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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.
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.
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:
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 - though this is limited to read-only. Applications within the ports system are available to create (or write) to CD-R and CD-RW media.
# 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
The mount_udf command mounts file systems formatted using Universal Disk Format. This is limited to optical media conforming to DVD-ROM standards and can include writable DVD-R, DVD+R and re-writable DVD-RW, DVD+RW and DVD-RAM medium - though this is limited to read-only and to data DVDs. Applications within the ports system are available to create (or write) to the various DVD media. Video DVDs are typically encrypted to stop piracy and as such may not mount successfully.
The mount_ext2fs command mounts file systems formatted using Second Extended ext2 (but not the newer ext3 or ext4). This is typically the format used in the GNU/Linux kernel (sometimes referred to as an operating system). FreeBSD supports reading from this file system.
The mount_linprocfs command forms part of the Linux binary emulation layer available in FreeBSD.
The mount_linsysfs command forms part of the Linux binary emulation layer available in FreeBSD.
Microsoft DOS (FAT16 or FAT32)
The mount_msdosfs command mounts file systems formatted using File Allocation Table. This is typically the format used in older versions of Microsoft Windows as well as common memory cards and USB memory keys. FreeBSD supports reading and writing to this file system.
Example (using a USB memory key):
# mkdir /mnt/usb # mount_msdosfs /dev/da0s1 /mnt/usb # ls /mnt/usb/ BackupA1 Drivers BackupA2 Listing BackupA3 Support #
The above example creates the initial mount-point for the USB memory key using the mkdir command. This needs to be done only once.
The mount_smbfs command mounts file file systems located on network shares using the Samba protocol. This protocol is available with Microsoft Windows Server operating systems (where it is referred to by CIFS, the Common Internet File System) as well as other servers capable of hosting the CIFS protocol. The mount_samba command is used on one system to access the file system of another hosting the CIFS share.
Note: The mount_smbfs command is not available as part of the default FreeBSD installation. It is available from the ports system.
Microsoft NT (NTFS)
The mount_ntfs command mounts file systems formatted using Microsoft's proprietary New Technology File System. This is typically the format used in newer versions of Microsoft Windows. FreeBSD supports reading from this file system. There are projects actively working towards supporting the writing to this file system in various stages of progress however it is strongly recommended that read-only access to NTFS file systems is used on essential data drives.
The mount_reiserfs command mounts file systems formatted using Reiser (but not the newer Resier version 4). This is privately developed file system created by Hans Reiser through his Namesys company though the file system is available for free on open source operating systems. FreeBSD supports reading from this file system.
The mount_nfs command mounts file systems located on network shares using the NFS protocol. This protocol is available with the default FreeBSD installation as well as almost all known UNIX and Unix-line operating systems. The mount_nfs command is used on one system to access the file system of another hosting the NFS share.
The mount_nfs4 command mounts file systems located on network shares using the NFS protocol, specifically version 4. This command is used to connect to newer versions NFS shares, which offer improved functionality, but otherwise maintains similarly to the previous NFS versions.
Unless otherwise stated above (such as the read-only aspect of certain listed file systems) the limitations of the file system implementation on FreeBSD is typically based on the design of a given file system. For example the MS-DOS file system variation called FAT16 has a physical partition (or slice in FreeBSD terminology) size limitation of 2GB. Another example could be network based shares using NFS or CIFS where the server hosting the share could place specific read/write attributes and thereby control the access available to the client system mounting that share.