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.
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:
