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Mount

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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.

Contents

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 exists on its own a command to mount FreeBSD formatted file systems. In order to permit the mounting of 'foreign' (or non-native FreeBSD formatted) file systems each supported file system has its own mount command using the common naming scheme of 'mount_filesystem'. The command to mount an 'MS-DOS' (or DR-DOS, FAT16 or FAT32) formatted file system the command is 'mount_msdosfs'. The file systems available to FreeBSD and the associated mount commands are as follows:

mount_cd9660

mount_devfs

mount_ext2fs

mount_fdescfs

mount_linprocfs

mount_linsysfs

mount_mfs

mount_msdosfs

mount_nfs

mount_nfs4

mount_ntfs

mount_nullfs

mount_procfs

mount_reiserfs

mount_std

mount_udf

mount_umapfs

mount_unionfs

See Also

See also related articles: umount and etc/fstab

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