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fstab is a configuration file that contains information of all the partitions and storage devices in your computer. The file is
located under /etc, so the full path to this file is /etc/fstab.
/etc/fstab contains information of where your partitions and storage devices should be mounted and how. If you can't
access your Windows partition from Linux, aren't able to mount your CD or write to your floppy as a normal user, or have
problems with your CD-RW, you probably have a misconfigured /etc/fstab file. So, you can usually fix your mounting
problems by editing your fstab file.
/etc/fstab is just a plain text file, so you can open and edit it with any text editor you're familiar with. However, note
that you must have the root privileges before editing fstab. So, in order to edit the file, you must either log in as root or
use the su command to become root.
< Overview of the file >
Of course everybody has a bit different /etc/fstab file because the partitions, devices and their properties are different
on different systems. But the basic structure of fstab is always the same. Here's an example of the contents of
/etc/fstab:
/dev/hda2 / ext2 defaults 11
/dev/hdb1 /home ext2 defaults 12
/dev/cdrom /media/cdrom auto ro,noauto,user,exec 00
/dev/fd0 /media/floppy auto rw,noauto,user,sync 00
proc /proc proc defaults 00
/dev/hda1 swap swap pri=42 00
What does all this gibberish mean? As you see, every line (or row) contains the information of one device or partition. The
first column contains the device name, the second one its mount point, third its filesystem type, fourth the mount options,
fifth (a number) dump options, and sixth (another number) filesystem check options. Let's take a closer look at this stuff.
< 1st and 2nd columns: Device and default mount point >
The first and second columns should be pretty straightforward. They tell the mount command exactly the same things that
you tell mount when you mount stuff manually: what is the device or partition, and what is the mount point. The mount
point specified for a device in /etc/fstab is its default mount point. That is the directory where the device will be
mounted if you don't specify any other mount point when mounting the device.
Like you already learned from the Mounting tuXfile, most Linux distros create special directories for mount points. Most
distros create them under /mnt, but some (at least SuSE) under /media. As you probably noticed when looking at the
example fstab, I use SuSE's mount points as an example.
What does all this mean? If I type the following command:
$ mount /dev/fd0
... my floppy will be mounted in /media/floppy, because that's the default mount point specified in /etc/fstab. If
there is no entry for /dev/fd0 in my fstab when I issue the command above, mount gets very confused because it
doesn't know where to mount the floppy.
You can freely change the default mount points listed in /etc/fstab if you're not satisfied with the defaults your distro
has given you. Just make sure the mount point is a directory that already exists on your system. If it doesn't, simply create it.
Some partitions and devices are also automatically mounted when your Linux system boots up. For example, have a look at
the example fstab above. There are lines that look like this:
/dev/hda2 / ext2 defaults 1 1
/dev/hdb1 /home ext2 defaults 1 2
As you've learned, these lines mean that /dev/hda2 will be mounted to / and /dev/hdb1 to /home. This is done
automatically when your Linux system boots up... if it wouldn't, you'd have a hard time using your cool Linux system
because all the programs you use are in / and you wouldn't be able to run them if / wasn't mounted! But how does the
system know where you want to mount /dev/hda2 and /dev/hdb1? By looking at the /etc/fstab file of course.
< 3rd column: Filesystem type >
The third column in /etc/fstab specifies the filesystem type of the device or partition. Many different filesystems are
supported but we'll take a look at the most common ones only.
ext2 and ext3 Very likely your Linux partitions are Ext3. Ext2 used to be the standard filesystem for Linux, but these days,
Ext3 and ReiserFS are usually the default filesystems for almost every new Linux distro. Ext3 is a newer filesystem type
that differs from Ext2 in that it's journaled, meaning that if you turn the computer off without properly shutting down, you
shouldn't lose any data and your system shouldn't spend ages doing filesystem checks the next time you boot up.
reiserfs Your Linux partitions may very well be formatted as ReiserFS. Like Ext3, ReiserFS is a journaled filesystem, but
it's much more advanced than Ext3. Many Linux distros (including SuSE) have started using ReiserFS as their default
filesystem for Linux partitions.
swap The filesystem name is self-explanatory. The filesystem type "swap" is used in your swap partitions.
vfat and ntfs Your Windows partitions are probably either Vfat or NTFS. The 9x series (95, 98, ME) all use Vfat (more
widely known as FAT32), and the NT series (NT, 2000, XP) use NTFS. In 2000 and XP you can choose the filesystem type,
so 2000 and XP partitions may be formatted as Vfat, too. If you want to be able to write to your Windows partitions from
Linux, I suggest formatting them as Vfat, because Linux's support for writing to NTFS partitions is a bit shabby at this
moment.
auto No, this isn't a filesystem type :-) The option "auto" simply means that the filesystem type is detected automatically. If
you take a look at the example fstab above, you'll see that the floppy and CD-ROM both have "auto" as their filesystem
type. Why? Their filesystem type may vary. One floppy might be formatted for Windows and the other for Linux's Ext2.
That's why it's wise to let the system automatically detect the filesystem type of media such as floppies and cdroms.
< 4th column: Mount options >
The fourth column in fstab lists all the mount options for the device or partition. This is also the most confusing column
in the fstab file, but knowing what some of the most common options mean, saves you from a big headache. Yes, there
are many options available, but I'll take a look at the most widely used ones only. For more information, check out the man
page of mount.
auto and noauto With the auto option, the device will be mounted automatically (at bootup, just like I told you a bit
earlier, or when you issue the mount -a command). auto is the default option. If you don't want the device to be
mounted automatically, use the noauto option in /etc/fstab. With noauto, the device can be mounted only
explicitly.
user and nouser These are very useful options. The user option allows normal users to mount the device, whereas
nouser lets only the root to mount the device. nouser is the default, which is a major cause of headache for new Linux
users. If you're not able to mount your cdrom, floppy, Windows partition, or something else as a normal user, add the user
option into /etc/fstab.
exec and noexec exec lets you execute binaries that are on that partition, whereas noexec doesn't let you do that.
noexec might be useful for a partition that contains binaries you don't want to execute on your system, or that can't even
be executed on your system. This might be the case of a Windows partition.
exec is the default option, which is a good thing. Imagine what would happen if you accidentally used the noexec option
with your Linux root partition...
ro Mount the filesystem read-only.
rw Mount the filesystem read-write. Again, using this option might cure the headache of many new Linux users who are
tearing their hair off because they can't write to their floppies, Windows partitions, or something else.
sync and async How the input and output to the filesystem should be done. sync means it's done synchronously. If you
look at the example fstab, you'll notice that this is the option used with the floppy. In plain English, this means that when
you, for example, copy a file to the floppy, the changes are physically written to the floppy at the same time you issue the
copy command.
However, if you have the async option in /etc/fstab, input and output is done asynchronously. Now when you copy a
file to the floppy, the changes may be physically written to it long time after issuing the command. This isn't bad, and may
sometimes be favorable, but can cause some nasty accidents: if you just remove the floppy without unmounting it first, the
copied file may not physically exist on the floppy yet!
async is the default. However, it may be wise to use sync with the floppy, especially if you're used to the way it's done in
Windows and have a tendency to remove floppies before unmounting them first.
defaults Uses the default options that are rw, suid, dev, exec, auto, nouser, and async.
< 5th and 6th columns: Dump and fsck options >
Dump and, uh, what options? Well, dump is a backup utility and fsck is a filesystem check utility. I won't discuss them in
great length here (they would both need their own tuXfile), but I'll mention them, because otherwise you'd spend the rest of
the day wondering what on God's green Earth do these things mean.
The 5th column in /etc/fstab is the dump option. Dump checks it and uses the number to decide if a filesystem should
be backed up. If it's zero, dump will ignore that filesystem. If you take a look at the example fstab, you'll notice that the
5th column is zero in most cases.
The 6th column is a fsck option. fsck looks at the number in the 6th column to determine in which order the filesystems
should be checked. If it's zero, fsck won't check the filesystem.
< Example /etc/fstab entries >
As an example, we'll take a look at a couple of fstab entries that have been a source of endless frustration for new Linux
users: floppy and CD-ROM (although these days floppies aren't that important anymore).
/dev/fd0 /media/floppy auto rw,noauto,user,sync 0 0
This line means that the floppy is mounted to /media/floppy by default and that its filesystem type is detected
automatically. This is useful because the type of the floppy may wary. Note especially the rw and user options: they must
be there if you want to be able to mount and write to the floppy as a normal user. If you have trouble with this, check your
fstab file to see if these options are there. Also note the sync option. It can be async just as well, but it's sync because of
reasons discussed a bit earlier.
/dev/cdrom /media/cdrom auto ro,noauto,user,exec 0 0
Note, again, the user option that enables you to mount the CD as a normal user. The CD-ROM has the ro option because it's
no use mounting a CD-ROM read-write because you wouldn't be able to write to it anyway. Also note the exec option. It's
especially useful if you'd like to be able to execute something from your CD.
Also note that the noauto option is used with the floppy and CD-ROM. This means that they won't be automatically
mounted when your Linux system boots up. This is useful for removable media, because sometimes there won't be any
floppy or CD-ROM when you boot up your system, so there isn't any reason to try to mount something that doesn't even
exist.
موضوع: کسی میتونه توضیحات کاملی در مورد fstabبده؟ (دفعات بازدید: 2645 بار)
