Ext4

ext4 (fourth extended filesystem) is a journaling file system for Linux, developed as the successor to ext3.

ext4

Developer(s)	Mingming Cao, Andreas Dilger, Alex Zhuravlev (Tomas), Dave Kleikamp, Theodore Ts'o, Eric Sandeen, Sam Naghshineh, others
Full name	Fourth extended file system
Introduced	10 October 2006 with Linux 2.6.19
Preceded by	ext3
Partition IDs	0x83: MBR / EBR. EBD0A0A2-B9E5-4433-87C0-68B6B72699C7: GPT Windows BDP.[1] 0FC63DAF-8483-4772-8E79-3D69D8477DE4: GPT Linux filesystem data.[1] 933AC7E1-2EB4-4F13-B844-0E14E2AEF915: GPT /home partition.[2] 3B8F8425-20E0-4F3B-907F-1A25A76F98E8: GPT /srv (server data) partition.
Structures
Directory contents	Linked list, hashed B-tree
File allocation	Extents / Bitmap
Bad blocks	Table
Limits
Max volume size	1 EiB
Max file size	16–256 TiB (for 4–64 KiB block size)
Max no. of files	4 billion (specified at filesystem creation time)
Max filename length	255 bytes (fewer for multibyte character encodings such as Unicode)
Allowed filename characters	All characters and character sequences permitted, except for NULL ('\0'), '/', and the special file names "." and ".." which are reserved for indicating (respectively) current and parent directories.
Features
Dates recorded	modification (mtime), data or attribute modification (ctime), access (atime), delete (dtime), create (crtime)
Date range	14 December 1901 – 10 May 2446[3]
Date resolution	Nanosecond
Forks	No
Attributes	acl, bh, bsddf, commit=nrsec, data=journal, data=ordered, data=writeback, delalloc, extents, journal_dev, mballoc, minixdf, noacl, nobh, nodelalloc, noextents, nomballoc, nombcache, nouser_xattr, oldalloc, orlov, user_xattr
File system permissions	Unix permissions, POSIX ACLs
Transparent compression	No
Transparent encryption	Yes
Data deduplication	No
Other
Supported operating systems	Linux FreeBSD (full read/write support since version 12.0) macOS (read-only with ext4fuse, full with ExtFS) Windows (read–write without journaling with ext2fsd) KolibriOS (read-only)

ext4 was initially a series of backward-compatible extensions to ext3, many of them originally developed by Cluster File Systems for the Lustre file system between 2003 and 2006, meant to extend storage limits and add other performance improvements.^[4] However, other Linux kernel developers opposed accepting extensions to ext3 for stability reasons,^[5] and proposed to fork the source code of ext3, rename it as ext4, and perform all the development there, without affecting existing ext3 users. This proposal was accepted, and on 28 June 2006, Theodore Ts'o, the ext3 maintainer, announced the new plan of development for ext4.^[6]

A preliminary development version of ext4 was included in version 2.6.19^[7] of the Linux kernel. On 11 October 2008, the patches that mark ext4 as stable code were merged in the Linux 2.6.28 source code repositories,^[8] denoting the end of the development phase and recommending ext4 adoption. Kernel 2.6.28, containing the ext4 filesystem, was finally released on 25 December 2008.^[9] On 15 January 2010, Google announced that it would upgrade its storage infrastructure from ext2 to ext4.^[10]

ext4 (fourth extended filesystem) is a journaling file system for Linux. ext4 is the default filesystem for many distributions, such as Debian and Ubuntu. It is made to use as much of the space available as possible. The file system is also used on FreeBSD and other UNIX based operating systems.