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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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