一,作用

/etc/fstab是用來存放文件系統的靜態信息的文件,當系統啟動時,系統會自動地從這個文件讀取信息,並且會自動將此文件中指定的文件系統掛在到執行的目錄

二,掛載的限制

1,根目錄是必須掛載的,而且一定要先於其他mount point被掛載.因為mount是所有目錄的根目錄,其他目錄都是由根目錄/ 衍生出來的
2,掛載點的指定可以任意,但必須遵守必要的系統目錄架構原則
3,掛載點必須是已經存在的目錄
4,所有掛載點在同一時間只能被掛載一次
5,所有分區在同一時間只能掛在一次
6,若進行卸載,必須將工作目錄退出掛載點(及其子目錄)之外

三,/etc/fstab文件中的參數

cat /etc/fstab 查看當前系統已經存在的掛載信息
[root@server ~]# cat /etc/fstab

#
# /etc/fstab
# Created by anaconda on Fri Mar 24 19:30:39 2017
#
# Accessible filesystems, by reference, are maintained under '/dev/disk'
# See man pages fstab(5), findfs(8), mount(8) and/or blkid(8) for more info
#
UUID=fd93d9dc-e277-4926-8a83-c731b5600f8b / ext4 defaults 1 1
UUID=c9517f8f-081d-444f-8510-92d236671b37 /boot ext4 defaults 1 2
UUID=bd841c60-daf5-4c5d-8392-95d4e8b9f4e7 /opt ext4 defaults 1 2
UUID=fe6dd69c-99f4-478d-acc7-ef7e156e5bc5 /usr/local ext4 defaults 1 2
UUID=1e71b8a2-bb4e-4e39-a894-e04fb6480e2e swap swap defaults 0 0
tmpfs /dev/shm tmpfs defaults 0 0
devpts /dev/pts devpts gid=5,mode=620 0 0
sysfs /sys sysfs defaults 0 0
proc /proc proc defaults 0 0

第一列:Device:磁碟設備文件或者該設備的Label或者UUID

The first field, (fs_spec), describes the block special device or remote filesystem to be mounted.
1),查看分區的label和uuid
Label就是分區的標簽,在最初安裝系統時填寫的掛載點就是標簽的名字.可以通過查看一個分區的superblock中的信息找到UUID和Label Name
如:要查看/dev/sda1這個設備的uuid和label name
命令1:dumpe2fs -h /dev/sda1
[root@server ~]# dumpe2fs -h /dev/sda1
dumpe2fs 1.41.12 (17-May-2010)
Filesystem volume name: <none>
Last mounted on: /boot ---->這個就是Label name
Filesystem UUID: c9517f8f-081d-444f-8510-92d236671b37 ---->UUID
Filesystem magic number: 0xEF53

命令2：blkid
[root@server ~]# blkid
/dev/sda1: UUID="c9517f8f-081d-444f-8510-92d236671b37" TYPE="ext4"
/dev/sda2: UUID="1e71b8a2-bb4e-4e39-a894-e04fb6480e2e" TYPE="swap"
2),使用設備名和label及uuid作為標識的不同
使用設備名稱(/dev/sda)來掛載分區時是被固定死的，一旦磁碟的插槽順序發生了變化，就會出現名稱不對應的問題。因為這個名稱是會改變的。
不過使用label掛載就不用擔心插槽順序方面的問題。不過要隨時註意label name，至於uuid，每個分區被格式化以後就會有一個UUID作為唯一的標識好。使用UUID作為唯一的標識號，使用UUID掛載的話就不用擔心會發生錯亂的問題

第二列： Mount point：設備的掛載點，就是要掛載到哪個目錄下
The second field, (fs_file), describes the mount point for the filesystem. For swap partitions, this field should be specified as ‘none’. If the name of the mount point contains spaces these can be escaped as ‘\040’.

第三列：filesystem：磁碟文件系統的格式，支持許多不同的文件系統：ext2,ext3,ext4,reiserfs,xfs,jfs,smbfs,iso9660,vfat,swap及auto，設置成auto類型，mount命令會猜測使用的文件系統類型，對CDROM和DVD等移動設備是非常有用的

The third field, (fs_vfstype), describes the type of the filesystem. Linux supports lots of filesystem types, such as adfs,affs, autofs, coda, coherent, cramfs, devpts, efs, ext2, ext3, hfs, hpfs, iso9660, jfs, minix, msdos, ncpfs, nfs, ntfs, proc,qnx4, reiserfs, romfs, smbfs, sysv, tmpfs, udf, ufs, umsdos, vfat, xenix, xfs, and possibly others. For more details, see mount(8). For the filesystems currently supported by the running kernel, see /proc/filesystems. An entry swap denotes a file or partition to be used for swapping, cf. swapon(8). An entry ignore causes the line to be ignored. This is useful to show disk partitions which are currently unused. An entry none is useful for bind or move mounts.

第四列：parameters：文件系統的參數

 The fourth field, (fs_mntops), describes the mount options associated with the filesystem.

第五列：能否被dump備份命令作用：dump是一個用來作為備份的命令，通常這個參數的值為0或1

  The fifth field, (fs_freq), is used for these filesystems by the dump(8) command to determine which filesystems need to be dumped. If the fifth field is not present, a value of zero is returned and dump will assume that the filesystem does not need to be dumped.

第六列：是否檢驗扇區：開機的過程中，系統預設會以fsck檢驗我們系統是否為完整（clean）

   The sixth field, (fs_passno), is used by the fsck(8) program to determine the order in which filesystem checks are done at reboot time. The root filesystem should be specified with a fs_passno of 1, and other filesystems should have a fs_passno of 2. Filesystems within a drive will be checked sequentially, but filesystems on different drives will be checked at the same time to utilize parallelism available in the hardware. If the sixth field is not present or zero, a value of zero is returned and fsck will assume that the filesystem does not need to be checked.