ex19
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wizardforcel
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# 练习 19：文件系统：挂载，`mount`，`/etc/fstab`
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> 原文：[Exercise 19. Filesystems: mounting, mount, /etc/fstab](https://archive.fo/9OnRm)
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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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我希望你熟悉分区的概念。如果没有，我会简要介绍一下。首先引用自维基百科：
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> 磁盘分区是一种行为，将硬盘驱动器分为多个逻辑存储单元，它们被称为分区，来将一个物理磁盘驱动器视为多个磁盘。
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看一看：
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```
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user1@vm1:~$ sudo parted /dev/vda
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GNU Parted 2.3
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Using /dev/vda
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Welcome to GNU Parted! Type 'help' to view a list of commands.
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(parted) unit GB
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(parted) p
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Model: Virtio Block Device (virtblk)
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Disk /dev/vda: 17.2GB
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Sector size (logical/physical): 512B/512B
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Partition Table: msdos
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Number Start End Size Type File system Flags
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1 0.00GB 13.3GB 13.3GB extended
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5 0.00GB 1.02GB 1.02GB logical ext3 boot
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6 1.03GB 2.05GB 1.02GB logical linux-swap(v1)
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7 2.05GB 3.07GB 1.02GB logical ext3
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8 3.07GB 5.12GB 2.05GB logical ext3
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9 5.12GB 9.22GB 4.09GB logical ext3
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10 9.22GB 13.3GB 4.09GB logical ext3
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(parted)
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```
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这是一个物理硬盘，分为 7 个不同的分区。这样做的原因很多，但最好被理解为“分治”原则的应用。以这种方式分割时，流氓程序不能通过占用所有磁盘空间，使整个服务器崩溃，该程序将限制在其分区中。我不会再谈论磁盘分区，但是我会继续关注文件系统，再次引用[维基百科](http://en.wikipedia.org/wiki/File_system)：
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> 文件系统是一种组织数据的手段。通过提供存储，检索和更新数据的过程，以及管理包含它的设备上的可用空间，数据预期在程序终止后保留。文件系统以有效的方式组织数据，并根据设备的特定特性进行调整。在操作系统和文件系统之间，通常存在紧耦合。一些文件系统提供了机制来控制数据和元数据的访问。确保可靠性是文件系统的主要职责。一些文件系统允许多个程序几乎同时更新同一个文件。
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> 类 Unix 操作系统创建一个虚拟文件系统，这使得所有设备上的所有文件似乎都存在于单个层次结构中。这意味着，在这些系统中，有一个根目录，系统上存在的每个文件位于它下方的某个地方。类 Unix 系统可以使用 RAM 磁盘或网络共享资源作为其根目录。
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这意味着，所有文件系统都集成在一个大树中。对于熟悉 Microsoft Windows 的人来说，这意味着比起`C:\`和`D:\`等盘符，这种命名方案有一个单独的根，`/`，所有其他分区都连接到它上面。将文件系统连接到现有目录的过程称为挂载。连接文件系统的目录称为挂载点。同样，看一看：
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```
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user1@vm1:~$ mount
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/dev/vda5 on / type ext3 (rw,errors=remount-ro)
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tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
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proc on /proc type proc (rw,noexec,nosuid,nodev)
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sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
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udev on /dev type tmpfs (rw,mode=0755)
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tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
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devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620)
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/dev/vda10 on /home type ext3 (rw)
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/dev/vda7 on /tmp type ext3 (rw)
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/dev/vda9 on /usr type ext3 (rw)
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/dev/vda8 on /var type ext3 (rw)
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```
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这是我之前展示给你的相同分区，你可以在这个列表中看到挂载点。不以`/dev/vda`开头的是虚拟文件系统，它允许访问不同的系统设施，但它们和此练习无关。现在我们来看看`/etc/fstab`文件：
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```
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user1@vm1:~$ cat /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/vda5 during installation
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UUID=128559db-a2e0-4983-91ad-d4f43f27da49 / ext3 errors=remount-ro 0 1
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# /home was on /dev/vda10 during installation
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UUID=32852d29-ddee-4a8d-9b1e-f46569a6b897 /home ext3 defaults 0 2
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# /tmp was on /dev/vda7 during installation
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UUID=869db6b4-aea0-4a25-8bd2-f0b53dd7a88e /tmp ext3 defaults 0 2
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# /usr was on /dev/vda9 during installation
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UUID=0221be16-496b-4277-b131-2371ce097b44 /usr ext3 defaults 0 2
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# /var was on /dev/vda8 during installation
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UUID=2db00f94-3605-4229-8813-0ee23ad8634e /var ext3 defaults 0 2
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# swap was on /dev/vda6 during installation
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UUID=3a936af2-2c04-466d-b98d-09eacc5d104c none swap sw 0 0
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/dev/scd0 /media/cdrom0 udf,iso9660 user,noauto 0 0
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```
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看起来很恐怖，但让我们选取一行：
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```
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# <file system> <mount point> <type> <options> <dump> <pass>
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UUID=128559db-a2e0-4983-91ad-d4f43f27da49 / ext3 errors=remount-ro 0 1
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```
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按照字段将其拆开。
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```
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UUID=128559db-a2e0-4983-91ad-d4f43f27da49 # Filesystem to mount. This UUID is synonim for /dev/vda5
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/ # This is root filesystem, mount it to /
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ext3 # This is ext3 filesystem. There are many different filesystems out there
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errors=remount-ro # If any errors encountered during mounting filesystem should be remounted read-only
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0 # This filesystem should not be backed up by dump utility
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1 # This filesystem should be checked first by fsck utility
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```
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和之前一样，这些信息可以通过`man fstab`提供给你。现在我将向你展示使用现有文件系统的几个命令：
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+ `mount` - 打印出所有已挂载的文件系统。
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+ `mount -a` - 挂载`/etc/fstab`中描述的所有文件系统。
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+ `mount /dev/sda<N> /<mount point>` - 挂载分区。
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+ `umount /dev/sda<N> /<mount point>` - 解除挂载分区。
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+ `mount -h` - 打印出使用`mount`的简短帮助。
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+ `fsck` - 检查分区是否有错误。
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+ `blkid` - 打印出唯一的分区标识符。
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现在，你将学习如何列出已安装的分区，挂载和解除挂载它们。
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## 这样做
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```
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1: cat /etc/fstab
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2: mount
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3: sudo blkid
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4: sudo umount /tmp
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5: mount
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6: sudo fsck /tmp
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7: sudo mount -a
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8: mount
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```
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## 你会看到什么
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```
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user1@vm1:~$ cat /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=05d469bb-dbfe-4d5a-9bb2-9c0fe9fa8577 / ext3 errors=remount-ro 0 1
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# /home was on /dev/sda9 during installation
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UUID=a1b936a0-df38-4bf5-b095-6220ffdfc63c /home ext3 defaults 0 2
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# /tmp was on /dev/sda8 during installation
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UUID=d0a86453-0dbb-4f33-a023-6c09fe9fa202 /tmp ext3 defaults 0 2
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# /usr was on /dev/sda5 during installation
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UUID=b9544cbb-cdb6-4f3b-89e7-a339f52bfac7 /usr ext3 defaults 0 2
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# /var was on /dev/sda6 during installation
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UUID=e15e713b-5850-4bc3-b99e-ab6f1d037caa /var ext3 defaults 0 2
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# swap was on /dev/sda7 during installation
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UUID=4d516f09-80ff-4956-8a75-e9757697f6b1 none swap sw 0 0
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/dev/scd0 /media/cdrom0 udf,iso9660 user,noauto 0 0
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user1@vm1:~$ mount
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/dev/sda1 on / type ext3 (rw,errors=remount-ro)
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tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
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proc on /proc type proc (rw,noexec,nosuid,nodev)
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sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
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udev on /dev type tmpfs (rw,mode=0755)
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tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
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devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620)
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/dev/sda9 on /home type ext3 (rw)
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/dev/sda5 on /usr type ext3 (rw)
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/dev/sda6 on /var type ext3 (rw)
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/dev/sda8 on /tmp type ext3 (rw)
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/dev/sda8 on /tmp type ext3 (rw)
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user1@vm1:~$ sudo blkid
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/dev/sda1: UUID="05d469bb-dbfe-4d5a-9bb2-9c0fe9fa8577" TYPE="ext3"
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/dev/sda5: UUID="b9544cbb-cdb6-4f3b-89e7-a339f52bfac7" TYPE="ext3"
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/dev/sda6: UUID="e15e713b-5850-4bc3-b99e-ab6f1d037caa" TYPE="ext3"
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/dev/sda7: UUID="4d516f09-80ff-4956-8a75-e9757697f6b1" TYPE="swap"
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/dev/sda8: UUID="d0a86453-0dbb-4f33-a023-6c09fe9fa202" TYPE="ext3"
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/dev/sda9: UUID="a1b936a0-df38-4bf5-b095-6220ffdfc63c" TYPE="ext3"
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user1@vm1:~$ sudo umount /tmp
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user1@vm1:~$ mount
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/dev/sda1 on / type ext3 (rw,errors=remount-ro)
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tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
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proc on /proc type proc (rw,noexec,nosuid,nodev)
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sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
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udev on /dev type tmpfs (rw,mode=0755)
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tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
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devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620)
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/dev/sda9 on /home type ext3 (rw)
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/dev/sda5 on /usr type ext3 (rw)
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/dev/sda6 on /var type ext3 (rw)
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user1@vm1:~$ sudo fsck /tmp
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fsck from util-linux-ng 2.17.2
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e2fsck 1.41.12 (17-May-2010)
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/dev/sda8: clean, 11/61752 files, 13973/246784 blocks
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user1@vm1:~$ sudo mount -a
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user1@vm1:~$ mount
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/dev/sda1 on / type ext3 (rw,errors=remount-ro)
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tmpfs on /lib/init/rw type tmpfs (rw,nosuid,mode=0755)
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proc on /proc type proc (rw,noexec,nosuid,nodev)
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sysfs on /sys type sysfs (rw,noexec,nosuid,nodev)
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udev on /dev type tmpfs (rw,mode=0755)
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tmpfs on /dev/shm type tmpfs (rw,nosuid,nodev)
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devpts on /dev/pts type devpts (rw,noexec,nosuid,gid=5,mode=620)
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/dev/sda9 on /home type ext3 (rw)
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/dev/sda5 on /usr type ext3 (rw)
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/dev/sda6 on /var type ext3 (rw)
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/dev/sda8 on /tmp type ext3 (rw)
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user1@vm1:~$
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```
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## 解释
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1. 打印你的`/etc/fstab`文件的内容，它包含分区信息以及挂载位置。
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1. 打印当前已挂载的分区。
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1. 打印系统中所有分区的 UUID。
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1. 解除挂载`/tmp`分区，以便你可以检查它。
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1. 再次打印出当前已挂载的分区。`/tmp`现在不存在于此列表中。
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1. 检查`/tmp`分区是否有错误。`fsck`通过读取相应的`/etc/fstab`条目知道要检查哪个分区。
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1. 挂载`/etc/fstab`中描述的所有分区。
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1. 再次打印当前已挂载的分区。`/tmp`已经返回了此列表。
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## 附加题
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+ 阅读`man fstab`, `man mount`。
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+ 阅读 <http://tldp.org/LDP/sag/html/filesystems.html>。
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