linux救援模式使用、自制linux系统和linux内核编译

内容：
1、linux系统启动排错及恢复(救援模式的使用)
2、自制linux系统
3、编译linux内核

一、系统启动排错及恢复(救援模式的使用)
1、bootloader损坏恢复
(1)进入救援模式
(2)在shell中运行grub程序

sh 3.1#grub
grub>root (hdx,y)
grub>setup (hd0) # setup (hd0)就是把GRUB写到硬盘的MBR上。
grub>quit

这里的X，如果是一个盘，就是0，如果你所安装的linux的根分区在第二个硬盘上，那X就是1了；Y，就是装有linux系统所在的根分区。

总结：在rescue模式下可以重装GRUB引导程序，修复MBR扇区。

[16:54 root@Centos6.8~]# dd if=/dev/zero of=/dev/sda bs=30 count=1
1+0 records in
1+0 records out
30 bytes (30 B) copied, 0.00292207 s, 10.3 kB/s
[18:44 root@Centos6.8~]# reboot now

成功修复：




2、vmlinux内核损坏恢复
(1)删除kernel做实验，要加上--nodeps：忽略依赖关系
(2)开机进入救援模式
(3)把光盘挂载上（内核文件在光盘里），注意，不要把光盘直接挂载在/mnt下，会把真根系统给隐藏了
(4)rpm安装kernel包，注意，救援模式下的真正的根是在/mnt/sysimage下，所以rpm要加上选项--root=/mnt/sysimage(如果切换了根chroot，则不需要此参数)
(5)重启后恢复系统

[19:22 root@Centos6.8~]# rpm -q kernel
kernel-2.6.32-642.el6.x86_64
[19:31 root@Centos6.8~]# rpm -e kernel
error: Failed dependencies:
kernel >= 2.6.30 is needed by (installed) pulseaudio-0.9.21-24.el6.x86_64
kernel >= 2.6.17 is needed by (installed) autofs-1:5.0.5-122.el6.x86_64
kernel >= 2.6.14 is needed by (installed) fuse-2.8.3-5.el6.x86_64
kernel >= 2.6.32-33.el6 is needed by (installed) xorg-x11-drv-intel-2.99.917-0.4.20151111.el6.x86_64
kernel >= 2.6.32-33.el6 is needed by (installed) xorg-x11-drv-ati-7.6.1-2.el6.x86_64
kernel >= 2.6.32-358.2.1 is needed by (installed) irqbalance-2:1.0.7-8.el6.x86_64
kernel >= 2.6.12-1.1411_FC5 is needed by (installed) pcmciautils-015-4.2.el6.x86_64
kernel-drm-nouveau = 16 is needed by (installed) xorg-x11-drv-nouveau-1:1.0.12-1.el6.x86_64
[19:31 root@Centos6.8~]# rpm -e kernel --nodeps
grubby fatal error: unable to find a suitable template
grubby: doing this would leave no kernel entries. Not writing out new config.
warning:    erase unlink of /lib/modules/2.6.32-642.el6.x86_64/weak-updates failed: No such file or directory
warning:    erase unlink of /lib/modules/2.6.32-642.el6.x86_64/modules.order failed: No such file or directory
warning:    erase unlink of /lib/modules/2.6.32-642.el6.x86_64/modules.networking failed: No such file or directory
warning:    erase unlink of /lib/modules/2.6.32-642.el6.x86_64/modules.modesetting failed: No such file or directory
warning:    erase unlink of /lib/modules/2.6.32-642.el6.x86_64/modules.drm failed: No such file or directory
warnin g:    erase unlink of /lib/modules/2.6.32-642.el6.x86_64/modules.block failed: No such file or directory

无法进入系统：




进入救援模式：




安装kernel：




成功修复：




3、initramfs文件损坏恢复
(1)把initramfs文件删除，模拟initramfs文件损坏
(2)进入救援模式，chroot=/mnt/sysimage，再使用mkinitrd命令重新生成initramfs文件【注意，一定要在boot目录下使用该命令】
(3)重启即可

[19:58 root@Centos6.8/boot]# rm -f initramfs-2.6.32-642.el6.x86_64.img
[19:58 root@Centos6.8/boot]# reboot
Broadcast message from root@Centos6.8
(/dev/pts/0) at 19:58 ...
The system is going down for reboot NOW!
sh 3.1# mkinitrd /boot/initramfs-`uname -r`.img `uname -r`

4、/etc/fstab文件损坏恢复
(1)进入救援模式
(2)知道根在哪个分区就是直接把根挂载上，然后修改fstab文件，如果不知道根在哪个分区则需要逐一尝试挂载，直到找到根系统，然后修改fstab文件
(3)修改完后重启即可

[19:14 root@Centos6.8~]# rm -f /etc/fstab
[19:15 root@Centos6.8~]# reboot
Broadcast message from root@Centos6.8
(/dev/pts/0) at 19:15 ...
The system is going down for reboot NOW!

5、/boot目录文件误删除恢复
(1)挂载光盘
(2)安装kernel rpm -ivh --force（会同时生成initramfs）
(3)安装grub：grub-install （必须切换到真根目录运行该命令），但是没有grub.conf文件需要手动创建

总结：把boot分区删掉，实际是删除了kernel和grub，所以把kernel和grub安装上去即可，同时需要手工配置grub.conf文件

[19:22 root@Centos6.8/]# rm -rf /boot/
rm: cannot remove `/boot': Device or resource busy
[19:22 root@Centos6.8/]# ls /boot/
[19:22 root@Centos6.8/]# ls /boot/
[19:22 root@Centos6.8/]# ll /boot/
total 0

挂载光盘：




安装kernel：




安装grub(需要切换到真根)：







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二、自制linux系统
步骤概述：
1、新建一个硬盘
2、在该新硬盘上新建两个分区，一个当boot分区，一个当/分区
3、格式化并且挂载两个分区，注意，其中boot分区的挂载目录一定是boot名字的目录
4、在新硬盘安装grub（要使用--root-directory参数指定新硬盘的根分区），同时手动配置grub.conf配置文件
5、把kernel和initramfs文件放置boot分区
6、在根分区创建相应的目录
7、把一些常用命令拷贝至新硬盘的根分区，注意，同时要把二进制程序相应的库文件一并拷到新硬盘的lib文件夹（这里更加加深了二进制程序和库文件的关系，可以把库文件理解成二进制程序的函数）
8、把硬盘拆下，安装到新的虚拟机测试

步骤演示详解过程：
1、新建一个硬盘
2、在该新硬盘上新建两个分区，一个当boot分区，一个当/分区

[20:00 root@Centos6.8~]# fdisk /dev/sdb
WARNING: DOS-compatible mode is deprecated. It's strongly recommended to
switch off the mode (command 'c') and change display units to
sectors (command 'u').
Command (m for help): n
Command action
e   extended
p   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): +100M
Command (m for help): n
Command action
e   extended
p   primary partition (1-4)
p
Partition number (1-4): 2
First cylinder (15-2610, default 15):
Using default value 15
Last cylinder, +cylinders or +size{K,M,G} (15-2610, default 2610): +1G
Command (m for help): p
Disk /dev/sdb: 21.5 GB, 21474836480 bytes
255 heads, 63 sectors/track, 2610 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk identifier: 0xefd94e53
Device Boot      Start         End      Blocks   Id  System
/dev/sdb1               1          14      112423+  83  Linux
/dev/sdb2              15         146     1060290   83  Linux
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
Syncing disks.
[20:01 root@Centos6.8~]# 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   200M  0 part /boot
├─sda2   8:2    0  48.8G  0 part /
├─sda3   8:3    0  19.5G  0 part /testdir
├─sda4   8:4    0     1K  0 part
└─sda5   8:5    0   3.9G  0 part [SWAP]
sdb      8:16   0    20G  0 disk
├─sdb1   8:17   0 109.8M  0 part
└─sdb2   8:18   0     1G  0 part

3、格式化并且挂载两个分区，注意，其中boot分区的挂载目录一定是boot名字的目录

[20:04 root@Centos6.8~]# mkfs.ext4 /dev/sdb1
mke2fs 1.41.12 (17-May-2010)
Filesystem label=
OS type: Linux
Block size=1024 (log=0)
Fragment size=1024 (log=0)
Stride=0 blocks, Stripe width=0 blocks
28112 inodes, 112420 blocks
5621 blocks (5.00%) reserved for the super user
First data block=1
Maximum filesystem blocks=67371008
14 block groups
8192 blocks per group, 8192 fragments per group
2008 inodes per group
Superblock backups stored on blocks:
8193, 24577, 40961, 57345, 73729
Writing inode tables: done
Creating journal (4096 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 22 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
[20:05 root@Centos6.8~]# 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
66384 inodes, 265072 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, 229376
Writing inode tables: done
Creating journal (8192 blocks): done
Writing superblocks and filesystem accounting information: done
This filesystem will be automatically checked every 27 mounts or
180 days, whichever comes first.  Use tune2fs -c or -i to override.
[20:05 root@Centos6.8~]# mkdir /mnt/boot
[20:05 root@Centos6.8~]# mkdir /mnt/root
[20:05 root@Centos6.8~]# mount /dev//sdb1 /mnt/boot/
[20:05 root@Centos6.8~]# mount /dev//sdb2 /mnt/root/
[20:05 root@Centos6.8~]# df
Filesystem     1K-blocks    Used Available Use% Mounted on
/dev/sda2       50264772 5723488  41981284  12% /
tmpfs            1019184       0   1019184   0% /dev/shm
/dev/sda1         194241   33869    150132  19% /boot
/dev/sda3       20027260   44996  18958264   1% /testdir
/dev/sdb1         104769    1550     97598   2% /mnt/boot
/dev/sdb2        1010812    1304    956496   1% /mnt/root

4、在新硬盘安装grub，同时手动配置grub.conf配置文件

[20:08 root@Centos6.8/mnt/boot]# ls
lost+found
[20:08 root@Centos6.8/mnt/boot]# ll
total 12
drwx------. 2 root root 12288 Sep  9 20:05 lost+found
[20:09 root@Centos6.8/mnt/boot]# 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
[20:10 root@Centos6.8/mnt/boot]# ll
total 14
drwxr-xr-x. 2 root root  1024 Sep  9 20:10 grub
drwx------. 2 root root 12288 Sep  9 20:05 lost+found
[20:34 root@Centos6.8/mnt/root/lib]# cat !$
cat /mnt/boot/grub/grub.conf
default=0
timeout=5
title YOUR LINUX
root(hd0,0)
kernel /initramfs-2.6.32-642.el6.x86_64.img root=/dev/sda2 init=/bin/bash
initrd /vmlinuz-2.6.32-642.el6.x86_64

5、把kernel和initramfs文件放置boot分区

[20:10 root@Centos6.8/mnt/boot]# cp /boot/vmlinuz-2.6.32-642.el6.x86_64 /boot/initramfs-2.6.32-642.el6.x86_64.img .
[20:17 root@Centos6.8/mnt/boot]# ls
grub  initramfs-2.6.32-642.el6.x86_64.img  lost+found  vmlinuz-2.6.32-642.el6.x86_64

6、在根分区创建相应的目录

[20:17 root@Centos6.8/mnt/boot]# cd /mnt/root/
[20:18 root@Centos6.8/mnt/root]# ls
lost+found
[20:18 root@Centos6.8/mnt/root]# mkdir {etc,home,lib,lib64,usr,proc,sys,mnt,media,var,root,bin,sbin,tmp,dev}
[20:20 root@Centos6.8/mnt/root]# ls
bin  dev  etc  home  lib  lib64  lost+found  media  mnt  proc  root  sbin  sys  tmp  usr  var

7、把一些常用命令拷贝至新硬盘的根分区，注意，同时要把二进制程序相应的库文件一并拷到新硬盘的lib文件夹（这里更加加深了二进制程序和库文件的关系，可以把库文件理解成二进制程序的函数）
这里写了一个脚本来进行复制：

#!/bin/bash

ch_root="/mnt/root"
[ ! -d $ch_root ] && mkdir $ch_root

bincopy() {
if which $1 &>/dev/null; then
local cmd_path=`which --skip-alias $1`
local bin_dir=`dirname $cmd_path`
[ -d ${ch_root}${bin_dir} ] || mkdir -p ${ch_root}${bin_dir}
[ -f ${ch_root}${cmd_path} ] || cp $cmd_path ${ch_root}${bin_dir}
return 0
else
echo "Command not found."
return 1
fi
}

libcopy() {
local lib_list=$(ldd `which --skip-alias $1` | grep -Eo '/[^[:space:]]+')
for loop in $lib_list;do
local lib_dir=`dirname $loop`
[ -d ${ch_root}${lib_dir} ] || mkdir -p  ${ch_root}${lib_dir}
[ -f ${ch_root}${loop} ] || cp $loop ${ch_root}${lib_dir}
done
}

read -p "Please input a command or quit: " command

while [ "$command" != "quit" ];do
if bincopy $command ;then
libcopy $command
fi
read -p "Please input a command or quit: " command
done

[20:44 root@Centos6.8/mnt/root/etc]# tree /mnt/root/
/mnt/root/
├── bin
│   ├── bash
│   ├── df
│   ├── echo
│   ├── ls
│   ├── lsblk
│   └── mount
├── dev
├── etc
│   └── fstab
├── home
├── lib
│   ├── ld-linux-x86-64.so.2
│   ├── libacl.so.1
│   ├── libattr.so.1
│   ├── libblkid.so.1
│   ├── libcap.so.2
│   ├── libc.so.6
│   ├── libdl.so.2
│   ├── libpthread.so.0
│   ├── librt.so.1
│   ├── libselinux.so.1
│   ├── libsepol.so.1
│   ├── libtinfo.so.5
│   └── libuuid.so.1
├── lib64
├── lost+found
├── media
├── mnt
├── proc
├── root
├── sbin
├── sys
├── tmp
├── usr
└── var

8、把硬盘拆下，安装到新的虚拟机测试

三、编译linux内核
1、为什么需要编译内核
编译内核可能是出于某种需求，比如对内核大小有要求，去掉内核中某些用不到的部分，或者添加一些自己需要的部分，如ntfs文件系统，或者自己修改了某部分内核代码，需要编译后验证功能。
2、编译内核步骤
(1)到kernel.org下载需要编译的版本的内核源码包
(2)准备相应的开发编译环境：包组(CentOS 6)：
Server Platform Development
Development Tools
(2)把kernel拷贝到/usr/src目录下，并且解压放在linux的目录(一般编译会再/usr/src/linux目录进行，放在其他目录也可以)

[12:16 root@Centos6.8/usr/src]# ll
total 71504
drwxr-xr-x.  2 root root     4096 Sep 23  2011 debug
drwxr-xr-x.  3 root root     4096 Aug 26 19:03 kernels
drwxrwxr-x. 23 root root     4096 Aug 29 21:50 linux
-rw-r--r--.  1 root root 73207156 Aug 30  2013 linux-3.10.10.tar.xz

(3)进入/usr/src/linux目录，注意，一定要进入该目录，运行字符界面的模块选择界面命令make menuconfig，然后按需要选择需要的功能即可

[12:19 root@Centos6.8/usr/src/linux]# make menuconfig
.config - Linux/x86 3.10.10 Kernel Configuration
qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq
lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqq Linux/x86 3.10.10 Kernel Configuration qqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqk
x  Arrow keys navigate the menu.  <Enter> selects submenus --->.  Highlighted letters are hotkeys.  Pressing <Y> includes, <N>  x
x  excludes, <M> modularizes features.  Press <Esc><Esc> to exit, <?> for Help, </> for Search.  Legend: [*] built-in  [ ]      x
x  excluded  <M> module  < > module capable                                                                                     x
x                                                                                                                               x
x lqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqk x
x x                          [*] 64-bit kernel                                                                                x x
x x                              General setup  --->                                                                          x x
x x                          [*] Enable loadable module support  --->                                                         x x
x x                          -*- Enable the block layer  --->                                                                 x x
x x                              Processor type and features  --->                                                            x x
x x                              Power management and ACPI options  --->                                                      x x
x x                              Bus options (PCI etc.)  --->                                                                 x x
x x                              Executable file formats / Emulations  --->                                                   x x
x x                          -*- Networking support  --->                                                                     x x
x x                              Device Drivers  --->                                                                         x x
x x                              Firmware Drivers  --->                                                                       x x
x x                              File systems  --->                                                                           x x
x x                              Kernel hacking  --->                                                                         x x
x x                              Security options  --->                                                                       x x
x x                          -*- Cryptographic API  --->                                                                      x x
x x                          [*] Virtualization  --->                                                                         x x
x x                              Library routines  --->                                                                       x x
x mqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj x
tqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqu
x                                   <Select>    < Exit >    < Help >    < Save >    < Load >                                    x
mqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqqj

(4)保存好编译模块后，就可以进行内核的编译了（注意，请预留至少10G的空间，在编译的过程中会产生很多临时文件，同时编译时间长短根据机器性能决定）
make [-j #] ：#表示多少个CPU进行编译
make modules_install：安装模块
make install ：安装内核相关文件
重启

重启系统后即可看见编译的内核







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