Editing File system (section)

===Unix and Unix-like operating systems===
[[Unix-like]] operating systems create a virtual file system, which makes all the files on all the devices appear to exist in a single hierarchy. This means, in those systems, there is one [[root directory]], and every file existing on the system is located under it somewhere. Unix-like systems can use a [[RAM disk]] or network shared resource as its root directory.

Unix-like systems assign a device name to each device, but this is not how the files on that device are accessed. Instead, to gain access to files on another device, the operating system must first be informed where in the directory tree those files should appear. This process is called [[mount (computing)|mounting]] a file system. For example, to access the files on a [[CD-ROM]], one must tell the operating system "Take the file system from this CD-ROM and make it appear under such-and-such directory." The directory given to the operating system is called the ''[[mount point]]''&nbsp;– it might, for example, be {{mono|/media}}. The {{mono|/media}} directory exists on many Unix systems (as specified in the [[Filesystem Hierarchy Standard]]) and is intended specifically for use as a mount point for removable media such as CDs, DVDs, USB drives or floppy disks. It may be empty, or it may contain subdirectories for mounting individual devices. Generally, only the [[System administrator|administrator]] (i.e. [[root user]]) may authorize the mounting of file systems.

[[Unix-like]] operating systems often include software and tools that assist in the mounting process and provide it new functionality. Some of these strategies have been coined "auto-mounting" as a reflection of their purpose.
* In many situations, file systems other than the root need to be available as soon as the operating system has [[booting|booted]]. All Unix-like systems therefore provide a facility for mounting file systems at boot time. [[System administrator]]s define these file systems in the configuration file [[fstab]] (''vfstab'' in [[Solaris (operating system)|Solaris]]), which also indicates options and mount points.
* In some situations, there is no need to mount certain file systems at [[booting|boot time]], although their use may be desired thereafter. There are some utilities for Unix-like systems that allow the mounting of predefined file systems upon demand.
* Removable media allow programs and data to be transferred between machines without a physical connection. Common examples include [[USB flash drive]]s, [[CD-ROM]]s, and [[DVD]]s. Utilities have therefore been developed to detect the presence and availability of a medium and then mount that medium without any user intervention.
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* Progressive Unix-like systems have also introduced a concept called '''supermounting'''; see, for example, [http://sourceforge.net/projects/supermount-ng the Linux supermount-ng project]. For example, a floppy disk that has been supermounted can be physically removed from the system. Under normal circumstances, the disk should have been synchronized and then unmounted before its removal. Provided synchronization has occurred, a different disk can be inserted into the drive. The system automatically notices that the disk has changed and updates the mount point contents to reflect the new medium.
* An [[automounter]] will automatically mount a file system when a reference is made to the directory atop which it should be mounted. This is usually used for file systems on network servers, rather than relying on events such as the insertion of media, as would be appropriate for removable media.

===={{Anchor|LINUX}}Linux====
[[Linux]] supports numerous file systems, but common choices for the system disk on a block device include the ext* family ([[ext2]], [[ext3]] and [[ext4]]), [[XFS]], [[JFS (file system)|JFS]], and [[btrfs]]. For raw flash without a [[flash translation layer]] (FTL) or [[Memory Technology Device]] (MTD), there are [[UBIFS]], [[JFFS2]] and [[YAFFS]], among others. [[SquashFS]] is a common compressed read-only file system.

====Solaris====
[[Solaris (operating system)|Solaris]] in earlier releases defaulted to (non-journaled or non-logging) [[Unix File System|UFS]] for bootable and supplementary file systems. Solaris defaulted to, supported, and extended UFS.

Support for other file systems and significant enhancements were added over time, including [[Veritas Software]] Corp. (journaling) [[VxFS]], Sun Microsystems (clustering) [[QFS]], Sun Microsystems (journaling) UFS, and Sun Microsystems (open source, poolable, 128 bit compressible, and error-correcting) [[ZFS]].

Kernel extensions were added to Solaris to allow for bootable Veritas [[VxFS]] operation. Logging or [[Journaling file system|journaling]] was added to UFS in Sun's [[Solaris 7]]. Releases of [[Solaris 10]], Solaris Express, [[OpenSolaris]], and other open source variants of the Solaris operating system later supported bootable [[ZFS]].

[[Logical Volume Management]] allows for spanning a file system across multiple devices for the purpose of adding redundancy, capacity, and/or throughput. Legacy environments in Solaris may use [[Solaris Volume Manager]] (formerly known as [[Solstice DiskSuite]]). Multiple operating systems (including Solaris) may use [[Veritas Volume Manager]]. Modern Solaris based operating systems eclipse the need for volume management through leveraging virtual storage pools in [[ZFS]].

====macOS====
[[macOS|macOS (formerly Mac OS X)]] uses the [[Apple File System]] (APFS), which in 2017 replaced a file system inherited from [[classic Mac OS]] called [[HFS Plus]] (HFS+). Apple also uses the term "Mac OS Extended" for HFS+.<ref>{{cite web|title=Mac OS X: About file system journaling|url=http://support.apple.com/kb/ht2355|publisher=Apple|access-date=8 February 2014}}</ref> HFS Plus is a [[metadata (computing)|metadata]]-rich and [[case preservation|case-preserving]] but (usually) [[case sensitivity|case-insensitive]] file system. Due to the Unix roots of macOS, Unix permissions were added to HFS Plus. Later versions of HFS Plus added journaling to prevent corruption of the file system structure and introduced a number of optimizations to the allocation algorithms in an attempt to defragment files automatically without requiring an external defragmenter.

File names can be up to 255 characters. HFS Plus uses [[Unicode]] to store file names. On macOS, the [[file format|filetype]] can come from the [[type code]], stored in file's metadata, or the [[filename extension]].

HFS Plus has three kinds of links: Unix-style [[hard link]]s, Unix-style [[symbolic link]]s, and [[alias (Mac OS)|aliases]]. Aliases are designed to maintain a link to their original file even if they are moved or renamed; they are not interpreted by the file system itself, but by the File Manager code in [[userland (computing)|userland]].

macOS 10.13 High Sierra, which was announced on June 5, 2017, at Apple's WWDC event, uses the [[Apple File System]] on [[solid-state drive]]s.

macOS also supported the [[Unix File System|UFS]] file system, derived from the [[BSD]] Unix Fast File System via [[NeXTSTEP]]. However, as of [[Mac OS X Leopard]], macOS could no longer be installed on a UFS volume, nor can a pre-Leopard system installed on a UFS volume be upgraded to Leopard.<ref>{{cite web|url=http://docs.info.apple.com/article.html?artnum=306516|title=Mac OS X 10.5 Leopard: Installing on a UFS-formatted volume|work=apple.com|date=19 October 2007|access-date=29 April 2016|archive-url=https://web.archive.org/web/20080316033439/http://docs.info.apple.com/article.html?artnum=306516|archive-date=16 March 2008|url-status=dead}}</ref> As of [[Mac OS X Lion]] UFS support was completely dropped.

Newer versions of macOS are capable of reading and writing to the legacy [[File Allocation Table|FAT]] file systems (16 and 32) common on Windows. They are also capable of ''reading'' the newer [[NTFS]] file systems for Windows. In order to ''write'' to NTFS file systems on macOS versions prior to [[Mac OS X Snow Leopard]] third-party software is necessary. Mac OS X 10.6 (Snow Leopard) and later allow writing to NTFS file systems, but only after a non-trivial system setting change (third-party software exists that automates this).<ref>{{cite web|last=OSXDaily|title=How to Enable NTFS Write Support in Mac OS X|url=http://osxdaily.com/2013/10/02/enable-ntfs-write-support-mac-os-x/|access-date=6 February 2014|date=2013-10-02}}</ref>

Finally, macOS supports reading and writing of the [[exFAT]] file system since Mac OS X Snow Leopard, starting from version 10.6.5.<ref name="encase-book">{{cite book|url=https://books.google.com/books?id=c1mezk6uHfIC&q=os+x+exfat+10.6.5&pg=PA79 |title=EnCase Computer Forensics - The Official EnCE: EnCase Certified Examiner |author=Steve Bunting |date=2012-08-14 |publisher=Wiley |access-date=2014-02-07|isbn=9781118219409 }}</ref>