首先说明：
[root@CentOS6 ~]# rm -rf / //这条命令不可以执行
[root@CentOS6 ~]# rm -rf /* //这条命令可以执行，别去试
ext4文件系统上误删除文件，可以用extundelete恢复。ext3恢复使用ext3grep。Windows恢复使用final data v2.0汉化版和easyrecovery等。
误删除文件后，第一件事是避免误删除的文件内容被覆盖，这时可以卸载需要恢复文件的分区或以只读的方式挂载。
(1).下载extundelete
https://sourceforge.net/ 开源软件发布中心
https://github.com/ github项目托管平台
(2).准备实验环境
VMare12 CentOS6.8 添加一块硬盘20G
不会看这里，Linux空硬盘从分区到挂载
这里创建sdb1分区，挂载到/newpar下。
还有将CentOS6.8的光盘镜像挂载到/mnt下。
(3).复制一些测试文件，然后删除，以备测试恢复。
这里为了更好的展示，安装一下tree。
[root@centos6 ~]# rpm -ivh /mnt/Packages/tree-1.5.3-3.el6.x86_64.rpm
warning: /mnt/Packages/tree-1.5.3-3.el6.x86_64.rpm: Header V3 RSA/SHA1 Signature, key ID c105b9de: NOKEY
Preparing... ########################################### [100%]
1:tree ########################################### [100%]
下面开始复制文件
[root@centos6 ~]# cp /etc/passwd /newpar/
[root@centos6 ~]# cp /etc/hosts /newpar/
[root@centos6 ~]# echo abc > a.txt
[root@centos6 ~]# mkdir -p /newpar/a/b/c/
[root@centos6 ~]# cp a.txt /newpar/a/
[root@centos6 ~]# cp a.txt /newpar/a/b/
[root@centos6 ~]# touch /newpar/a/b/test.txt
[root@centos6 ~]# tree /newpar/
/newpar/
├── a
│ ├── a.txt
│ └── b
│ ├── a.txt
│ ├── c //空的
│ └── test.txt //空的
├── hosts
├── lost+found
└── passwd
4 directories, 5 files
下面开始删除
[root@centos6 ~]# rm -rf /newpar/{a,hosts,passwd}
[root@centos6 ~]# ls /newpar/
lost+found
删完了，记得误删除第一步，卸载分区。如果是根目录看(7).扩展2
[root@centos6 ~]# umount /newpar/ //不能在挂载点下卸载
使用df -a查看文件系统的挂载点
[root@centos6 ~]# df -a
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/vg_centos6-lv_root
17938864 3958368 13062584 24% /
proc 0 0 0 - /proc
sysfs 0 0 0 - /sys
devpts 0 0 0 - /dev/pts
tmpfs 953652 72 953580 1% /dev/shm
/dev/sda1 487652 40913 421139 9% /boot
/dev/sr0 3824484 3824484 0 100% /mnt
none 0 0 0 - /proc/sys/fs/binfmt_misc
[root@centos6 ~]# mkdir /cdrom
[root@centos6 ~]# mount /dev/sr0 /cdrom/
mount: block device /dev/sr0 is write-protected, mounting read-only
[root@centos6 ~]# df -a
Filesystem 1K-blocks Used Available Use% Mounted on
/dev/mapper/vg_centos6-lv_root
17938864 3958372 13062580 24% /
proc 0 0 0 - /proc
sysfs 0 0 0 - /sys
devpts 0 0 0 - /dev/pts
tmpfs 953652 72 953580 1% /dev/shm
/dev/sda1 487652 40913 421139 9% /boot
/dev/sr0 3824484 3824484 0 100% /mnt
none 0 0 0 - /proc/sys/fs/binfmt_misc
/dev/sr0 3824484 3824484 0 100% /cdrom
(4).安装extundelete
将下载好的extundelete上传到服务器中。
[root@centos6 ~]# ls
anaconda-ks.cfg install.log 模板 文档 桌面
a.txt install.log.syslog 视频 下载
extundelete-0.2.4.tar.bz2 公共的 图片 音乐
解压
[root@centos6 ~]# tar -jxvf extundelete-0.2.4.tar.bz2 //-j过滤bz2格式
准备依赖包（我的CentOS6.8镜像好像不全，其实还可以用rpm -ivh安装gcc-c++和e2fsprogs-devel）
[root@centos6 extundelete-0.2.4]# yum -y install gcc-c++
[root@centos6 extundelete-0.2.4]# yum -y install e2fsprogs-devel
安装extundelete
[root@centos6 ~]# cd extundelete-0.2.4
[root@centos6 extundelete-0.2.4]# ./configure //检查系统安装环境，为了生成Makefile文件
Configuring extundelete 0.2.4
Writing generated files to disk
[root@centos6 extundelete-0.2.4]# make -j 4 //编译，把源代码编译成可执行的二进制文件。-j 4使用4进程或4核同时编译，提高编译速度。根据实际配置修改
make -s all-recursive
Making all in src
extundelete.cc:571: 警告：未使用的参数‘flags’
[root@centos6 extundelete-0.2.4]# make install //安装
Making install in src
/usr/bin/install -c extundelete '/usr/local/bin' //在此目录下
(5).恢复文件
创建一个文件夹，将恢复的文件保存到文件夹内
[root@centos6 ~]# umount /dev/sdb1 //确保卸载分区
umount: /dev/sdb1: not mounted
[root@centos6 ~]# mkdir test //创建test文件夹
[root@centos6 ~]# cd test/
[root@centos6 test]# ls
查看inode号
[root@centos6 test]# extundelete /dev/sdb1 --inode 2 //ext4文件系统分区根目录的inode值为2，xfs文件系统分区根目录的inode值为64。
NOTICE: Extended attributes are not restored.
Loading filesystem metadata ... 160 groups loaded.
Group: 0
Contents of inode 2:
0000 | ed 41 00 00 00 10 00 00 60 7b 2e 5c 4e 7b 2e 5c | .A......`{.\N{.\
0010 | 4e 7b 2e 5c 00 00 00 00 00 00 03 00 08 00 00 00 | N{.\............
0020 | 00 00 00 00 06 00 00 00 21 24 00 00 00 00 00 00 | ........!$......
0030 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................
0040 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................
0050 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................
0060 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................
0070 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................
0080 | 1c 00 00 00 a8 37 a3 c1 a8 37 a3 c1 7c d2 20 60 | .....7...7..|. `
0090 | 7a 72 2e 5c 00 00 00 00 00 00 00 00 00 00 00 00 | zr.\............
00a0 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................
00b0 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................
00c0 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................
00d0 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................
00e0 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................
00f0 | 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 | ................ Inode is Allocated
File mode: 16877
Low 16 bits of Owner Uid: 0
Size in bytes: 4096
Access time: 1546550112
Creation time: 1546550094
Modification time: 1546550094
Deletion Time: 0
Low 16 bits of Group Id: 0
Links count: 3
Blocks count: 8
File flags: 0
File version (for NFS): 0
File ACL: 0
Directory ACL: 0
Fragment address: 0
Direct blocks: 9249, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0
Indirect block: 0
Double indirect block: 0
Triple indirect block: 0 File name | Inode number | Deleted status
. 2
.. 2
lost+found 11
passwd 12 Deleted
hosts 13 Deleted
a 262145 Deleted
1）通过inode恢复
根据上面的inode值，使用--restore-inode选项恢复passwd
[root@centos6 test]# extundelete /dev/sdb1 --restore-inode 12
NOTICE: Extended attributes are not restored.
Loading filesystem metadata ... 160 groups loaded.
Loading journal descriptors ... 67 descriptors loaded.
[root@centos6 test]# ls -l
总用量 4
drwxr-xr-x. 2 root root 4096 1月 4 07:07 RECOVERED_FILES //可以看到一个新的文件夹
[root@centos6 test]# cd RECOVERED_FILES/
[root@centos6 RECOVERED_FILES]# ls
file.12 //这就是恢复出来的文件
[root@centos6 RECOVERED_FILES]# diff /etc/passwd file.12 //比较一下是否有不同。没有输出就是一样。
2）通过文件名恢复
也可以根据上面的文件名，使用--restore-file选项恢复passwd。这样还可以同时还原文件名
[root@centos6 test]# extundelete /dev/sdb1 --restore-file passwd
NOTICE: Extended attributes are not restored.
Loading filesystem metadata ... 160 groups loaded.
Loading journal descriptors ... 67 descriptors loaded.
Successfully restored file passwd
[root@centos6 test]# ls RECOVERED_FILES/
file.12 passwd //可以看到恢复出了一个名为passwd的文件
[root@centos6 test]# diff RECOVERED_FILES/file.12 RECOVERED_FILES/passwd //两个文件内容是一样的
3）恢复某个目录
使用--restore-directory选项恢复文件夹a。注意：空目录和空文件无法恢复
[root@centos6 test]# extundelete /dev/sdb1 --restore-directory a
NOTICE: Extended attributes are not restored.
Loading filesystem metadata ... 160 groups loaded.
Loading journal descriptors ... 67 descriptors loaded.
Searching for recoverable inodes in directory a ...
7 recoverable inodes found.
Looking through the directory structure for deleted files ...
3 recoverable inodes still lost. //3个可回收的inode仍然丢失
[root@centos6 test]# tree RECOVERED_FILES/a/
RECOVERED_FILES/a/
├── a.txt
└── b
└── a.txt //少了空文件夹c和空文件test.txt 1 directory, 2 files
4）恢复所有文件
使用--restore-all选项恢复所有文件。注意：空目录和空文件无法恢复
[root@centos6 test]# rm -rf *
[root@centos6 test]# ls
[root@centos6 test]# extundelete /dev/sdb1 --restore-all
NOTICE: Extended attributes are not restored.
Loading filesystem metadata ... 160 groups loaded.
Loading journal descriptors ... 67 descriptors loaded.
Searching for recoverable inodes in directory / ...
7 recoverable inodes found.
Looking through the directory structure for deleted files ...
0 recoverable inodes still lost.
[root@centos6 test]# tree RECOVERED_FILES/
RECOVERED_FILES/
├── a
│ ├── a.txt
│ └── b
│ └── a.txt //少了空目录c和空文件test.txt
├── hosts
└── passwd 2 directories, 4 files
(6).扩展1：
Linux文件系统由三部分组成：文件名，inode（存放文件元数据信息），block（真正存放数据）。Windows也由这三部分组成。
1）查看inode号
[root@CentOS6 ~]# ls -i anaconda-ks.cfg
137428 anaconda-ks.cfg
查看inode中的文件属性。通过stat命令查看inode中包含的内容
[root@CentOS6 ~]# stat anaconda-ks.cfg
File: "anaconda-ks.cfg"
Size: 1700 Blocks: 8 IO Block: 4096 普通文件
Device: fd00h/64768d Inode: 137428 Links: 1
Access: (0600/-rw-------) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2018-09-01 18:01:33.658648102 +0800
Modify: 2018-03-13 18:29:40.674999889 +0800
Change: 2018-03-13 18:29:48.813999887 +0800
2）Block块：真正存储数据的地方
为什么删除比复制块？因为一般的删除都是逻辑删除，只删除了文件名。当有新的文件占用inode和block，此时只有找专业的数据恢复公司，通过奇偶校验找回文件。
(7).扩展2：
如果想恢复根下删除的文件怎么办？
方法一：立即断电（因为正常关机会产生日志，防止日志对数据覆盖），然后把磁盘以只读方式挂在到另一台相同相同的电脑中进行恢复
方法二：把extundelete在另一台相同相同的电脑上安装好，然后复制到U盘中。把U盘插入服务器，恢复时将恢复的文件保存到U盘中（不要让恢复的数据写到根下，那样会覆盖之前删除的文件）