Linux /etc/fstab文件，linuxetcfstab文件

Linux /etc/fstab文件，linuxetcfstab文件

一,作用

/etc/fstab是用来存放文件系统的静态信息的文件,当系统启动时,系统会自动地从这个文件读取信息,并且会自动将此文件中指定的文件系统挂在到执行的目录

二,挂载的限制

1,根目录是必须挂载的,而且一定要先于其他mount point被挂载.因为mount是所有目录的根目录,其他目录都是由根目录/ 衍生出来的
2,挂载点的指定可以任意,但必须遵守必要的系统目录架构原则
3,挂载点必须是已经存在的目录
4,所有挂载点在同一时间只能被挂载一次
5,所有分区在同一时间只能挂在一次
6,若进行卸载,必须将工作目录退出挂载点(及其子目录)之外

三,/etc/fstab文件中的参数

cat /etc/fstab 查看当前系统已经存在的挂载信息
[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:磁盘设备文件或者该设备的Label或者UUID

The first field, (fs_spec), describes the block special device or remote filesystem to be mounted.
1),查看分区的label和uuid
Label就是分区的标签,在最初安装系统时填写的挂载点就是标签的名字.可以通过查看一个分区的superblock中的信息找到UUID和Label Name
如:要查看/dev/sda1这个设备的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 ---->这个就是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),使用设备名和label及uuid作为标识的不同
使用设备名称(/dev/sda)来挂载分区时是被固定死的，一旦磁盘的插槽顺序发生了变化，就会出现名称不对应的问题。因为这个名称是会改变的。
不过使用label挂载就不用担心插槽顺序方面的问题。不过要随时注意label name，至于uuid，每个分区被格式化以后就会有一个UUID作为唯一的标识好。使用UUID作为唯一的标识号，使用UUID挂载的话就不用担心会发生错乱的问题

第二列： Mount point：设备的挂载点，就是要挂载到哪个目录下
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：磁盘文件系统的格式，支持许多不同的文件系统：ext2,ext3,ext4,reiserfs,xfs,jfs,smbfs,iso9660,vfat,swap及auto，设置成auto类型，mount命令会猜测使用的文件系统类型，对CDROM和DVD等移动设备是非常有用的

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：文件系统的参数

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

第五列：能否被dump备份命令作用：dump是一个用来作为备份的命令，通常这个参数的值为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：是否检验扇区：开机的过程中，系统默认会以fsck检验我们系统是否为完整（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.