /mnt/boot/vmlinuz
[root@CentOS6 ~]#cp /boot/initramfs-2.6.32-754.el6.x86_64.img /mnt/boot/initramfs

1.4.5 手动建立grub.conf

[root@CentOS6 ~]#cat /mnt/boot/grub/grub.conf
default=0
timeout=5
title joyce linux
root (hd0,0)
kernel /vmlinuz root=/dev/sda2 selinux=0  init=/bin/bash
initrd /initramfs

[root@CentOS6 ~]#tree /mnt/boot
/mnt/boot
├── grub
│   ├── device.map
│   ├── e2fs_stage1_5
│   ├── fat_stage1_5
│   ├── ffs_stage1_5
│   ├── grub.conf
│   ├── iso9660_stage1_5
│   ├── jfs_stage1_5
│   ├── minix_stage1_5
│   ├── reiserfs_stage1_5
│   ├── stage1
│   ├── stage2
│   ├── ufs2_stage1_5
│   ├── vstafs_stage1_5
│   └── xfs_stage1_5
├── initramfs
├── lost+found
└── vmlinuz

1.4.6 准备根下面相关程序和库

mkdir /mnt/sysroot
mount /dev/sdb2 /mnt/sysroot
mkdir -pv /mnt/sysroot/{etc,lib,lib64,bin,sbin,tmp,var,usr,sys,proc,opt,home,root,boot,dev,mnt,media}
复制bash等命令和相关库文件，如: bash,ifconfig,insmod,ping,mount,ls,cat,df,lsblk,blkid,fdisk,tree,ip,ps等#查询网卡驱动并拷贝
[root@CentOS6 ~]#ethtool -i eth0
driver: e1000
version: 7.3.21-k8-NAPI
firmware-version:
bus-info: 0000:02:01.0
supports-stalistics: yes
supports-test: yes
supports-eeprom-access: yes
supports-register-dump: yes
supports-priv-flags: no
[root@CentOS6 ~]#modinfo -n e1000
/lib/modules/2.6.32-754.el6.x86_64/kernel/drivers/net/e1000/e1000.ko
[root@CentOS6 ~]#cp /lib/modules/2.6.32-754.el6.x86_64/kernel/drivers/net/e1000/e1000.ko /mnt/sysroot/lib/		#将网卡驱动放在/mnt/sysroot/lib下[root@centos6 ~]#chroot /mnt/sysroot

1.4.7 准备新的虚拟机

将当前C6机器关机，将刚创建的硬盘拷贝到test文件夹中

创建一个新的Linux6虚拟机，将前一虚拟机sdb硬盘对应的vmdk文件增加进去，删除原有磁盘

开机

1.5 启动过程的故障排错

1.5.1 实战案例

故障：删除 /sbin/init 无法启动

恢复过程

先进入grub菜单，在kernel参数后加 selinux=0 init=/bin/bash
mount -o remount,rw /
mount /dev/sr0 /mnt/
rpm2cpio /mnt/Packages/upstart.xxx.rpm cpio -idv ./sbin/init
mv ./sbin/init /sbin/

1.5.2 实战案例

故障：rm -rf /boot/* 和 /etc/fstab 进行恢复

恢复过程

1.用光盘进入 rescue mode，找到/ 所在分区并恢复/etc/fstab

进入救援模式，由于没有分区表，因此无法挂载操作系统的根

fdisk -l
mkdir /mnt/rootdir
mount /dev/sdaN /mnt/rootdir
ls /mnt/rootdir
mount /dev/sda2 /mnt/rootdirvim /mnt/rootdir/etc/fstab
/dev/sda1 /boot ext4 defaults 0 0
/dev/sda2 /			ext4 defaults 0 0
/dev/sda3 /data ext4 defaults 0 0
/dev/sda5 swap 	swap defaults 0 0
reboot

2.rescue mode 恢复内核和initrd 文件

/dev/sda2 --> /mnt/sysimagechroot /mnt/sysimage
mount /dev/srO /mnt/
#方法1
rpm -ivh /mnt/Packages/kernel.xxxx.rpm --force#方法2
cp /mnt/isolinux/vmlinuz /boot/
mkinitrd /boot/initramfs.img `uname -r`

3.修复grub

grub-install /dev/sda
vim /boot/grub/grub.conf 方法2
[root@centos6 ~]#cat /boot/grub/grub.conf
default=0
timeout=5
title centos
kernel /vmlinuz root=/dev/sda2
initrd /initramfs.img

4.reboot

2 /proc 目录和内核参数管理

/proc目录: 内核把自己内部状态信息及统计信息，以及可配置参数通过proc伪文件系统加以输出帮助: man proc
内核参数：

• 只读:只用于输出信息
• 可写: 可接受用户指定“新值”来实现对内核某功能或特性的配置

/proc/sys 设置：

sysctl命令用于查看或设定此目录中诸多参数

sysctl -w path.to.parameter=VALUE例：
[root@CentOS6 ~]#cat /proc/sys/net/ipv4/ip_forward
0
[root@CentOS6 ~]#echo 1 >/proc/sys/net/ipv4/ip_forward
#等价于：
[root@CentOS6 ~]#sysctl -w net.ipv4.ip_forward=1

不过这是临时修改，无法持久保存

默认配置文件：/etc/sysct.conf （总文件）及以下文件

/run/sysctl.d/*.conf
/etc/sysctl.d/*.conf
/usr/local/lib/sysctl.d/* .conf
/usr/lib/sysctl.d/*.conf
lib/sysctl.d/* .conf
etc/sysctl.conf

最好是分类，单独放一个，或者放总文件里

范例:修改主机名

sysctl -w kernel.hostname=mail.joyce.com

echo命令通过重定向方式也可以修改大多数参数的值

echo "VALUE”> /proc/sys/path/to/parameter

范例:

echo “websrv” > /proc/sys/kernel/hostname

sysctl命令

1. 临时设置某参数

   sysctl -w parameter=VALUE
   

2. 通过读取配置文件设置参数

   sysctl -p [/path/to/conf_filel
   

3. 查看所有生效参数

   sysctl -a
   

常用的内核参数

net.ipv4.ip_forward
net.ipv4.icmp_echo_ignore_all	#设置1则其他主机无法ping通本主机
net.ipv4.ip_nonocal_bind		#允许应用程序可以监听本地不存在的IP
vm.drop_caches			#可以释放缓冲区
fs.file-max = 1020000	#最多可以打开的文件数，打开一个文件分配一个文件描述符

例：

[root@centos8 ~]#cat /proc/sys/net/ipv4/icmp_echo_ignore_all
0
[root@centos8 ~]#vim /etc/sysctl.d/test.conf
[root@centos8 ~]#cat /etc/sysctl.d/test.conf
net.ipv4.icmp_echo_ignore_all=1
[root@centos8 ~]#sysctl -p /etc/sysctl.d/test.conf
net.ipv4.icmp_echo_ignore_all =1
[root@centos8 ~]#cat /proc/sys/net/ipv4/icmp_echo_ignore_all
1

3 /sys 目录

/sys目录:
使用sysfs文件系统，为用户使用的伪文件系统，输出内核识别出的各硬件设备的相关属性信息，也有内核对硬件特性的设定信息，有些参数是可以修改的，用于调整硬件工作特性

udev通过此路径下输出的信息动态为各设备创建所需要设备文件，udev是运行用户空间程序专用工具: udevadmin，hotplug

udev为设备创建设备文件时，会读取其事先定义好的规则文件，一般在/etc/udev/rules.d及/usr/lib/udev/rules.d目录下

4 内核模块管理和编译

单内核体系设计、但充分借鉴了微内核设计体系的优点，为内核引入模块化机制

内核组成部分:、

• kernel: 内核核心，一般为bzlmage，通常在/boot目录下，名称为 vmlinuz-VERSION-RELEASE
• kernel object: 内核对象，一般放置于/lib/modules/VERSION-RELEASE/
• 辅助文件: ramdisk、initrd（C5及以前，模拟磁盘，进入后还要进入文件系统）、initramfs（C6及以后，模拟文件系统，直接接触文件）

4.1 内核版本

运行中的内核

uname命令

uname - print system informationuname [OPTION]..
选项：
-n: 显示节点名称
-r: 显示VERSION-RELEASE
-a:	显示所有信息

4.2 内核模块命令

lsmod命令

• 显示由核心已经装载(已被使用的)的内核模块
• 显示的内容来自于: /proc/modules文件

modinfo命令

功能:管理内核模块

配置文件: /etc/modprobe.conf,/etc/modprobe.d/*.conf

显示模块的详细描述信息

modinfo [ -k kernel ] [ modulename | filename... ]

常用选项:

-n:只显示模块文件路径-
-p:显示模块参数
-a:作者
-d:描述

装载或卸载内核模块

modprobe [ -C config-file ] [ modulename ] [ module parame-ters... ]
modprobe [ -r ] modulename...

depmod命令: 内核模块依赖关系文件及系统信息映射文件的生成工具

insmod命令: 指定模块文件，不能自动解决依赖模块

insmod [ filename ] [ module options...]

范例:

insmod modinfo -n exportfs
Insmod modinfo -n xfs

rmmod命令:卸载模块，类似于modprobe -r

rmmod [ modulename ]

范例:

rmmod xfs
rmmod exportfs

4.3 编译内核

编译安装内核准备：

1. 准备好开发环境
2. 获取目标主机上硬件设备的相关信息
3. 获取目标主机系统功能的相关信息，例如:需要启用相应的文件系统
4. 获取内核源代码包，www.kernel.org

4.3.1 编译准备

4.3.1.1.目标主机硬件设备相关信息

CPU:

cat /proc/cpuinfo
x86info -a
lscpu

lsblk 块设备
全部硬件设备信息: hal-device: Centos 6

4.3.1.2 开发环境相关包

安装相对应包：gcc make ncurses-devel flex bison openssl-devel elfutils-libelf-devel

4.3.1.3 内核编译安装实现

1. 下载源码文件

2. 准备文本配置文件/boot/config-`uname-r`

3. make menuconfig: 配置内核选项，相当于./configure

   [ ] : N		#未启用
   [M]	: M		#存放在lib下的独立模块
   [*] : Y		#存放在核心里
   

4. make [-j #] 或者用以下两步实现

   make -j # bzlmage		#编译内核文件vmlinuz
   make -i # modules		#编译lib/modules下的文件
   

5. 安装模块: make modules_install

6. 安装内核相关文件: make install

   • 安装bzlmage为 /boot/vmlinuz-VERSION-RELEASE

   • 生成initramfs文件

   • 编辑grub的配置文件

4.3.1.4 编译安装内核实战案例

简述：

[root@CentOS8 ~]#yum -y install gcc make ncurses-devel flex bison openssl-devel elfutils-libelf-devel
[root@centos8 ~]#tar xf linux-5.4.13.tar.xz -C /usr/src
[root@centos8 ~]#cd /usr/src
[root@centos8 ~]#In -sv Tinux-5.4.13 Tinux
[rootacentos8 ~]#cd /usr/src/Tinux
[root@centos8 ~]#cp /boot/config-$(uname -r) ./.config
[root@centos8 ~]#vim .config
# CONFIG MODULE SIG is not set
CONFIG_SYSTEM_TRUSTED KEYS="
# CONFIG DEBUG INFO is not set
[rootacentos8 ~]#make hep
[rootacentos8 ~]#make menuconfig
[rootacentos8 ~]#make -j 2或者 make -j 2 bzImage ; make -j 2 modules
[rootacentos8 ~]#make modules install
[root@centos8 ~]#make install
[root@centos8 ~]#reboot

例：为C8安装最新内核6.4.11

[root@CentOS8 ~]#yum -y install gcc make ncurses-devel flex bison openssl-devel elfutils-libelf-devel
Last metadata expiration check: 1:31:08 ago on Sun 20 Aug 2023 10:37:38 PM CST.
Package gcc-8.5.0-4.el8_5.x86_64 is already installed.
Package make-1:4.2.1-10.el8.x86_64 is already installed.
Package ncurses-devel-6.1-9.20180224.el8.x86_64 is already installed.
Package openssl-devel-1:1.1.1k-5.el8_5.x86_64 is already installed.
Dependencies resolved.
===================================================================================================Package                         Architecture     Version                Repository           Size
===================================================================================================
Installing:bison                           x86_64           3.0.4-10.el8           AppStream           688 kelfutils-libelf-devel           x86_64           0.185-1.el8            BaseOS               59 kflex                            x86_64           2.6.1-9.el8            AppStream           320 kTransaction Summary
===================================================================================================
Install  3 PackagesTotal download size: 1.0 M
Installed size: 3.0 M
Downloading Packages:
(1/3): elfutils-libelf-devel-0.185-1.el8.x86_64.rpm                131 kB/s |  59 kB     00:00
(2/3): flex-2.6.1-9.el8.x86_64.rpm                                 339 kB/s | 320 kB     00:00
(3/3): bison-3.0.4-10.el8.x86_64.rpm                               569 kB/s | 688 kB     00:01
---------------------------------------------------------------------------------------------------
Total                                                              878 kB/s | 1.0 MB     00:01
Running transaction check
Transaction check succeeded.
Running transaction test
Transaction test succeeded.
Running transactionPreparing        :                                                                           1/1Installing       : elfutils-libelf-devel-0.185-1.el8.x86_64                                  1/3Installing       : flex-2.6.1-9.el8.x86_64                                                   2/3Running scriptlet: flex-2.6.1-9.el8.x86_64                                                   2/3Installing       : bison-3.0.4-10.el8.x86_64                                                 3/3Running scriptlet: bison-3.0.4-10.el8.x86_64                                                 3/3Verifying        : bison-3.0.4-10.el8.x86_64                                                 1/3Verifying        : flex-2.6.1-9.el8.x86_64                                                   2/3Verifying        : elfutils-libelf-devel-0.185-1.el8.x86_64                                  3/3Installed:bison-3.0.4-10.el8.x86_64   elfutils-libelf-devel-0.185-1.el8.x86_64   flex-2.6.1-9.el8.x86_64Complete![root@CentOS8 ~]#tar xvf linux-6.4.11.tar.xz -C /usr/local/src
[root@CentOS8 ~]#cd /usr/local/src
[root@CentOS8 src]#ls
httpd-2.4.57  httpd-2.4.57.tar.bz2  linux-6.4.11
[root@CentOS8 src]#du -sh .	#查看目录总大小
1.5G   
[root@CentOS8 src]#find -name "*.c" | wc -l	#.c后缀文件个数
32793
[root@CentOS8 src]#find -name "*.c" | xargs cat|wc -l		#所有.c文件总行数
23223391
[root@CentOS8 src]#cd linux-6.4.11/
[root@CentOS8 linux-6.4.11]#ls
arch     CREDITS        fs        ipc      lib          mm      samples   tools
block    crypto         include   Kbuild   LICENSES     net     scripts   usr
certs    Documentation  init      Kconfig  MAINTAINERS  README  security  virt
COPYING  drivers        io_uring  kernel   Makefile     rust    sound
[root@CentOS8 linux-6.4.11]#cp /boot/config-4.18.0-348.el8.x86_64 .config
[root@CentOS8 linux-6.4.11]#ls -a
.              .config        .get_maintainer.ignore  Kbuild       Makefile       scripts
..             COPYING        .gitattributes          Kconfig      mm             security
arch           CREDITS        .gitignore              kernel       net            sound
block          crypto         include                 lib          README         tools
certs          Documentation  init                    LICENSES     rust           usr
.clang-format  drivers        io_uring                .mailmap     .rustfmt.toml  virt
.cocciconfig   fs             ipc                     MAINTAINERS  samples[root@CentOS8 linux-6.4.11]#vim .config
# CONFIG_MODULE_SIG is not set		#将其注释
CONFIG_SYSTEM_TRUSTED KEYS=""			#删除中间内容
# CONFIG DEBUG INFO is not set[root@CentOS8 linux-6.4.11]#make hel p
[root@CentOS8 linux-6.4.11]#make menuconfigHOSTCC  scripts/basic/fixdepHOSTCC  scripts/kconfig/mconf.oHOSTCC  scripts/kconfig/lxdialog/checklist.oHOSTCC  scripts/kconfig/lxdialog/inputbox.oHOSTCC  scripts/kconfig/lxdialog/menubox.oHOSTCC  scripts/kconfig/lxdialog/textbox.oHOSTCC  scripts/kconfig/lxdialog/util.oHOSTCC  scripts/kconfig/lxdialog/yesno.oHOSTCC  scripts/kconfig/confdata.oHOSTCC  scripts/kconfig/expr.oLEX     scripts/kconfig/lexer.lex.cYACC    scripts/kconfig/parser.tab.[ch]HOSTCC  scripts/kconfig/lexer.lex.oHOSTCC  scripts/kconfig/menu.oHOSTCC  scripts/kconfig/parser.tab.oHOSTCC  scripts/kconfig/preprocess.oHOSTCC  scripts/kconfig/symbol.oHOSTCC  scripts/kconfig/util.oHOSTLD  scripts/kconfig/mconf
.config:569:warning: symbol value 'm' invalid for I8K
.config:3027:warning: symbol value 'm' invalid for ISDN_CAPI
.config:6142:warning: symbol value 'm' invalid for VFIO_VIRQFD
configuration written to .config*** End of the configuration.
*** Execute 'make' to start the build or try 'make help'.[root@CentOS8 linux-6.4.11]#make -j 2或者 make -j 8 bzImage ; make -j 8 modules
[root@CentOS8 linux-6.4.11]#time make -j 16 ;date		#计时
real    71m7.093s
user    315m20.782s
sys     57m0.485s
Mon Aug 21 01:45:32 CST 2023[rootacentos8 ~]#make modules_install
[root@CentOS8 linux-6.4.11]# ls /lib/modules/
4.18.0-348.el8.x86_64  6.4.11joyce-linux-6-4-11
[root@CentOS8 linux-6.4.11]#du -sh /lib/modules/6.4.11joyce-linux-6-4-11/
4.7G    /lib/modules/6.4.11joyce-linux-6-4-11/[root@centos8 ~]#make install
[root@centos8 ~]#reboot

make menuconfig：

修改完后查看.config文件，NTFS已经被修改

4.3.1.4 内核编译说明

1.配置内核选项:

支持“更新”模式进行配置: make help

• (a) make config: 基于命令行以遍历的方式配置内核中可配置的每个选项
• (b) make menuconfig: 基于curses的文本窗口界面
• © make gconfig: 基于GTK(GNOME) 环境窗口界面
• (d) make xconfig: 基于QT(KDE)环境的窗口界面

支持“全新配置”模式进行配置

• (a)make defconfig: 基于内核为目标平台提供的“默认”配置进行配置
• (b) make allyesconfig: 所有选项均回答为"yes"
• © make allnoconfig: 所有选项均回答为"no"

2.编译内核

• 全编译:

  make [-j #]
  

• 编译内核的一部分功能:

  (a)只编译某子目录中的相关代码

  cd /usr/src/linux; make dir/
  

  (b) 只编译一个特定的模块

  cd /usr/src/linux; make dir/file.ko
  

• 范例: 只为e1000编译驱动:

make drivers/net/ethernet/intel/e1000/e1000.ko

3 交叉编译内核

编译的目标平台与当前平台不相同

make	ARCH=arch name

要获取特定目标平台的使用帮助

make	ARCH=arch_name help

示例:

make ARCH=arm help

4重新编译需要事先清理操作

make clean: 清理大多数编译生成的文件，但会保留.config文件等
make mrproper: 清理所有编译生成的文件、config及某些备份文件
make distclean: 包含make mrproper，并清理patches以及编辑器备份文件

4.3.1.5 卸载内核

• 删除/usr/src/linux/目录下不需要的内核源码
• 删除/lib/modules/目录下不需要的内核库文件
• 删除/boot目录下启动的内核和内核映像文件
• 更改grub的配置文件，删除不需要的内核启动列表 grub2-mkconfig -o /boot/grub2/grub.cfg
• CentOS 8 还需要删除 /boot/loader/entries/5b85fc7444b240a992c42ce2a9f65db5-新内核版本.conf

5 Busybox

5.1 Busybox介绍

Busybox 最初是由 Bruce Perens 在 1996 年为 Debian GNU/Linux 安装盘编写的。其目标是在一张软盘(存储空间只有1MB多)上创建一个GNU/Linux 系统，可以用作安装盘和急救盘

Busybox 是一个开源项目，遵循GPL 2协议。Busybox将众多的UNIX命令集合进一个很小的可执行程序中，可以用来替代GNU fileutils、shellutils 等工具集。Busybox中各种命令与相应的GNU工具相比所能提供的选项比较少，但是也足够一般的应用了。Busybox主要用于嵌入式系统

Busybox 是一个集成了三百多个最常用Linux命令和工具的软件。BusyBox 包含了一些简单的工具，例如Is、cat和echo等等，还包含了一些更大、更复杂的工具，例grep、find、mount以及telnet。有些人将BusyBox 称为 Linux 工具里的瑞士军刀。简单的说BusyBox就好像是个大工具箱，它集成压缩了Linux 的许多工具和命令，也包含了 Android 系统的自带的shell

定制小型的Linux操作系统: inux内核+busybox

官方网站: https://busybox.net/

5.2 Busybox使用

busybox 的编译过程与Linux内核的编译类似

busybox的使用有三种方式

• busybox后直接跟命令，如 busybox ls
• 直接将busybox重命名，如 p busybox tar
• 创建符号链接，如 In -s busybox rm

busybox的安装

以上方法中，第三种方法最方便，但为busybox中每个命令都创建一个软链接，相当费事，busybox提供自动方法: busybox编译成功后，执行make install，则会产生一个 install目录，其中包含了busybox及每个命令的软链接

5.3 busybox编译安装

[root@centos7 ~]#yum -y install gcc gcc-c++ glibc glibc-devel make pcre pcre-devel openssl openssl-devel systemd-devel zlib-devel glibc-static ncurses-devel[root@centos7 ~]#wget https://busybox.net/downloads/busybox-1.36.1.tar.bz2
[root@centos7 ~]#tar xvf busybox-1.36.1.tar.bz2
[root@centos7 ~]#cd busybox-1.36.1/
[root@centos7 ~]#make menuconfig 按下面选择，把busybox编译也静态二进制、不用共享库
#Settings -->Build options -->[*] Build BusyBox as a static binary (no sharedTibs)
[root@centos7 ~]#make && make install#如果出错，执行make clean后，重新执行上面命令
[root@centos7 ~]#mkdir /mnt/sysroot/
[root@centos7 ~]#cp -a _install/* /mnt/sysroot/

6 systemd

6.1 systemd 特性

Systemd: 从 C 7 版本之后开始用 systemd 实现init进程，系统启动和服务器守护进程管理器，负责在系统启动或运行时，激活系统资源，服务器进程和其它进程

Systemd新特性

• 系统引导时实现服务并行启动
• 按需启动守护进程
• 自动化的服务依赖关系管理
• 完全代替xinetd
• 同时采用socket式与D-Bus总线式激活服务
• socket与服务程序分离
• 向后兼容sysv init脚本
• 使用systemctl 命令管理，systemctl命令固定不变，不可扩展，非由systemd启动的服务
• systemctl无法与之通信和控制
• 系统状态快照

systemd核心概念: unit

unit表示不同类型的systed对象，通过配置文件进行标识和配置;文件中主要包含了系统服务、监听socket、保存的系统快照以及其它与init相关的信息

Unit类型

#查看unit类型
systemctl -t help[root@CentOS7 yum.repos.d]#systemctl -t help
Available unit types:
service
socket
busname
target
snapshot
device
mount
automount
swap
timer
path
slice
scope

• service unit: 文件扩展名为.service，用于定义系统服务
• Target unit: 文件扩展名为.target，用于模拟实现运行级别
• Device unit: .device，用于定义内核识别的设备
• Mount unit:.mount， 定义文件系统挂载点
• Socket unit:.socket， 定义进程间通信用的socket文件，也可在系统启动时，延迟启动服务，实现按需启动
• Snapshot unit: .snapshot，管理系统快照
• Swap unit: .swap，用于标识swap设备
• Automount unit: .automount，文件系统的自动挂载点
• Path unit:.path，用于定义文件系统中的一个文件或目录使用，常用于当文件系统变化时，延时激活服务，如: spool 目录

unit的配置文件

/usr/lib/systemd/system;每个服务最主要的启动脚本设置，类似于之前的/etc/init.d/
/lib/systemd/system; ：Ubuntu的对应目录/run/systemd/system; 系统执行过程中所产生的服务脚本，比上面目录优先运行
/etc/systemd/system; 管理员建立的执行脚本，类似于/etc/rcN.d/sxx的功能，比上面目录优先运行

6.2 systemctl管理系统服务service unit

命令

systemctl COMMAND name.service

例：

#启动:相当于service name start
systemctl start name.service#停止: 相当于service name stop
systemctl stop name.service#重启:相当于service name restart
systemctl restart name.service#查看状态: 相当于service name status
systemctl status name.service#禁止自动和手动启动:
systemctl mask name.service#取消禁止
systemctl unmask name.service#查看某服务当前激活与否的状态:
systemctl is-active name.service#查看所有已经激活的服务:
systemctl list-units --type-t service#查看所有服务:
systemctl list-units --type service --all|-a#设定某服务开机自启，相当于chkconfig name on
systemctl enable name.service#设定某服务开机禁止启动: 相当于chkconfig name off
systemctl disable name.service#立即启动某服务，并设置为开机自启
systemctl enable --now name.service#立即关闭某服务，并设置为开机不启动
systemctl disable --now name.service#查看所有服务的开机自启状态，相当于chkconfig --list
systemctl list-unit-files --type service#用来列出该服务在哪些运行级别下启用和禁用: chkconfig -list name
Is /etc/systemd/system/*.wants/name.service#查看服务是否开机自启:
systemctl is-enabled name.service#列出失败的服务
systemctl --failed --type=service#查看服务的依赖关系:
systemctl list-dependencies name.service#杀掉进程:
systemctl kill unitname

服务状态

#显示状态
systemctl list-unit-files --type service --all

• loaded Unit配置文件已处理
• active(running) 一次或多次持续处理的运行
• active(exited) 成功完成一次性的配置
• active(waiting) 运行中，等待一个事件
• inactive 不运行
• enabled 开机启动
• disabled 开机不启动
• static 开机不启动，但可被另一个启用的服务激活
• indirect 重定向到别处

例：

#显示所有单元状态
systemctl 或 systemctl list-units#只显示服务单元的状态
systemctl --type=service#显示sshd服务单元
systemctl -l status sshd.service#验证sshd服务当前是否活动
systemctl is-active sshd#启动，停止和重启sshd服务
systemct] start sshd.service
systemctl stop sshd.service
systemctT restart sshd.service#重新加载配置
systemct reload sshd.service#列出活动状态的所有服务单元
systemctl list-units --type=service#列出所有服务单元
systemctl list-units --type=service --all#查看服务单元的启用和禁用状态
systemctl list-unit-files --type=service#列出依赖的单元
systemctl list-dependencies sshd#验证sshd服务是否开机启动
systemctl is-enabled sshd#禁用network，使之不能自动启动，但手动可以
systemctl disable network#启用network
systemct] enabe network#禁用network，使之不能手动或自动启动
systemctl mask network#启用network
systemct] unmask network

6.3 service unit文件格式

/etc/systemd/system: 系统管理员和用户使用
/usr/lib/systemd/system: 发行版打包者使用

帮助参考:

systemd.directives (7)，systemd.unit(5)，systemd.service(5)， systemd.socket(5)，systemd.target(5)，systemd.exec(5)

unit 格式说明:

• 以“#”开头的行后面的内容会被认为是注释
• 相关布尔值，1、yes、on、true 都是开启，0、no、off、false 都是关闭
• 时间单位默认是秒，所以要用毫秒 (ms)分钟 (m) 等须显式说明

service unit file文件通常由三部分组成**

[Unit]: 定义与Unit类型无关的通用选项;用于提供unit的描述信息、unit行为及依赖关系等
[Service]: 与特定类型相关的专用选项; 此处为Service类型
[Install]: 定义由“systemctl enable”以及”systemctl disable”命令在实现服务启用或禁用时用到的一些选项

Unit段的常用选项:

Description: 描述信息
After: 定义unit的启动次序，表示当前unit应该晚于哪些unit启动，其功能与Before相反
Requires: 依赖到的其它units，强依赖，被依赖的units无法激活时，当前unit也无法激活
Wants:依赖到的其它units，弱依赖
Conflicts: 定义units间的冲突关系

Service段的常用选项:

Type:定义影响ExecStart及相关参数的功能的unit进程启动类型simple: 默认值，这个daemon主要由ExecStart接的指令串来启动，启动后常驻于内存中forking: 由ExecStart启动的程序透过spawns延伸出其他子程序来作为此daemon的主要服务。原生父程序在启动结束后就会终止oneshot: 与simple类似，不过这个程序在工作完毕后就结束了，不会常驻在内存中dbus: 与simple类似，但这个daemon必须要在取得一个D-Bus的名称后，才会继续运作.因此通常也要同时设定BusNname= 才行onotify: 在启动完成后会发送一个通知消息。还需要配合 NotifyAccess 来让Systemd 接收消息idle: 与simple类似，要执行这个daemon必须要所有的工作都顺利执行完毕后才会执行。这类的daemon通常是开机到最后才执行即可的服务EnvironmentFile:环境配置文件
ExecStart:指明启动unit要运行命令或脚本的绝对路径
ExecStartPre:ExecStant前运行
ExecStartPost：ExecStart后运行
ExecStop:指明停止unit要运行的命令或脚本
Restart: 当设定Restart=1 时，则当次daemon服务意外终止后，会再次自动启动此服务
PrivateTmp: 设定为yes时，会在生成/tmp/systemd-private-UUID-NAME.service-XXXXX/tmp/目录

Install段的常用选项:

Alias: 别名，可使用systemctl command Alias.service
RequiredBy: 被哪些units所依赖，强依赖
WantedBy:被哪些units所依赖，弱依赖
Also: 安装本服务的时候还要安装别的相关服务

注意:对于新创建的unit文件，或者修改了的unit文件，要通知systemd重载此配置文件，而后可以选择重启

systemctl daemon-reToad

范例: 服务Unit文件——http

[unit]
Description=The Nginx HTTP Server daemon # 描述信息
After=network.target remote-fs.target nss-lookup.target # 指定启动nginx之前需要其他的其他服务，如network.target等[service]
# Type为服务类型，仅启动一个主进程的服务为simple，需要启动若干子进程的服务为forking
Type=forking# 设置执行systemctl start nginx后需要启动的具体命令
Execstart=/usr/ocal/nginx/sbin/nginx# 设置执行systemctl reload nginx后需要执行的具体命令
ExecReToad=/usr/local/nginx/sbin/nginx -s reload# 设置执行systemctl stop nginx后需要执行的具体命令
Execstop=/bin/kill -s OUIT ${MAINPID}[Install]
# 设置在什么模式下被安装，设置开机启动的时候需要
wantedBy=multi-user.target

范例: 服务Unit文件示例——tomcat

vim /usr/lib/systemd/system/tomcat.service
[unit]
Description=java tomcat project
After=sysTog.target network.target[service]
Type=forking
EnvironmentFile=/usr/local/tomcat/conf/tomcat.conf
Execstart=/usr/local/tomcat/bin/startup.sh
Execstop=/usr/local/tomcat/bin/shutdown.sh
PrivateTmp=true
User=tomcat[Install]
wantedBy=multi-user.target

**范例: 服务Unit文件示例——**bak

vim /etc/systemd/system/bak.service
[unit]
Description=backup /etc
Requires=atd.service[service]
Type=simple
Execstart=/bin/bash -c "echo /data/bak.sh | at now"[Install]
WantedBy=multi-user.target
systemctl daemon-reload
systemctl start bak

范例: Ubutun实现开机自动运行程序

[root@ubuntu1804 ~]#vim /etc/rc.local
[root@ubuntu1804 ~]#cat /etc/rc.local
#!/bin/bash
echo -e ' E[31;1mstarting test service E[Om
sleep 10
[root@ubuntu1804 ~]#chmod +x /etc/rc.local

6.4 运行级别

target units: 相当于CentOS 6之前的runlevel，unit配置文件: target

ls /usr/lib/systemd/system/*.target
systemctl list-unit-files --type target --a77

和运行级别对应关系

0 ==> runlevel0.target，poweroff.target
1 ==> runlevel1.target，rescue.target
2 ==> runlevel2.target，multi-user.target
3 ==> runlevel3.target，multi-user.target
4 ==> runlevel4.target，multi-user.target
5 ==> runlevel5.target，graphical.target
6 ==> runlevel6.target，reboot.target

查看依赖性:

systemct1 1ist-dependencies graphical.target

级别切换: 相当于 init N

systemct1 isolate name.target

进入默认target

systemct7 defau7t

范例:

#切换至字符模式

systemct] isolate multi-user.target

注意:只有/lib/systemd/system/*.target文件中Allowlsolate=yes 才能切换(修改文件需执行systemd daemon-reload才能生效)

获取默认运行级别:相当于查看 /etc/inittab

systemct1 get-defaut

修改默认级别: 相当于修改 /etc/inittab

systemct1 set-default name.target

范例:

[root@centos8 ~]#systemctl set-default multi-user.target
[root@centos8 ~]#ls -l /etc/systemd/system/default.target
lrwxrwxrwx. 1 root root 37 NoV 7 19:32 /etc/systemd/system/default.target	-> /1ib/systemd/system/multi-user.target

切换至紧急救援模式

systemct1 rescue

切换至emergency模式

systemctl emergency

说明: rescue.target 比emergency 支持更多的功能，例如日志等

传统命令init，poweroff，halt，reboot都成为systemctl的软链接

#关机
systemct1 halt、systemct1 poweroff#重启:
systemctl reboot#挂起:
systemct1 suspend#休眠:
systemct7
hibernate
#休眠并挂起:
systemct1 hybrid-sTeep

范例: 禁用ctrl+alt+delete 重启快捷键

[root@centos8 ~]#ls -l /1ib/systemd/system/ctrl-alt-del.target
lrwxrwxrwx. 1 root root 13 May 23 2019 /1ib/systemd/system/ctrl-alt-del.target -> reboot.target
[root@centos8 ~]#systemct1 mask ctrl-alt-de1.target
Created symlink /etc/systemd/system/ctr]-alt-del.target - /dev/nul1
[root@centos8 ~]#init q
[root@centos8 ~]#systemctl daemon-reload

6.5 Centos 7之后版本引导顺序

1. UEFi或BIOS初始化，运行POST开机自检

2. 选择启动设备

3. 引导装载程序,centos7是grub2,加载装载程序的配置文件

   ​ /etc/grub.d/

   ​ /etc/default/grub

   ​ /boot/grub2/grub.cfg

4. 加载initramfs驱动模块

5. 加载内核选项

6. 内核初始化，centos7使用systemd代替init

7. 执行initrd.target所有单元，包括挂载/etc/fstab

8. 从initramfs根文件系统切换到磁盘根目录

9. systemd执行默认target配置，配置文件/etc/systemd/system/default.target

10. systemd执行sysinit.target初始化系统及basic.target准备操作系统

11. systemd启动multi-user.target下的本机与服务器服务

12. systemd执行multi-user.target下的/etc/rc.d/rc.local

13. Systemd执行multi-user.target下的getty.target及登录服务

14. systemd执行graphical需要的服务

通过systemd-analyze 工具可以了解启动的详细过程

[root@CentOS8 ~]#systemd-analyze blame40.827s dnf-makecache.service6.374s plymouth-quit-wait.service5.407s cockpit-motd.service3.263s unbound-anchor.service2.570s mysqld.service1.543s tuned.service1.443s postfix.service1.373s systemd-udev-settle.service1.329s vdo.service1.038s sssd.service796ms polkit.service777ms ModemManager.service679ms initrd-switch-root.service674ms lvm2-monitor.service553ms NetworkManager-wait-online.service516ms avahi-daemon.service429ms NetworkManager.service426ms smartd.service425ms dracut-initqueue.service258ms autofs.service202ms cups.service180ms packagekit.service175ms accounts-daemon.service171ms udisks2.service168ms systemd-udev-trigger.service163ms bluetooth.service159ms systemd-logind.service143ms systemd-tmpfiles-clean.service133ms systemd-udevd.service125ms [e-mail]116ms sysroot.mount100ms sshd.service100ms rsyslog.service83ms initrd-parse-etc.service82ms gdm.service74ms systemd-tmpfiles-setup-dev.service69ms systemd-vconsole-setup.service68ms cockpit.service68ms sysstat-summary.service68ms systemd-modules-load.service61ms auditd.service59ms systemd-journald.service58ms nis-domainname.service57ms kmod-static-nodes.service56ms sys-kernel-debug.mount56ms boot.mount53ms dev-disk-by\x2duuid-80ee59c8\x2db184\x2d4f49\x2d9039\x2d5150257143b8.swap53ms systemd-remount-fs.service48ms plymouth-switch-root.service47ms systemd-fsck@dev-disk-by\x2duuid-54ead45a\x2d7577\x2d4b54\x2d9de2\x2d501aef04207a>42ms dracut-pre-pivot.service41ms dracut-cmdline.service41ms data.mount40ms dev-hugepages.mount37ms iscsi-shutdown.service36ms dev-mqueue.mount33ms systemd-user-sessions.service33ms systemd-journal-flush.service33ms systemd-tmpfiles-setup.service31ms rtkit-daemon.service40.827s dnf-makecache.service6.374s plymouth-quit-wait.service5.407s cockpit-motd.service3.263s unbound-anchor.service2.570s mysqld.service1.543s tuned.service1.443s postfix.service1.373s systemd-udev-settle.service1.329s vdo.service1.038s sssd.service796ms polkit.service777ms ModemManager.service679ms initrd-switch-root.service674ms lvm2-monitor.service553ms NetworkManager-wait-online.service516ms avahi-daemon.service429ms NetworkManager.service426ms smartd.service425ms dracut-initqueue.service258ms autofs.service202ms cups.service180ms packagekit.service175ms accounts-daemon.service171ms udisks2.service168ms systemd-udev-trigger.service163ms bluetooth.service159ms systemd-logind.service143ms systemd-tmpfiles-clean.service133ms systemd-udevd.service125ms [e-mail]116ms sysroot.mount100ms sshd.service100ms rsyslog.service83ms initrd-parse-etc.service82ms gdm.service74ms systemd-tmpfiles-setup-dev.service69ms systemd-vconsole-setup.service68ms cockpit.service68ms sysstat-summary.service68ms systemd-modules-load.service61ms auditd.service59ms systemd-journald.service58ms nis-domainname.service57ms kmod-static-nodes.service56ms sys-kernel-debug.mount56ms boot.mount53ms dev-disk-by\x2duuid-80ee59c8\x2db184\x2d4f49\x2d9039\x2d5150257143b8.swap53ms systemd-remount-fs.service48ms plymouth-switch-root.service47ms systemd-fsck@dev-disk-by\x2duuid-54ead45a\x2d7577\x2d4b54\x2d9de2\x2d501aef04207a>42ms dracut-pre-pivot.service41ms dracut-cmdline.service41ms data.mount40ms dev-hugepages.mount37ms iscsi-shutdown.service36ms dev-mqueue.mount33ms systemd-user-sessions.service33ms systemd-journal-flush.service33ms systemd-tmpfiles-setup.service31ms rtkit-daemon.service30ms sysstat.service30ms systemd-random-seed.service28ms systemd-sysctl.service22ms import-state.service20ms dracut-pre-udev.service19ms plymouth-read-write.service18ms initrd-cleanup.service17ms plymouth-start.service17ms cockpit.socket15ms plymouth-quit.service14ms proc-sys-fs-binfmt_misc.mount14ms cockpit-wsinstance-https-factory.socket14ms systemd-fsck-root.service13ms systemd-rfkill.service12ms sys-fs-fuse-connections.mount11ms cockpit-wsinstance-http.socket9ms systemd-update-utmp.service9ms [e-mail]7ms systemd-update-utmp-runlevel.service6ms dracut-shutdown.service5ms initrd-udevadm-cleanup-db.service5ms sysstat-collect.service2ms sys-kernel-config.mount1ms cockpit-wsinstance-http-redirect.socket
lines 61-84/84 (END)30ms sysstat.service30ms systemd-random-seed.service28ms systemd-sysctl.service22ms import-state.service20ms dracut-pre-udev.service19ms plymouth-read-write.service18ms initrd-cleanup.service17ms plymouth-start.service17ms cockpit.socket15ms plymouth-quit.service14ms proc-sys-fs-binfmt_misc.mount14ms cockpit-wsinstance-https-facto>14ms systemd-fsck-root.service13ms systemd-rfkill.service
lines 61-74/84 87%30ms sysstat.service30ms systemd-random-seed.service28ms systemd-sysctl.service22ms import-state.service20ms dracut-pre-udev.service19ms plymouth-read-write.service18ms initrd-cleanup.service17ms plymouth-start.service17ms cockpit.socket15ms plymouth-quit.service14ms proc-sys-fs-binfmt_misc.mount14ms cockpit-wsinstance-https-factory.socket14ms systemd-fsck-root.service13ms systemd-rfkill.service12ms sys-fs-fuse-connections.mount11ms cockpit-wsinstance-http.socket9ms systemd-update-utmp.service9ms [e-mail]7ms systemd-update-utmp-runlevel.service6ms dracut-shutdown.service5ms initrd-udevadm-cleanup-db.service5ms sysstat-collect.service2ms sys-kernel-config.mount1ms cockpit-wsinstance-http-redirect.socket
lines 61-84/84 (END)#或xml文件
[root@CentOS8 ~]#systemd-analyze plot > boot.xml
然后传到win下，用浏览器打开

[外链图片转存失败,源站可能有防盗链机制,建议将图片保存下来直接上传(img-xvJxmwXs-1692688111234)(C:\Users\HUIO\AppData\Roaming\Typora\typora-user-images\image-20230822120113748.png)]

6.6 设置内核参数

设置内核参数，只影响当次启动

启动时，到启动菜单，按e键，找到在linux 开头的行后添加systemd.unit=desired.target

例如：

 systemd.unit=emergency.target 或 systemd.unit=rescue.target

6.7 破解 CentOS 7和8的 root 密码

方法一

启动时任意键暂停启动
按e键进入编辑模式
将光标移动linux 开始的行(C7是Linux16那行	)，添加内核参数rd.break
按ctrl-x启动
mount -o remount,rw /sysroot
chroot /sysroot
passwd root#如果SELinux是启用的,才需要执行下面操作，如查没有启动，不需要执行
touch /.autorelabelexit
reboot

方式二

启动时任意键暂停启动
按e键进入编辑模式
将光标移动linux 开始的行，改为rw init=/sysroot/bin/sh
按ctrl-x启动
chroot /sysroot
passwd root#如果SELinux是启用的,才需要执行下面操作,如查没有启动,不需要执行
touch /.autorelabelexit
reboot

6.8 实现GRUB2安全

#添加grub密码
[root@CentOS8 ~]#grub2-setpassword
Enter password:
Confirm password:
#查看文件
[root@CentOS8 ~]#ll /boot/grub2/
total 340
-rw-r--r--. 1 root root     64 May 30 23:36 device.map
drwxr-xr-x. 2 root root   4096 May 30 23:36 fonts
-rw-r--r--. 1 root root   6590 Jul 25 15:05 grub.cfg
-rw-------  1 root root   1024 Aug 16 13:51 grubenv
drwxr-xr-x. 2 root root  12288 May 30 23:36 i386-pc
-rw-r--r--  1 root root 309444 Aug 18 21:48 logo.xpm
-rw-------  1 root root    298 Aug 22 12:21 user.cfg
[root@CentOS8 ~]#cat /boot/grub2/user.cfg
GRUB2_PASSWORD=grub.pbkdf2.sha512.10000.0DCB0C5B0F0A9B3021C99E920A0731164C713BCA004314B049811590E32A84348686B899E6D161D11D6C663C10A0C33100BE582B7BA5CF39C5919E845D9AEA6B.4AF8E233565BF8508115991D41FCCB2B3387E35807D5BE510744A86AD64F7C0CB79CE1166AFAB1186E957D10060DFAD1CA6B57C067815CE744175070E5FD501D
#清空grub密码
[root@centos8 ~]#at /dev/null > /boot/grub2/user.cfg

6.9 修复GRUB2

GRUB2: Centos 7，8及ubuntu1804都使用

引导提示时可以使用命令行界面，可从文件系统引导

主要配置文件: /boot/grub2/grub.cfg修复配置文件: grub2-mkconfig > /boot/grub2/grub.cfg

修复grub

grub2-install /dev/sda	#BIOS环境
grub2-insta77				#UEFI环境

调整默认启动内核

#以下命令是修改 /boot/grub2/grubenv 实现
grub2-set-default 0			#适合C7，因为C8配置文件中不再存储内核对应的数字，不知道0、1对应的是哪个内核或者vim /etc/default/grub
GRUB_DEFAULT=0[root@CentOS8 ~]#cat /boot/grub2/grubenv		#默认启动内核
# GRUB Environment Block
saved_entry=34f09f8df29847998143d560b2af24fb-4.18.0-348.el8.x86_64	#修改为需要的内核即可，适合C8
kernelopts=root=UUID=f2c173be-7848-43e9-9d0b-da0f1841f93f ro resume=UUID=80ee59c8-b184-4f49-9039-5150257143b8 rhgb quiet net.ifnames=0
boot_success=1
boot_indeterminate=0
########################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################################[root@CentOS8 ~]#cd
[root@CentOS8 ~]#ls /boot/loader/entries/		#查看所有内核
34f09f8df29847998143d560b2af24fb-0-rescue.conf
34f09f8df29847998143d560b2af24fb-4.18.0-348.el8.x86_64.conf

6.10 故障排错实战案例

6.10.1 实战案例1: centos 7，8 破坏MBR后进行恢复

dd if=/dev/zero of=/dev/sda bs=1 count=446
光盘进入救援模式
grub2-instal1 --root-directory=/mnt/sysimage /dev/sda

6.10.2 实战案例2: entos 7，8删除/boot/grub2/*所有内容进行恢复

#光盘进入救援模式
chroot /mnt/sysimage
grub2-install /dev/sda
grub2-mkconfig -o /boot/grub2/grub.cfg

6.10.3 实战案例3: Centos 7，8 删除/boot/下所有文件后进行恢复

#1 光盘救援模式下安装grub2
特别说明: centos8 必须先grub，再安装kernel,否则安装kernel-core时会提示grub出错
chroot /mnt/sysimage
mount /dev/sr0 /mnt
grub2-install /dev/sda#2 安装kernel
#Centos 7
rpm -ivh /mnt/Packages/kernel-3.10.0-1062.e17.x86_64.rpm --force
#Centos 8
rpm -ivh /mnt/Baseos/Packages/kernel-core-4.18.0-147.e18.x86_64.rpm --force#3 修复grub配置文件
生成grub2.cfg文件
grub2-mkconfig -o /boot/grub2/grub.cfg#4 退出重启
exit
exit