Editing Ext2 (section)

{{For|the gene|EXT2 (gene)}}
{{short description|File system for the Linux kernel}}
{{lowercase}}
{{Infobox file system
| name = ext2
| full_name = Second extended file system
| developer = [[Rémy Card]]
| introduction_os = [[Linux]]
| introduction_date = January 1993
| preceded_by       = [[extended file system]]
| succeeded_by      = [[ext3]]
| partition_id = <code>[[Basic Data Partition|EBD0A0A2-B9E5-4433-87C0-68B6B72699C7]]</code> ([[GUID Partition Table|GPT]])<br /><code>0x83</code> ([[Master Boot Record]])<br /><code>Apple_UNIX_SVR2</code> ([[Apple Partition Map]])
| directory_struct = Table
| file_struct = bitmap (free space), table (metadata)
| bad_blocks_struct = Table
| max_filename_size = 255 bytes
| max_files_no = 10<sup>18</sup>
| max_volume_size = 2–32 [[tebibyte|TiB]]
| max_file_size = 16 [[gibibyte|GiB]] – 2 [[tebibyte|TiB]]
| filename_character_set = All bytes except [[Null character|NUL]] ('\0') and '/'
| dates_recorded = modification (mtime), attribute modification (ctime), access (atime)
| date_range = December 14, 1901 - [[Year 2038 problem|January 18, 2038]]
| date_resolution = 1&nbsp;s
| forks_streams =
| attributes = 
| file_system_permissions = Unix permissions, [[Access-control_list#POSIX_ACL|POSIX Access Control Lists]] (ACL)
| compression = No (Available through patches)
| encryption = No
| OS = [[Linux]], [[BSD]],<ref>{{Cite web |title=Chapter 8. Disks, File Systems, and Boot Loaders |url=https://www.freebsd.org/doc/en_US.ISO8859-1/books/faq/disks.html#idp59236072 |access-date=11 April 2018 |website=www.freebsd.org}}</ref><ref>{{Cite web |title=ext2fs(5) |url=https://www.freebsd.org/cgi/man.cgi?query=ext2fs&sektion=5&manpath=freebsd-release-ports |access-date=11 April 2018 |website=www.freebsd.org}}</ref> [[ReactOS]],<ref>{{Cite web |title=ReactOS 0.4.2 Released |url=https://reactos.org/project-news/reactos-042-released |access-date=17 August 2016 |website=reactos.org}}</ref> Windows (through an [[Installable File System|IFS]]), [[macOS]] (through [[Filesystem_in_Userspace|FUSE]]), [[HelenOS]],<ref>{{Cite web |title=HelenOS Wiki: Ext4fs |url=https://www.helenos.org/wiki/Fs/Ext4fs |access-date=6 November 2023 |website=www.helenos.com}}</ref> [[RIOT (operating system)|RIOT]],<ref>{{Cite web |title=pkg/lwext4: add lightweight implementation of the ext2/3/4 filesystem |url=https://github.com/RIOT-OS/RIOT/pull/18682 |access-date=6 November 2023 |website=www.github.com}}</ref> [[Zephyr (operating system)|Zephyr]]<ref>{{Cite web |title=subsys: fs: Implementation of ext2 file system |url=https://github.com/zephyrproject-rtos/zephyr/pull/55152 |access-date=6 November 2023 |website=www.github.com}}</ref>

}}

'''ext2''', or '''second extended file system''', is a [[file system]] for the [[Linux]] [[kernel (operating system)|kernel]].  It was initially designed by French software developer [[Rémy Card]] as a replacement for the [[extended file system]] (ext). Having been designed according to the same principles as the [[Berkeley Fast File System]] from [[Berkeley Software Distribution|BSD]], it was the first commercial-grade filesystem for Linux.<ref>{{Cite book |last=Mauerer |first=Wolfgang |url=https://books.google.com/books?id=-6zvRFEfQ24C&pg=PT490 |title=Professional Linux Kernel Architecture |publisher=John Wiley & Sons |year=2010 |isbn=9781118079911}}</ref>

The canonical implementation of ext2 is the "ext2fs" filesystem driver in the Linux kernel. Other implementations (of varying quality and completeness) exist in [[GNU Hurd]],<ref>{{Cite web |title=GNU Hurd/ hurd/ translator/ ext2fs |url=https://www.gnu.org/software/hurd/hurd/translator/ext2fs.html |access-date=2024-02-10 |website=GNU Hurd}}</ref> [[MINIX 3]],<ref>{{Cite web |title=MINIX Release 3.2.0 |url=https://wiki.minix3.org/doku.php?id=releases:3.2.0:start |access-date=2024-02-10 |website=MINIX 3}}</ref><ref>{{Cite web |title=git.minix3.org Git - minix.git/tree - minix/fs/ext2/ |url=https://git.minix3.org/index.cgi?p=minix.git;a=tree;f=minix/fs/ext2 |access-date=2024-02-10 |website=MINIX 3 Source Code}}</ref> some [[BSD]] kernels,<ref>{{Cite web |title=NetBSD src/sys/ufs/ext2fs/ |url=http://cvsweb.netbsd.org/bsdweb.cgi/src/sys/ufs/ext2fs/ |access-date=2024-02-10 |website=NetBSD Source Code}}</ref><ref>{{Cite web |title=OpenBSD src/sys/ufs/ext2fs/ |url=https://cvsweb.openbsd.org/cgi-bin/cvsweb/src/sys/ufs/ext2fs/ |access-date=2024-02-10 |website=OpenBSD Source Code}}</ref><ref>{{Cite web |title=ext2fs « fs « sys - src - FreeBSD source tree |url=https://cgit.freebsd.org/src/tree/sys/fs/ext2fs |access-date=2024-02-10 |website=FreeBSD Source Code}}</ref> in [[MiNT]],<ref>{{Cite web |title=freemint/sys/xfs/ext2fs at master · freemint/freemint |url=https://github.com/freemint/freemint/tree/master/sys/xfs/ext2fs |access-date=2024-02-10 |website=FreeMiNT Source Code}}</ref> [[Haiku (operating system)|Haiku]]<ref>{{Cite web |title=ext2 « file_systems « kernel « add-ons « src - haiku - Haiku's main repository |url=https://git.haiku-os.org/haiku/tree/src/add-ons/kernel/file_systems/ext2 |access-date=2024-02-10 |website=Haiku Source Code}}</ref> and as third-party [[Microsoft Windows]]<ref>{{Cite web |title=matt-wu/Ext3Fsd: Ext2/3/4 file system driver for Windows |url=https://github.com/matt-wu/Ext3Fsd |access-date=2024-02-10 |website=matt-wu/Ext3Fsd}}</ref> and [[macOS]] (via [[Filesystem_in_Userspace|FUSE]]) drivers. This driver was deprecated in Linux version 6.9 in favor of the ext4 driver, as the ext4 driver works with ext2 filesystems.<ref name="phoronix-deprecated" />

ext2 was the default filesystem in several [[Linux distribution]]s, including [[Debian]] and [[Red Hat Linux]], until supplanted by [[ext3]], which is almost completely compatible with ext2 and is a [[journaling file system]]. ext2 is still the filesystem of choice for [[Flash memory|flash]]-based storage media (such as [[SD card]]s and [[USB flash drive]]s){{citation needed|date=February 2024}} because its lack of a journal increases performance and minimizes the number of writes, and flash devices can endure a limited number of write cycles.{{dubious|date=February 2025|reason=The minor benefit here is far offset by the risk of file system corruption. Plus ext4 allows you to reduce or turn off journaling so you'd use that instead. I'll wait a bit but this should probably be quickly removed unless compelling sources are given.}} Since 2009,<ref>{{Cite web |title=ext4: Allow ext4 to run without a journal |url=https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=0390131ba84fd3f726f9e24fc4553828125700bb |access-date=12 January 2021 |website=Linux kernel source tree}}</ref> the [[Linux kernel]] supports a journal-less mode of [[ext4]] which provides benefits not found with ext2, such as larger file and volume sizes.<ref>{{Cite web |title=Linux File Systems: Ext2 vs Ext3 vs Ext4 |url=https://www.thegeekstuff.com/2011/05/ext2-ext3-ext4/ |access-date=2020-07-13 |website=www.thegeekstuff.com}}</ref>