ex22
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# 练习 22:文件系统:移动数据,`tar`,`dd`
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> 原文:[Exercise 22. Filesystems: moving data around: tar, dd](https://archive.fo/JSknE)
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> 译者:[飞龙](https://github.com/wizardforcel)
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> 协议:[CC BY-NC-SA 4.0](http://creativecommons.org/licenses/by-nc-sa/4.0/)
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> 自豪地采用[谷歌翻译](https://translate.google.cn/)
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现在是时候自己看看了,Linux 中的所有东西只是一个文件。
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这个练习是一个很大的练习,但是看看你学到了什么。完成之后,在`man`中查看所有故意不解释的程序参数,,并试图自己解释每个命令的作用。
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现在你将学习如何玩转数据。
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## 这样做
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```
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1: tar -czvf root.tgz /opt/root/
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2: tar -tzvf root.tgz
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3: cd /tmp
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4: tar -zxvf ~/root.tgz
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5: ls -al
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6: dd_if=$(mount | grep /tmp | cut -d ' ' -f 1) && echo $dd_if
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7: sudo dd if=$dd_if of=~/tmp.img bs=10M
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8: cd && ls -alh
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9: sudo losetup /dev/loop1 ~/tmp.img && sudo mount /dev/loop1 /mnt/
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10: ls -al /mnt
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11: sudo umount /mnt && sudo losetup -d /dev/loop1
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12: sudo umount $dd_if && sudo mkfs.ext3 $dd_if
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13: new_uuid=$(sudo tune2fs -l $dd_if | awk '/UUID/{print $3}') && echo $new_uuid
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14: grep '/tmp' /etc/fstab
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15: sed "s/^UUID=.*\/tmp\s\+ext3\s\+defaults\s\+[0-9]\s\+[0-9]\s\?/UUID=$new_uuid \/tmp ext3 defaults 0 2/" /etc/fstab
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```
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现在使用`sudo tune2fs -l`和`sudo blkid`检查输出。如果`/etc/fstab`中的 UUID 替换看起来正常,执行实际的替换。
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```
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16: sudo sed -i'.bak' "s/^UUID=.*\/tmp\s\+ext3\s\+defaults\s\+[0-9]\s\+[0-9]\s\?/UUID=$new_uuid \/tmp ext3 defaults 0 2/" /etc/fstab
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17: sudo mount -a && ls /tmp
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18: sudo umount /tmp && pv ~/tmp.img | sudo dd of=$dd_if bs=10M
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19: new_uuid=$(sudo tune2fs -l $dd_if | awk '/UUID/{print $3}') && echo $new_uuid
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20: sudo sed -i'.bak' "s/^UUID=.*\/tmp\s\+ext3\s\+defaults\s\+[0-9]\s\+[0-9]\s\?/UUID=$new_uuid \/tmp ext3 defaults 0 2/" /etc/fstab
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21: sudo mount -a
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22: rm -v tmp.img
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```
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输入`y`并按下`<ENTER>`。
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## 你会看到什么
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```
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user1@vm1:~$ tar -czvf root.tgz /opt/root/
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tar: Removing leading '/' from member names
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/opt/root/
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/opt/root/bin/
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/opt/root/bin/bash
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/opt/root/lib64/
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/opt/root/lib64/ld-linux-x86-64.so.2
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/opt/root/lib/
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/opt/root/lib/libdl.so.2
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/opt/root/lib/libncurses.so.5
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/opt/root/lib/libc.so.6
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user1@vm1:~$ tar -tzvf root.tgz
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drwxr-xr-x root/root 0 2012-07-05 03:14 opt/root/
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drwxr-xr-x root/root 0 2012-07-05 03:14 opt/root/bin/
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-rwxr-xr-x root/root 926536 2012-07-05 03:14 opt/root/bin/bash
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drwxr-xr-x root/root 0 2012-07-05 03:14 opt/root/lib64/
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-rwxr-xr-x root/root 128744 2012-07-05 03:14 opt/root/lib64/ld-linux-x86-64.so.2
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drwxr-xr-x root/root 0 2012-07-05 03:14 opt/root/lib/
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-rw-r--r-- root/root 14696 2012-07-05 03:14 opt/root/lib/libdl.so.2
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-rw-r--r-- root/root 286776 2012-07-05 03:14 opt/root/lib/libncurses.so.5
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-rwxr-xr-x root/root 1437064 2012-07-05 03:14 opt/root/lib/libc.so.6
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user1@vm1:~$ cd /tmp
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user1@vm1:/tmp$ tar -zxvf ~/root.tgz
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opt/root/
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opt/root/bin/
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opt/root/bin/bash
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opt/root/lib64/
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opt/root/lib64/ld-linux-x86-64.so.2
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opt/root/lib/
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opt/root/lib/libdl.so.2
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opt/root/lib/libncurses.so.5
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opt/root/lib/libc.so.6
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user1@vm1:/tmp$ ls -al
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total 19
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drwxrwxrwt 6 root root 1024 Jul 5 04:17 .
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drwxr-xr-x 22 root root 1024 Jul 3 08:29 ..
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drwxrwxrwt 2 root root 1024 Jul 3 08:41 .ICE-unix
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drwx------ 2 root root 12288 Jul 3 07:47 lost+found
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drwxr-xr-x 3 user1 user1 1024 Jul 5 03:24 opt
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-rw-r--r-- 1 root root 489 Jul 3 10:14 sources.list
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-r--r----- 1 root root 491 Jul 3 10:21 sudoers
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drwxrwxrwt 2 root root 1024 Jul 3 08:41 .X11-unix
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user1@vm1:/tmp$ dd_if=$(mount | grep /tmp | cut -d ' ' -f 1) && echo $dd_if
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/dev/sda8
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user1@vm1:~$ cd && ls -alh
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total 243M
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drwxr-xr-x 3 user1 user1 4.0K Jul 5 04:27 .
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drwxr-xr-x 4 root root 4.0K Jul 3 08:39 ..
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-rw------- 1 user1 user1 22 Jul 3 10:45 .bash_history
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-rw-r--r-- 1 user1 user1 220 Jul 3 08:39 .bash_logout
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-rw-r--r-- 1 user1 user1 3.2K Jul 3 08:39 .bashrc
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-rw------- 1 user1 user1 52 Jul 5 04:12 .lesshst
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drwxr-xr-x 3 user1 user1 4.0K Jul 5 03:23 opt
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-rw-r--r-- 1 user1 user1 675 Jul 3 08:39 .profile
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-rw-r--r-- 1 user1 user1 1.3M Jul 5 04:25 root.tgz
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-rw-r--r-- 1 root root 241M Jul 5 04:36 tmp.img
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user1@vm1:~$ sudo losetup /dev/loop1 ~/tmp.img && sudo mount /dev/loop1 /mnt/
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user1@vm1:~$ ls -al /mnt
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total 19
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drwxrwxrwt 6 root root 1024 Jul 5 04:17 .
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drwxr-xr-x 22 root root 1024 Jul 3 08:29 ..
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drwxrwxrwt 2 root root 1024 Jul 3 08:41 .ICE-unix
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drwx------ 2 root root 12288 Jul 3 07:47 lost+found
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drwxr-xr-x 3 user1 user1 1024 Jul 5 03:24 opt
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-rw-r--r-- 1 root root 489 Jul 3 10:14 sources.list
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-r--r----- 1 root root 491 Jul 3 10:21 sudoers
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drwxrwxrwt 2 root root 1024 Jul 3 08:41 .X11-unix
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user1@vm1:~$ sudo umount /mnt && sudo losetup -d /dev/loop1
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user1@vm1:~$ sudo umount $dd_if && sudo mkfs.ext3 $dd_if
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mke2fs 1.41.12 (17-May-2010)
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Filesystem label=
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OS type: Linux
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Block size=1024 (log=0)
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Fragment size=1024 (log=0)
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Stride=0 blocks, Stripe width=0 blocks
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61752 inodes, 246784 blocks
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12339 blocks (5.00%) reserved for the super user
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First data block=1
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Maximum filesystem blocks=67371008
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31 block groups
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8192 blocks per group, 8192 fragments per group
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1992 inodes per group
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Superblock backups stored on blocks:
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8193, 24577, 40961, 57345, 73729, 204801, 221185
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Writing inode tables: done
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Creating journal (4096 blocks): done
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Writing superblocks and filesystem accounting information: done
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This filesystem will be automatically checked every 27 mounts or
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180 days, whichever comes first. Use tune2fs -c or -i to override.
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user1@vm1:~$ new_uuid=$(sudo tune2fs -l $dd_if | awk '/UUID/{print $3}') && echo $new_uuid
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f8288adc-3ef9-4a6e-aab2-92624276b8ba
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user1@vm1:~$ grep '/tmp' /etc/fstab
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# /tmp was on /dev/sda8 during installation
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UUID=011b4530-e4a9-4d13-926b-48d9e33b64bf /tmp ext3 defaults 0 2
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user1@vm1:~$ sed "s/^UUID=.*\/tmp\s\+ext3\s\+defaults\s\+[0-9]\s\+[0-9]\s\?/UUID=$new_uuid \/tmp ext3 defaults 0 2/" /etc/fstab
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# /etc/fstab: static file system information.
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#
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# Use 'blkid' to print the universally unique identifier for a
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# device; this may be used with UUID= as a more robust way to name devices
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# that works even if disks are added and removed. See fstab(5).
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#
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# <file system> <mount point> <type> <options> <dump> <pass>
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proc /proc proc defaults 0 0
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# / was on /dev/sda1 during installation
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UUID=91aacf33-0b35-474c-9c61-311e04b0bed1 / ext3 errors=remount-ro 0 1
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# /home was on /dev/sda9 during installation
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UUID=e27b0efb-8cf0-439c-9ebe-d59c927dd590 /home ext3 defaults 0 2
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# /tmp was on /dev/sda8 during installation
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UUID=f8288adc-3ef9-4a6e-aab2-92624276b8ba /tmp ext3 defaults 0 2
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# /usr was on /dev/sda5 during installation
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UUID=9f49821b-7f94-4915-b9a9-ed9f12bb6847 /usr ext3 defaults 0 2
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# /var was on /dev/sda6 during installation
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UUID=b7e908a1-a1cd-4d5c-bc79-c3a99d003e7c /var ext3 defaults 0 2
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# swap was on /dev/sda7 during installation
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UUID=292981d7-5a17-488f-8d9a-176b65f45d46 none swap sw 0 0
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/dev/scd0 /media/cdrom0 udf,iso9660 user,noauto 0 0
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sudo sed -i'.bak' "s/^UUID=.*\/tmp\s\+ext3\s\+defaults\s\+[0-9]\s\+[0-9]\s\?/UUID=$new_uuid \/tmp ext3 defaults 0 2/" /etc/fstab
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sudo mount -a && ls /tmp
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user1@vm1:~$ sudo umount /tmp && pv ~/tmp.img | sudo dd of=$dd_if bs=10M
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241MB 0:00:04 [54.2MB/s] [===============================================================================================================>] 100%
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0+1928 records in
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0+1928 records out
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252706816 bytes (253 MB) copied, 5.52494 s, 45.7 MB/s
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user1@vm1:~$ rm -v tmp.img
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rm: remove write-protected regular file `tmp.img'? y
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removed `tmp.img'
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user1@vm1:~$
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```
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## 解释
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1. 在你的主目录中创建归档或`/opt/root/`。归档文件的扩展名是`.tgz`,因为这个归档实际上由两部分组成,就像是俄罗斯套娃。第一部分由字母`t`指定,是一个大文件,其中所有归档文件由程序`tar`合并。第二部分由字母`gz`指定 ,意味着`tar`调用`gzip`程序来压缩它。
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1. 测试这个归档。
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1. 将目录更改为`/tmp`。
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1. 解压你的归档。
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1. 打印目录内容。
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1. 提取挂载在`/tmp`上的分区的名称,将其存储在`dd_if`变量中,如果提取成功,打印出`dd_if`值。`if`代表输入文件。
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1. 将整个分区复制到你的主目录中的`tmp.img`。dd 使用超级用户调用,因为你正在访问代表你的分区的文件`/dev/sda8`,该分区对普通用户不可访问。
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1. 将目录更改为你的主目录并打印出其内容。
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1. 告诉 Linux 将`tmp.img`文件用作(一种)物理分区并挂载它。
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1. 打印出`tmp.img`的内容。你可以看到它真的是`/tmp`的精确副本 。
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1.
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1. 解除挂载`tmp.img`,并告诉 Linux 停止将其看做分区。
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1. 解除挂载`/tmp`并在那里创建新的文件系统,删除该过程中的所有东西。
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1. 提取你的新`/tmp`文件系统的UUID ,将其存储在`new_uuid`中,并打印出来。
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1. 从`/etc/fstab`中打印描述旧的`/tmp`分区的一行。
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1. 向你展示,修改后的`/etc/fstab`如何工作。通过使用正则表达式来完成,这个表达式用作掩码,定义了这一行:
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```
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UUID=f8288adc-3ef9-4a6e-aab2-92624276b8ba /tmp ext3 defaults 0 2
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```
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完成这本书后,我会给你一个链接,让你学习如何创建这样的正则表达式。
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1. 使用新的 UUID 实际替换`/tmp`旧的 UUID。
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1. 挂载`/etc/fstab`中描述的所有文件系统,并列出新`/tmp`的内容
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1. 解除挂载新的`/tmp`并从`tmp.img`恢复旧`/tmp`。
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1. 获取旧`/tmp`的 UUID,它实际上与创建新文件系统之前相同,因为`tmp.img`是旧的`/ tmp`的完美副本。
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1. 在`/etc/fstab`中用旧的 UUID 替换新的 UUID 。
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1. 从`/etc/fstab`挂载所有文件系统。如果此命令不会导致错误,你可能一切正常。恭喜。
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1. 从你的主目录中删除`tmp.img`。
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## 附加题
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+ 尝试详细解释每个命令的作用。拿出一张纸,把它全部写出来。在`man`中查找在所有不能很好理解的命令和参数。
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+ 这个有些过早了,但为什么你能作为`user1`来发出删除命令,从你的主目录中删除`tmp.img`,考虑到`tmp.img`由 root 创建?
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