Mount point

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As mount ( English mount point ) is under UNIX-like operating systems , the place in the directory structure referred to which a resource mounted, English mounted or Neudeutsch mounted , is. Depending on the operating system , a mountable data storage device or file system , for example in a drive or on a partition , is also referred to as a drive letter or volume .

Unix

Under Unix and on Unix -like systems , for example Linux or macOS , data storage media - "drives" - are mapped as block-oriented device files . The name of these device files differs depending on the operating system and can also differ on the same operating system, e.g. B. differentiate according to the type of connection ( SCSI , ATA ...). In addition to hierarchically oriented naming schemes, such as how the devices are connected, there are also logical ones that only reflect the type of device connected. In Linux, for example, the first two characters usually stand for the type of drive, the third for the number; this is /dev/hdathe name of the first ATA hard disk, /dev/sdbthe second SCSI hard disk or /dev/fd2the third floppy disk drive . On the other hand, the connection used on the system makes no difference under macOS, the first hard drive is always called /dev/disk0. MacOS does not support internal floppy drives at all, however external USB floppy drives can be used. Common to all Unix-type operating systems are the logical device names that correspond to the partitions found on the data storage device, e.g. /dev/sda1for the first partition on the first ATA device under Linux, which corresponds /dev/disk0s0to macOS.

The block-oriented raw data of the underlying logical data memory is accessed via the device name. It is u. a. the formatting is carried out and a file system is created. The file system must be supported by the operating system, then its content finally appears at the specified location in the system-wide directory structure through the integration  - it is mounted there in a directory that must already exist. Within the directory structure, which in its entirety is also referred to as the Unix file system , normal access does not subsequently take place via device names, but via the directory used when mounting, i.e. via the location within the directory structure used for mounting.

The command with which a volume can be mounted is called mount; the process is as suspending, integration or mounting ( English to mount hereinafter). The command to unmount a disk is called umount. Mounted data carriers must be removed from the directory structure again ( English unmount ) before they can be removed from the drive again. This is important because otherwise data could be lost, as data from the cache will be written back to the data carrier when unmounted. In many cases, methods are used that automatically integrate a data carrier after it has been connected or inserted ( automounter ).

By mounting the directory structure on the mount point below the root directory ( English root directory represented by the /) around those structures extended that contains the file system of the hinged disc. For applications it does not matter which data carrier a file is on, since the operating system takes over the management and you only have to know the relevant path through the directory structure.

The logical data stores that are important for a system, e.g. B. partitions are automatically mounted at system start and unmounted again at shutdown. The mount points used for this are specified in the file (for filesystem table ), in which properties and mount options can also be predefined. This includes user rights, write rights, read rights as well as options specific to the respective file system. /etc/fstab

The for the dynamic integration of z. B. Subdirectories intended for removable media depend on the configuration. According to the file system hierarchy standard , the mount point is /mediaprovided for this, whereby the name for the subdirectory is e.g. B. the name or the serial number of the integrated file system ( volume label or volume serial number ) is used. This is the normal case with Linux, but in earlier versions there were also places in the directory tree (without file system designation) , for example /cdromor /mnt/cdromfor CD-ROMs . With macOS, /Volumesthe standard directory is in which the file systems are integrated with their names. For example, if a volume is called “data”, this file system can be found in /Volumes/Daten. This corresponds to under Linux /media/Daten.

The Apple operating system macOS, formerly Mac OS X and OS X, knows not only the Unix-typical commands mountand unmountalso the utility programs diskutil(from Mac OS X 10.2 "Jaguar"), with old versions of Mac OS X also disktoolfor data storage and their Manage file systems. The commands can be B. can be used on the terminal or in single-user mode .

DOS and Windows

On Microsoft operating systems, MS-DOS , compatible to DOS and Windows mount points are used as drive letters referred. Historically, these come from the MS-DOS forerunner CP / M and designate mountable file systems or volumes with a letter from A – Z , followed by a colon , i.e. A:to Z:. This convention was also continued under Windows 9x and Windows NT , but this also limits the number of mountable file systems to 26. As of Windows NT 4.0 , file systems can also be mounted as subdirectories .

Traditionally, A:and denote B:the two possible floppy disk drives of the IBM PC and compatible computer , and C:the boot partition of the hard disk and, if no other hard disks (partitions) are available, D:the computer's CD / DVD drive.

The order in which drive letters are assigned depends on MS-DOS-based systems and, to a certain extent, also on NT-based systems (boot drive), on the way these drives are connected (e.g. IDE channel and jumpers), on the order in which the other drivers and, if necessary, from the manual drive letter assignment in the control panel .

CD and DVD drives as well as memory card readers have their own drive letters (for readers with multiple slots, each slot has its own drive letter, as each slot is viewed as a separate drive). USB memory sticks are automatically assigned their own letters when they are inserted - during operation. This is the case from Windows 2000 , with drivers from other providers already from Windows 98 . Drive letters can also be assigned for network access on another computer ( network drive ). With the command line command subst , directories can be assigned their own drive letter.

Due to the market dominance of Windows, drive letters have also been adopted on other systems, for example on the PlayStation from Sony .

Individual evidence

  1. ^ Daniel Knight: Floppy Disk Compatibility and Incompatibility in the Mac World. In: Low End Mac Tech Journal. August 16, 2016, accessed on March 23, 2020 : “When Apple introduced Mac OS X, one thing it didn't do is provide drivers for the Mac's internal floppy drives. It does support USB floppy drives ... "
  2. ↑ Aeleen fresh: Unix system administration . O'Reilly Germany, 2003, 2: The Unix Philosophy, p. 66, footnote 13 ( full text in Google Book Search): “The term file system thus refers on the one hand to the higher-level directory tree of the system, which includes all hard drive partitions of the system that the user can access (as in» the Unix file system «), On the other hand to the files and directories on the individual hard disk partitions (as in“ Setting up a file system on a hard disk partition ”or“ Mounting the user file system ”). Only from the context does it become clear which of the two meanings of the term is meant. "
  3. ↑ Disk arbitration. (No longer available online.) In: Technical Note TN2053. Apple, September 4, 2002, archived from the original ; accessed on March 22, 2020 (English).
  4. ↑ How to start up your Mac in single user mode or verbose log mode. Apple, February 29, 2020, accessed March 22, 2020 .
  5. ^ Thomas Armbrüster: Single-user mode. Macwelt, January 6, 2011, accessed March 22, 2020 .