imported>Nathan Hadley (Pigeon): Corrected grammar.

2024-09-13T12:48:37Z

Corrected grammar.

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{{Short description|Metadata associated with computer file that define file system behavior}}
'''File attributes''' are a type of [[metadata]] that describe and may modify how [[Computer file|files]] and/or [[Directory (file systems)|directories]] in a [[filesystem]] behave. Typical file attributes may, for example, indicate or specify whether a file is visible, modifiable, compressed, or encrypted. The availability of most file attributes depends on support by the underlying filesystem (such as [[File Allocation Table|FAT]], [[NTFS]], [[ext4]])
where attribute data must be stored along with other control structures. Each attribute can have one of two states: set and cleared. Attributes are considered distinct from other metadata, such as dates and times, [[filename extension]]s or [[file system permissions]]. In addition to files, [[folder (computing)|folder]]s, [[volume (computing)|volume]]s and other file system objects may have attributes.

==DOS and Windows==
Traditionally, in [[DOS]] and [[Microsoft Windows]], [[computer file|file]]s and [[folder (computing)|folder]]s accepted four attributes:<ref name=pcmag-t /><ref name=computerhope-t /><ref name=IndianaUni-t />
* '''[[Archive bit|Archive]]''' (A): When set, it indicates that the hosting file has changed since the last [[backup]] operation. Windows' file system sets this attribute on any file that has changed. Backup software then has the duty of clearing it upon a successful full or incremental backup (not a differential one).
* '''Hidden''' (H): When set, indicates that the hosting file is hidden. MS-DOS commands like <code>[[dir (command)|dir]]</code> and Windows apps like [[File Explorer]] do not show hidden files by default, unless asked to do so.<ref>{{cite web|title=What is a hidden file?|url=http://windows.microsoft.com/en-US/windows7/What-is-a-hidden-file|work=Windows 7 Help|publisher=Microsoft|access-date=2 December 2012}}</ref>
* '''System''' (S): When set, indicates that the hosting file is a critical system file that is necessary for the computer to operate properly. MS-DOS and Microsoft Windows use it to mark important system files. MS-DOS commands like <code>dir</code> and Windows apps like File Explorer do not show system files by default even when hidden files are shown, unless asked to do so.
* '''Read-only''' (R): When set, indicates that a file should not be altered. Upon opening the file, file system [[API]] usually does not grant write permission to the requesting application, unless the application explicitly requests it. Read-only attributes on folders are usually ignored, being used for another purpose.<ref name="hidden and readonly"/><ref>{{cite web|title=Why is the readonly property on folders so strange?|url=https://devblogs.microsoft.com/oldnewthing/20030930-00/?p=42353}}</ref>

As new versions of Windows came out, Microsoft has added to the inventory of available attributes on the [[NTFS]] file system,<ref name="microsoft-full" /> including but not limited to:<ref>{{cite web|title=HOW TO: Use the File Attribute Management Script (Fileattributes.pl) in Windows 2000|url=http://support.microsoft.com/kb/320050|work=Microsoft support|publisher=Microsoft|access-date=2 December 2012}}</ref>
* '''Compressed''' (C): When set, Windows [[data compression|compresses]] the hosting file upon storage. For more information, see {{section link|NTFS|File compression}}.
* '''Encrypted''' (E): When set, Windows [[filesystem-level encryption|encrypts]] the hosting file upon storage to prevent unauthorized access. For more information, see {{section link|NTFS|Encryption}}.
* '''Not Content-Indexed''' (I): When set, [[Indexing Service]] or [[Windows Search]] do not include the hosting file in their indexing operation.

Other attributes that are displayed in the "Attributes" column of Windows Explorer<ref name="microsoft-full"/> include:
* '''Directory''' (D): The entry is a [[Directory (computing)|subdirectory]], containing file and directory entries of its own.
* '''Reparse Point''' (L): The file or directory has an associated re-parse point, or is a [[symbolic link]].
* '''Offline''' (O): The file data is physically moved to offline storage (Remote Storage).
* '''Sparse''' (P): The file is a [[sparse file]], i.e., its contents are partially empty and non-contiguous.
* '''Temporary''' (T): The file is used for temporary storage.

In DOS, [[OS/2]] and Windows, the <code>[[attrib]]</code> command in [[cmd.exe]] and [[command.com]] can be used to change and display the four traditional file attributes.<ref name=IndianaUni-t /><ref name=pcmag-attrib.exe /> File Explorer in Windows can show the seven mentioned attributes but cannot set or clear the System attribute.<ref name="hidden and readonly" /> [[Windows PowerShell]], which has become a component of [[Windows 7]] and later, features two commands that can read and write attributes: <code>Get-ItemProperty</code> and <code>Set-ItemProperty</code>.<ref>{{cite web|title=Use a PowerShell Cmdlet to Work with File Attributes|url=http://blogs.technet.com/b/heyscriptingguy/archive/2011/01/26/use-a-powershell-cmdlet-to-work-with-file-attributes.aspx|work=Hey, Scripting Guy! Blog|publisher=Microsoft|access-date=3 December 2012|date=26 January 2011}}</ref> To change an attribute on a file on [[Windows NT]], the user must have appropriate [[file system permissions]] known as ''Write Attributes'' and ''Write Extended Attributes''.<ref>{{cite web|title=How to set, view, change, or remove special permissions for files and folders in Windows XP|url=http://support.microsoft.com/kb/308419|work=Microsoft Support|publisher=Microsoft|access-date=2 December 2012|date=7 May 2007}}</ref>

==Unix and POSIX==
In [[Unix]] and Unix-like systems, including [[POSIX]]-conforming systems, each file has a 'mode' containing 9 bit flags controlling read, write and execute permission for each of the file's owner, group and all other users (see [[File-system permissions#Traditional Unix permissions|File-system permissions §Traditional Unix permissions]] for more details) plus the [[setuid|''setuid'' and ''setgid'']] bit flags and a [[sticky bit|'sticky' bit flag]].
The mode also specifies the [[Unix file types|file type]] (regular file, directory, or some other special kind).

===4.4BSD and derivatives===
In [[4.4BSD]] and [[4.4BSD-Lite]], files and directories (folders) accepted four attributes that could be set by the owner of the file or the [[superuser]] (the "User" attributes) and two attributes that could only be set by the superuser (the "System" attributes):<ref>{{man|2|chflags|4.4BSD-Lite2}}</ref>
* '''(User) No-dump''': When set, it indicates that the file or directory should not be saved during a [[backup]] operation.
* '''(User and System) Immutable''': When set, indicates that the file or directory should not be altered. Attempts to open the file for writing, create a file within the directory, remove a file from the directory, rename a file within the directory, rename the file or directory, or remove the file or directory will fail with a permissions error.
* '''(User and System) Append-only''': When set, indicates that the file should only be appended to.
* '''(User) Opaque''': When set on a directory, indicates that the directory is opaque when viewed through a [[Union mount|union stack]].

[[FreeBSD]] added some additional attributes,<ref name="freebsd-flags">{{man|2|chflags|FreeBSD}}</ref> also supported by [[DragonFly BSD]]:<ref name="dragonflybsd-flags">{{man|2|chflags|DragonFly BSD}}</ref>
* '''(User and System) No-unlink''': When set, indicates that the file or directory should not be renamed or removed. Attempts to rename or remove the file or directory will fail with a permissions error.

FreeBSD also supports:<ref name="freebsd-flags"/>
* '''(System) No-archive''': When set, indicates that the file or directory should not be archived.
* '''(System) Snapshot''': When set, indicates that the file or directory is a snapshot file. This attribute is maintained by the system, and cannot be set, even by the super-user.

whereas DragonFly BSD supports:<ref name="dragonflybsd-flags"/>
* '''(User and System) No-history''': When set, indicates that history should not be retained for the file or directory.
* '''(User) Swapcache''': When set, indicates that clean filesystem data for the file, or for the directory and everything underneath the directory, should be cached in swap space on a [[solid-state drive]].
* '''(System) Swapcache''': When set, indicates that clean filesystem data for the file, or for the directory and everything underneath the directory, should ''not'' be cached in swap space on a solid-state drive.
* '''(System) Archived''': When set, indicates that the file or directory may be archived.

[[NetBSD]] added another attribute,<ref>{{man|2|chflags|NetBSD}}</ref> also supported by [[OpenBSD]]:<ref>{{man|2|chflags|OpenBSD}}</ref>
* '''(System) Archived''': When set, indicates that the file or directory is archived.

[[macOS]] added three attributes:
* '''(User) Hidden''': When set, indicates that the file or directory should not, by default, be displayed in the GUI; [[ls]] will display it, however.<ref>{{man|2|chflags|Darwin}}</ref>
* '''(System) Restricted''': When set, indicates that the file or directory will be protected by [[System Integrity Protection]]
* '''(User and System) Compressed''': Read-only attribute for files compressed using [[HFS_Plus|HFS+]] Compression

In these systems, the <code>[[chflags]]</code> and <code>[[ls]]</code> commands can be used to change and display file attributes. To change a "user" attribute on a file in 4.4BSD-derived operating systems, the user must be the owner of the file or the superuser; to change a "system" attribute, the user must be the superuser.

===Linux===
The [[Linux]] operating system can support a [[Chattr#Attributes|wide range of file attributes]] that can be listed by the <code>lsattr</code> command and modified, where possible, by the <code>[[chattr]]</code> command.
Programs can examine and alter attributes using [[ioctl]] operations.<ref>{{man|2|ioctl_iflags|Linux}}</ref>

Many Linux file systems support only a limited set of attributes, and none of them support every attribute that <code>chattr</code> can change. File systems that support at least some attributes include [[ext4]], [[XFS]] and [[btrfs]].

{| class="wikitable sortable" style="margin-left:auto; margin-right:auto"
|+ Common file attributes supported by many common Linux file systems
|-

!Attribute
!{{mono|lsattr}} flag
!{{mono|chattr}} option
!Semantics and rationale
|-

!No <code>atime</code> updates
|style="text-align:center" |<code>A</code>
|<code>+A,-A</code>
|[[stat (Unix)|{{mono|atime}} record]] is not modified when file is read/accessed.
|-

!Append-only
|style="text-align:center" |<code>a</code>
|<code>+a,-a</code>
|
Writing to file only allowed in append mode.
|-

!Immutable
|style="text-align:center" |<code>i</code>
|<code>+i,-i</code>
|
Prevents any change to file's contents or metadata: file/directory cannot be written to, deleted, renamed, or hard-linked.
|-

!No dump
|style="text-align:center" |<code>d</code>
|<code>+d,-d</code>
|File is skipped by the [[dump (Unix)|{{mono|dump}} program]]
|-

!Secure deletion
|style="text-align:center" |<code>s</code>
|<code>+s,-s</code>
|Requests that, when deleted, all file data blocks are [[Data remanence#Overwriting|filled with zeroes]].
|-

!Synchronous updates
|style="text-align:center" |<code>S</code>
|<code>+S,-S</code>
|Changes are written synchronously to the underlying filesystem storage medium; equivalent to 'sync' mount option for affected files.
|-

|}

===OpenSolaris and derivatives===
Support for "system attributes" (in which the operating system defines the meaning, unlike general [[extended file attributes]]) was added to OpenSolaris in 2007 in support of the CIFS server.<ref>{{cite web |last1=Shellenbaum |first1=Mark |title=Extensible Attribute Interfaces [PSARC/2007/315] |url=https://illumos.org/opensolaris/ARChive/PSARC/2007/315/spec.final.txt |website=OpenSolaris ARC Material Archive |publisher=illumos.org |access-date=10 March 2023}}</ref> It has been carried forward from there into both the [[Oracle Solaris]] 11 releases and the open source [[illumos]] project.

In this implementation, a [https://docs.oracle.com/cd/E88353_01/html/E37853/sysattr-7.html wide range of attributes] can be set via the <code>[[chmod]]</code> command<ref>{{cite web |title=chmod(1) |url=https://docs.oracle.com/cd/E88353_01/html/E37839/chmod-1.html |website=Oracle Solaris 11.4 Reference Library: man pages section 1: User Commands |publisher=Oracle |access-date=10 March 2023}}</ref><ref>{{cite web |title=chmod(1) |url=https://illumos.org/man/1/chmod |website=illumos man pages |publisher=illumos.org |access-date=10 March 2023}}</ref> and listed by the <code>[[ls]]</code> command.<ref>{{cite web |title=ls(1) |url=https://docs.oracle.com/cd/E88353_01/html/E37839/ls-1.html |website=Oracle Solaris 11.4 Reference Library: man pages section 1: User Commands |publisher=Oracle |access-date=10 March 2023}}</ref><ref>{{cite web |title=ls(1) |url=https://illumos.org/man/1/ls |website=illumos man pages |publisher=illumos.org |access-date=10 March 2023}}</ref>
Programs can examine and alter attributes using the <code>getattrat</code> and <code>setattrat</code> functions.<ref>{{cite web |title=getattrat(3c)/setattrat(3c) |url=https://docs.oracle.com/cd/E88353_01/html/E37843/getattrat-3c.html |website=Oracle Solaris 11.4 Reference Library: man pages section 3: Basic Library Functions |publisher=Oracle |access-date=10 March 2023}}</ref><ref>{{cite web |title=getattrat(3c)/setattrat(3c) |url=https://illumos.org/man/3C/getattrat |website=illumos man pages |publisher=illumos.org |access-date=10 March 2023}}</ref>

Currently the [[ZFS]] file system supports all defined attributes, and starting in Oracle Solaris 11.2, the [[tmpfs]] file system supports a subset of attributes.<ref>{{cite web |title=sysattr(7) |url=https://docs.oracle.com/cd/E88353_01/html/E37853/sysattr-7.html |website=Oracle Solaris 11.4 Reference Library: man pages section 7 |publisher=Oracle |access-date=10 March 2023}}</ref>

{| class="wikitable sortable" style="margin-left:auto; margin-right:auto"
|+ Common file attributes supported by Oracle Solaris and illumos systems
|-

!Attribute
!Compact flag for {{mono|ls}} & {{mono|chmod}}
!Semantics and rationale
|-

!<code>appendonly</code>
|style="text-align:center" |<code>a</code>
|
Writing to file only allowed in append mode.
|-

!<code>immutable</code>
|style="text-align:center" |<code>i</code>
|
Prevents any change to file's contents or metadata (except access time): file/directory cannot be written to, deleted, or renamed.
|-

!<code>nodump</code>
|style="text-align:center" |<code>d</code>
|File should be skipped by backup programs
|-

!<code>nounlink</code>
|style="text-align:center" |<code>u</code>
|Prevents removing the file, but allows other changes.
|-

|}

==See also==
* [[Extended file attributes]]
* [[Hidden file and hidden directory]]
* [[Volume label]]

==References==
{{Reflist|refs=

<ref name="pcmag-t">{{cite web|title=Definition of: file attribute|url=https://www.pcmag.com/encyclopedia/term/file-attribute|work=[[PC Magazine]]|publisher=[[Ziff Davis]]|access-date=14 October 2020}}</ref>

<ref name="computerhope-t">{{cite web|title=File attributes|url=http://www.computerhope.com/jargon/f/fileattr.htm|work=Computer Hope|access-date=2 December 2012}}</ref>

<ref name="IndianaUni-t">{{cite web|title=In Windows, what are file attributes, and how can I change them?|work=Knowledge Base|publisher=[[Indiana University]]|access-date=2 December 2012|date=11 October 2011 |url=https://kb.iu.edu/d/aift}}</ref>

<ref name="microsoft-full">{{cite web |title=File Attribute Constants |url=https://docs.microsoft.com/en-us/windows/desktop/fileio/file-attribute-constants |work=[[MSDN]] |publisher=[[Microsoft]] |access-date=17 July 2018}}</ref>

<ref name=pcmag-attrib.exe>{{cite web|title=Definition of: DOS Attrib|url=https://www.pcmag.com/encyclopedia_term/0%2C2542%2Ct%3DDOS+Attrib%26i%3D41730%2C00.asp|work=[[PC Magazine]]|publisher=[[Ziff Davis]]|access-date=2 December 2012|archive-date=2 March 2012|archive-url=https://web.archive.org/web/20120302041859/http://www.pcmag.com/encyclopedia_term/0%2C2542%2Ct%3DDOS+Attrib%26i%3D41730%2C00.asp|url-status=dead}}</ref>

<ref name="hidden and readonly">{{cite web|title=You cannot view or change the Read-only or the System attributes of folders in Windows Server 2003, in Windows XP, in Windows Vista or in Windows 7|url=http://support.microsoft.com/kb/326549|work=Microsoft Support|publisher=Microsoft|access-date=2 December 2012|date=31 May 2012}}</ref>

}}
{{reflist|group=note}}

==External links==
* [https://www.pcmag.com/encyclopedia_term/0,2542,t=DOS+Attrib&i=41730,00.asp Definition of: DOS Attrib] {{Webarchive|url=https://web.archive.org/web/20120302041859/http://www.pcmag.com/encyclopedia_term/0%2C2542%2Ct%3DDOS+Attrib%26i%3D41730%2C00.asp |date=2012-03-02 }} on [[PC Magazine]]
* {{webarchive |url=https://web.archive.org/web/20071017224738/http://bellevuelinux.org/hidden_file.html |date=October 17, 2007 |title=Hidden files in Unix-like operating systems }}
* [https://learn.microsoft.com/en-us/cpp/c-runtime-library/file-attribute-constants File attribute constants], in [[C (programming language)|C]](-[[Runtime library|runtime-library]]), by Microsoft Learn, 10/26/2022
* [https://learn.microsoft.com/en-us/windows/win32/fileio/file-attribute-constants File Attribute Constants], in ([[Win32]]-)[[C++]], by Microsoft Learn, 06/09/2023

{{Computer files}}
{{File systems}}

{{DEFAULTSORT:File attribute}}
[[Category:Computer file systems]]

File attribute - Revision history

imported>Nathan Hadley (Pigeon): Corrected grammar.