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Mounting File Systems Automatically: /etc/fstab

next section. Although you can mount a file system directly with only a

mount command, you can simplify the process by placing mount information in the /etc/fstab configuration file. Using entries in this file, you can have certain file systems automatically mounted whenever your system boots. For others, you can specify configuration information, such as mountpoints and access permissions, which can be automatically used whenever you mount a file system. You needn't enter this information as arguments to a

mount command as you otherwise must. This feature is what allows mount utilities on GNOME or KDE to enable you to mount a file system simply by clicking a window icon. All the mount information is already in the /etc/fstab file. For example, when you add a new hard disk partition to your Linux system, you most likely want to have it automatically mounted on startup, and then unmounted when you shut down. Otherwise, you must mount and unmount the partition explicitly each time you boot up and shut down your system. To have Linux automatically mount the file system on your new hard disk partition, you only need to add its name to the fstab file. You can do this by directly and carefully editing the /etc/fstab file to type in a new entry.

An entry in an fstab file contains several fields, each separated from the next by a space or tab. These are described as the device, mountpoint, file system type, options, dump, and

fsck fields, arranged in the sequence shown here:

<device> <mountpoint> <filesystemtype> <options> <dump> <fsck>

The first field is the name of the file system to be mounted. This entry can be either a device name or an ext2 or ext3 file system label. A device name usually begins with /dev, such as /dev/hda3 for the third hard disk partition. A label is specified by assigning the label name to the tag

LABEL , as in

LABEL=/ for an ext2 root partition. The next field is the directory in your file structure where you want the file system on this device to be attached. These are empty directories to be used for file systems, such as /dev/floppy. The third field is the type of file system being mounted. Table 30-7 provides a list of all the different types you can mount. The type for a standard Linux hard disk partition is ext3. The next example shows an entry for the main Linux hard disk partition. This entry is mounted at the root directory, /, and has a file type of ext3:

/dev/hda3    /     ext3    defaults   0   1

The following example shows a

LABEL entry for the hard disk partition, where the label name is /:

LABEL=/     /      ext3   defaults   0   1

Auto Mounts

The file system type for a floppy may differ depending on the disk you are trying to mount. For example, you may want to read a Windows-formatted floppy disk at one time and a Linux-formatted floppy disk at another time. For this reason, the file system type specified for the floppy device is

auto . With this option, the type of file system formatted on the floppy disk is detected automatically, and the appropriate file system type is used.

/dev/fd0  /mnt/floppy  auto   defaults,noauto   0 0

mount Options

The field after the file system type lists the different options for mounting the file system. You can specify a default set of options by simply entering

defaults , or you can list specific options next to each other separated by a comma (no spaces). The

defaults option specifies that a device is read/write (

rw ), that it is asynchronous (

async ), that it is a block device (

dev ), that it cannot be mounted by ordinary users (

nouser ), and that programs can be executed on it (

exec ). By contrast, a CD-ROM has only two options listed for it:

ro and

noauto .

ro specifies that the device is read-only, and

noauto specifies it is not automatically mounted. The

noauto option is used with both CD-ROMs and floppy drives, so they won't automatically mount, because you don't know if you have anything in them when you start up. At the same time, the entries for both the CD-ROM and the floppy drive specify where they are to be mounted when you decide to mount them. On Red Hat, the

kudzu option invokes the Red Hat Kudzu tool, which checks to see if the device has been installed on your system, and that the kernel is running the appropriate drivers for that CD-ROM or floppy disk. Table 30-8 lists the options for mounting a file system. An example of CD-ROM and floppy drive entries follows. Notice the type for a CD-ROM file system is different from that for a hard disk partition,

iso9660 .

/dev/hdc   /mnt/cdrom    iso9660  noauto,owner,kudzu,ro 0  0
/dev/fd0   /mnt/floppy   auto     noauto,owner,kudzu    0  0

Boot and Disk Check

The last two fields of an

fstab entry consist of integer values. The first one is used by the

dump command to determine if a file system needs to be dumped, backing up the file system. The second value is used by

fsck to see if a file system should be checked at reboot, and in what order with other file systems. If the field has a value of 1, it indicates a boot partition, and 2 indicates other partitions. The 0 value means

fsck needn't check the file system.

A copy of an /etc/fstab file is shown here. Notice the first line is a comment. All comment lines begin with a

# . The entry for the /proc file system is a special entry used by your Linux operating system for managing its processes; it is not an actual device. To make an entry in the /etc/fstab file, you can edit the /etc/fstab file directly. You can use the example /etc/fstab file shown here as a guide to show how your entries should look. The

/proc and

swap partition entries are particularly critical.

/etc/fstab

# <device> <mountpoint> <filesystemtype> <options>            <dump><fsck>
/dev/hda3      /              ext3          defaults                 0    1
none           /proc          proc          defaults                 0    0
none           /dev/pts       devpts        gid=5,mode=620           0    0
none           /dev/shm       tmpfs         defaults                 0    0
/dev/hda2      swap           swap          defaults                 0    0
/dev/hdc       /mnt/cdrom     iso9660       noauto,owner,kudzu,ro    0    0
/dev/fd0       /mnt/floppy    auto          noauto,owner,kudzu       0    0
/dev/hda1      /mnt/windows   vfat          defaults                 0    0

CD-ROM and Floppy Defaults

Red Hat creates entries in the fstab file for any CD-ROM and floppy devices you may have. It also creates directories where these drives can be mounted. For Red Hat, these are /mnt/cdrom for your CD-ROM and /mnt/floppy for your floppy disk. If you have several CD-ROMs or floppy drives, directories are created for them with sequential numbers. So on Red Hat, a second CD-ROM drive will use a directory named /mnt/cdrom1.

Partition Labels: e2label

Red Hat uses file system labels for ext2 and ext3 file systems on hard disk partitions. Thus in the /etc/fstab file previously shown, the first entry would use a label for its device name, as shown here. In this case, the label is the slash, /, indicating the root partition. You could change this device's label with

e2label , but be sure to also change the

/etc/fstab entry for it.

LABEL=/     /     ext3   defaults    0   1

For ext2 and ext3 partitions, you can change or add a label with the

e2label tool or

tune2fs with the

-L option. Specify the device and the label name. If you change a label, be sure to change corresponding entries in the /etc/fstab file. Just use

e2label with the device name to find out what the current label is. In the next example, the user changes the label of the /dev/hda3 device to

TURTLE :

e2label /dev/hda3  TURTLE

Windows Partitions

You can mount either MS-DOS, Windows 95/98/ME, or Windows XP, NT, and 2000 partitions used by your Windows operating system onto your Linux file structure, just as you would mount any Linux file system. You have to specify the file type of

vfat for Windows 95/98/ME, and

msdos for MS-DOS. Windows XP, NT, and 2000 use the

ntfs file type. You may find it convenient to have your Windows partitions automatically mounted when you start up your Linux system. To do this, you need to put an entry for your Windows partitions in your /etc/fstab file and give it the

defaults option, or be sure to include an

auto option. You make an entry for each Windows partition you want to mount, and then specify the device name for that partition, followed by the directory in which you want to mount it. The /mnt/windows directory would be a logical choice (be sure the windows directory has already been created in /mnt). The next example shows a standard Windows partition entry for an /etc/fstab file. Notice the last entry in the /etc/fstab file example is an entry for mounting a Windows partition.

/dev/hda1 /mnt/windows vfat defaults 0 0

Linux Kernel Interfaces

Your /etc/fstab file may also have entries for two special kernel interface file systems,

devpts and

tmpfs . Both provide kernel interfaces that are not supported by standard devices. The

/dev/pts entry mounts a

devpts file system for pseudo-terminals. The

/dev/shm entry mounts the

tmpfs file system (also known as

shmfs ) to implement Linux Virtual Memory, POSIX shared memory maintenance access. This is designed to overcome the 4GB memory limitation on current systems, extending usable memory to 64GB.

If your /etc/fstab file ever becomes corrupt—say, if a line gets deleted accidentally or changed—your system will boot into a maintenance mode, giving you read-only access to your partitions. To gain read/write access so that you can fix your /etc/fstab file, you have to remount your main partition. The following command performs such an operation:

# mount -n -o remount,rw /

noauto

File systems listed in the /etc/fstab file are automatically mounted whenever you boot, unless this feature is explicitly turned off with the

noauto option. Notice that the CD-ROM and floppy disks in the sample fstab file earlier in this chapter have a

noauto option. Also, if you issue a

mount

-a command, all the file systems without a

noauto option are mounted. If you want to make the CD-ROM user-mountable, add the

user option.

/dev/hdc /mnt/cdrom iso9660 ro,noauto,user 0 0