Книга: Fedora™ Unleashed, 2008 edition

Mounting Automatically with /etc/fstab

Mounting Automatically with /etc/fstab

A special file, /etc/fstab, exists to provide the system with predetermined options and mount points so that the file systems can be automatically or manually mounted with minimal typing and without having to recall arcane Linux syntax.

The /etc/fstab file can only be written to by the super-user. The commands fsck, mount, and umount all read information from /etc/fstab. Each file system gets its own line with the information separated by tabs.

On each line of fstab, the first field indicates the block device or remote file system that will be mounted. The second field identifies the mount point on the local system where the file system will be mounted. The third field is the file system type, and the fourth field is a comma-delimited list of mount options. Options include:

? exec — If this option is specified, binaries can be executed from this file system.

? noauto — This means that the -a option does not cause the file system to be mounted and it is not mounted at bootup.

? noexec — If this option is specified, binaries cannot be executed from this file system.

? nosuid — This option does not permit set-user-identifier or set-group- identifier bits to take effect.

? ro — This option mounts the file system as read-only.

? rw — This option mounts the file system as read/write.

? sync — Reading from and writing to the files are done synchronously.

? user — This option allows a regular (not just root) user to mount the file system, but it includes the options noexec, nosuid, and nodev by default unless they are overridden by exec, dev, and suid.

For iso9660 file systems, the interesting option is unhide, which shows hidden and associated files.

The fstab man pages contain an in-depth description of fstab and its options.

The fifth field of /etc/fstab is used by dump (a traditional Unix backup program) to determine whether the file system should be dumped (backed up); 1 is yes, and 0 is no. Default values are set for you during the initial installation. They are of concern only if you actually use dump; then you would set the value to 1 for the file systems you wanted to back up.

The sixth field is used by fsck to determine how fsck needs to interact with the file system — 0 means that fsck is never run on the file system (a FAT32 file system, for example); 1 means that fsck will be run on the drive at a predetermined time. 2 is recommended for nonroot file systems so that fsck is not run on them as frequently.

Here is a simple /etc/fstab file from a system with a RAID0 ext3 root partition and dual-booted with MS Windows:

LABEL=/12  /           ext3    defaults              1 1
none       /dev/pts    devpts  gid=5,mode=620        0 0
none       /proc       proc    defaults              0 0
none       /dev/shm    tmpfs   defaults              0 0
/dev/hda11 swap        swap    defaults              0 0
/dev/cdrom /mnt/cdrom  iso9660 noauto,owner,kudzu,ro 0 0
/dev/fd0   /mnt/floppy auto    noauto,owner,kudzu    0 0
/dev/hda1  /mnt/win_c  vfat    auto,quiet,exec       0 0

Notice the two entries marked with the kudzu option. This is the result of the actions of updfstab, which keeps fstab synchronized with the state of any removable devices on the system such as CD-ROMs. The quiet option shown for the Windows partition suppresses error messages and is recommended if you use the Wine application.

As mentioned earlier, you record mounting preferences in /etc/fstab during installation. You need to modify /etc/fstab only if you make changes to your mounts or desire to change the default settings to address the specific needs of your system.

As long as the super-user understands the syntax and options of the fstab file, she can edit the file with any text editor.

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