Mount

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Revision as of 08:24, 7 May 2008

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The mount command is used to link a file system to the local host allowing access to files stored upon them. These file systems could be on physical media, such as a hard drive, CD-ROM or USB memory key, or virtual media, such as file server shares. FreeBSD has support for reading from a large number of file systems and can write back to a majority of them.

Operation

The mounting of a file system to the local host works by creating a mount-point at which the file system can be accessed. This fits in with the Unix concept of 'everything is a file' and as such a CD-ROM drive, for example, is typically mounted as '/cdrom'. Other file systems are typically mounted under the '/mnt' directory. The technical term is called 'grafting' a device to the local file system tree.

An typical installation of FreeBSD might have the following mount-points:

/       - file system root;
/var    - log files;
/usr    - user specific directories, ports, etc.;
/tmp    - temporary workspace;
/cdrom  - physical CD-ROM drive.

These mount-points are automatically mounted when the system is started because they are stored in a file called '/etc/fstab' (derived from File System TABle). The fstab file used to mount the above listed mount-points contains the following entires:

# Device                Mountpoint      FStype  Options         Dump    Pass#
/dev/ad0s1b             none            swap    sw              0       0
/dev/ad0s1a             /               ufs     rw              1       1
/dev/ad0s1e             /tmp            ufs     rw              2       2
/dev/ad0s1f             /usr            ufs     rw              2       2
/dev/ad0s1d             /var            ufs     rw              2       2
/dev/acd0               /cdrom          cd9660  ro,noauto       0       0

The mounted file systems in this example are physical devices attached to the local system and located under the /dev directory with the hard drive being 'ad0s1x' and CD-ROM being 'acd0'. The 'none' mount-point simply exists to inform the system of where the swap-file (often called 'virtual memory') is located. Further details of the fstab file can be found in the fstab article.

Mount Commands

The mount command on its own mounts FreeBSD formatted (or UFS or UFS2) file systems. In order to mount foreign (or non-native FreeBSD formatted) file systems each supported file system has its own mount command in the format of 'mount_filesystem'; as an example the supported 'MS-DOS' (or DR-DOS, FAT16 or FAT32) formatted file system has the command 'mount_msdosfs'.

The following file systems are supported by FreeBSD:

CD-ROM

The mount_cd9660 command mounts file systems formatted using ISO 9660. This is limited to optical media conforming to CD-ROM standards and can include writable CD-R and re-writable CD-RW medium.

Example:

# mount_cd9660 /dev/acd0 /cdrom
# ls /cdrom/
.cshrc          INSTALL.HTM     boot.catalog    media           sys
.profile        INSTALL.TXT     cdrom.inf       mnt             tmp
6.3-RELEASE     README.HTM      dev             packages        tools
COPYRIGHT       README.TXT      docbook.css     proc            usr
ERRATA.HTM      RELNOTES.HTM    etc             rescue          var
ERRATA.TXT      RELNOTES.TXT    floppies        root
HARDWARE.HTM    bin             lib             sbin
HARDWARE.TXT    boot            libexec         stand

devfs

mount_devfs

DVD

mount_udf

File Descriptor

mount_fdescfs

Linux ext2

mount_ext2fs

linux Process

mount_linprocfs

Linux System

mount_linsysfs

MFS

mount_mfs

Microsoft DOS (FAT16 or FAT32)

mount_msdosfs

Microsoft NT (NTFS)

mount_ntfs

Null

mount_nullfs

Process

mount_procfs

Reiser

mount_reiserfs

Standard

mount_std

UMAP

mount_umapfs

Union

mount_unionfs

Unix Network Share

mount_nfs

Unix Network Share (version 4)

mount_nfs4