The ext2 or second extended file system is a file system for the Linux kernel. It was initially designed by Rémy Card as a replacement for the extended file system (ext). It is fast enough that it is used as the benchmarking standard. Although ext2 is not a journaling file system, its successor, ext3, provides journaling and is almost completely compatible with ext2. For other uses, see Software developer (disambiguation). ... Rémy Card is a French software developer who is noted for his contributions to the Linux kernel. ... This article is about operating systems that use the Linux kernel. ... In computer engineering, hard disk drive partitioning is the creation of logical divisions upon a hard disk that allows one to apply operating system-specific logical formatting. ... Apple Partition Map (APM) is a partition scheme used to define the low-level organization of data on disks formatted for use with Macintosh computers. ... A Master Boot Record (MBR), or partition sector, is the 512-byte boot sector that is the first sector (Sector 0) of a partitioned data storage device such as a hard disk. ... This article or section may be confusing or unclear for some readers, and should be edited to rectify this. ... GUID Partition Table (GPT) is a standard for the layout of the partition table on a physical hard disk. ... A tebibyte is a unit of information or computer storage, commonly abbreviated TiB. 1 tebibyte = 240 bytes = 1,099,511,627,776 bytes The tebibyte is closely related to the terabyte, which can either be a synonym for tebibyte, or refer to 1012 bytes = 1,000,000,000,000 bytes... A tebibyte is a unit of information or computer storage, commonly abbreviated TiB. 1 tebibyte = 240 bytes = 1,099,511,627,776 bytes The tebibyte is closely related to the terabyte, which can either be a synonym for tebibyte, or refer to 1012 bytes = 1,000,000,000,000 bytes... is the 348th day of the year (349th in leap years) in the Gregorian calendar. ... Year 1901 (MCMI) was a common year starting on Tuesday (link will display calendar) of the Gregorian calendar (or a common year starting on Monday [1] of the 13-day-slower Julian calendar). ... In computer file systems, a fork is additional data associated with a file system object. ... Most modern file systems have methods of administering permissions or access rights to specific users and groups of users. ... Filesystem-level encryption, is a form of disk encryption where individual files or directories are encrypted by the file system, in contrast to full disk encryption where the entire partition or disk, where the file system resides, is encrypted. ... // An operating system (OS) is the software that manages the sharing of the resources of a computer. ... The Installable File System (IFS) is a Filesystem API in IBM OS/2 and Microsoft Windows NT that enables the operating system to recognize and load drivers for filesystems. ... It has been suggested that Crash counting be merged into this article or section. ... This article is about operating systems that use the Linux kernel. ... A kernel connects the application software to the hardware of a computer. ... Rémy Card is a French software developer who is noted for his contributions to the Linux kernel. ... The extended file system or ext was the first filesystem created specifically for the Linux operating system. ... In computing, a benchmark is the act of running a computer program, a set of programs, or other operations, in order to assess the relative performance of an object, normally by running a number of standard tests and trials against it. ... A journaling (or journalling) file system is a file system that logs changes to a journal (usually a circular log in a specially-allocated area) before actually writing them to the main file system. ... The ext3 or third extended filesystem is a journalled file system that is commonly used by the Linux operating system. ...

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, Mac OS X (third-party), Darwin (same third-party as Mac OS X but untested), some BSD kernels and as third-party Microsoft Windows drivers. ext2 was the default filesystem in several Linux distributions, including Debian and Red Hat Linux, until supplanted more recently by ext3. The GNU Hurd (usually referred to as the Hurd) is a computer operating system kernel. ... Mac OS X (IPA: ) is a line of graphical operating systems developed, marketed, and sold by Apple Inc. ... Darwin is a free and open source, Unix-like operating system first released by Apple Inc. ... BSD redirects here; for other uses see BSD (disambiguation). ... Windows redirects here. ... A Linux distribution, often simply distribution or distro, is a member of the Linux family of Unix-like operating systems comprising the Linux kernel, the non-kernel parts of the GNU operating system, and assorted other software. ... Debian is a free operating system. ... Red Hat Linux was a popular Linux distribution assembled by Red Hat until the early 2000s, when it was discontinued. ... The ext3 or third extended filesystem is a journalled file system that is commonly used by the Linux operating system. ...

History

The early development of the Linux kernel was made as a cross-development under the Minix operating system. Naturally, it was obvious that the Minix file system would be used as Linux's first file system. The Minix file system was mostly free of bugs, but used 16-bit offsets internally and thus only had a maximum size limit of 64 megabytes. There was also a filename length limit of 14 characters. Because of these limitations, work began on a replacement native file system for Linux. MINIX is a free/open source, Unix-like operating system (OS) based on a microkernel architecture. ... The Minix file system is the native file system of the Minix operating system. ... A computer bug is an error, flaw, mistake, failure, or fault in a computer program that prevents it from working as intended, or produces an incorrect result. ... ReBoot character, see Megabyte (ReBoot). ...

To ease the addition of new file systems and provide a generic file API, VFS, a virtual file system layer was added to the Linux kernel. The extended file system (ext), was released in April 1992 as the first file system using the VFS API and was included in Linux version 0.96c. The ext file system solved the two major problems in the Minix file system (maximum partition size and filename length limitation to 14 characters), and allowed 2 gigabytes of data and filenames of up to 255 characters. But it still had problems: there was no support for separate access, inode modification and data modification timestamps. API and Api redirect here. ... A virtual file system (VFS) or virtual filesystem switch is an abstraction layer on top of a more concrete file system. ... The extended file system or ext was the first filesystem created specifically for the Linux operating system. ... This article is about the unit of measurement. ... In computing, an inode is a data structure on a traditional Unix-style file system such as UFS. An inode stores basic information about a regular file, directory, or other file system object. ... Timecode is also the title of a 2000 film directed by Mike Figgis which was shot in one continuous take. ...

As a solution for these problems, two new filesystems were developed in January 1993: xiafs and the second extended file system (ext2), which was an overhaul of the extended file system incorporating many ideas from the Berkeley Fast File System. ext2 was also designed with extensibility in mind, with space left in many of its on-disk data structures for use by future versions. Xiafs was a file system for the operating system Linux which was conceived and developed by Frank Xia and was based on the Minix file system. ... In computing, the Berkeley Fast File System (or FFS) is a file system used mostly by BSD-derivative Unix variants. ...

Since then, ext2 has been a testbed for many of the new extensions to the VFS API. Features such as POSIX ACLs and extended attributes were generally implemented first on ext2 because it was relatively simple to extend and its internals were well-understood. POSIX or Portable Operating System Interface[1] is the collective name of a family of related standards specified by the IEEE to define the application programming interface (API) for software compatible with variants of the Unix operating system. ... In computer security, an access control list (ACL) is a list of permissions attached to an object. ... Extended file attributes is a filesystem feature that enables users to associate arbitrary metadata with computer files, whereas regular attributes have a strictly defined purpose (such as permissions or records of creation and modification times). ...

On Linux kernels prior to 2.6, restrictions in the block driver mean that ext2 filesystems have a maximum file size of 2047 gigabytes (2 terabytes). Later Linux kernels allow for larger file sizes, however 32-bit systems are still restricted to 2 TiB file sizes.

ext2 is still recommended over journalized file systems for using in bootable USB sticks and likely other solid-state drives. ext2 shows less writing activity than ext3. This increases the life span of the USB stick.^{[citation needed]}

ext2 data structures

The space in ext2 is split up in blocks, and organized into block groups, analogous to cylinder groups in the Unix File System. This is done to reduce internal fragmentation and minimize the number of disk seeks when reading a large amount of consecutive data. In computing (specifically data transmission and data storage), block size indicates a nominal size, usually expressed in bytes or bits, of a block of data. ... In a computer operating system, fragmentation is a consequence of allocating and freeing differently-sized blocks of data storage. ... Seek time is one of the several delays associated with reading or writing data on a computers disk drive, and somewhat similar for CD or DVD drives. ...

Each block group contains a superblock, the group block bitmap, inode bitmap, followed by the actual data blocks.

The superblock contains important information that is crucial to the booting of the operating system, thus backup copies are made in every block group of each block in the file system. However, only the first copy of it, which is found at the first block of the file system, is used in the booting. The UNIX file system (UFS) is a file system used by many Unix and Unix-like operating systems. ... // An operating system (OS) is the software that manages the sharing of the resources of a computer. ...

The group descriptor stores the value of the block bitmap, inode bitmap and the start of the inode table for every block group and these, in turn is stored in a group descriptor table.

Example of ext2 inode structure:

Image File history File links Ext2-inode. ...

File system limits

The reason for certain limits of the ext2-file system can be the file format of the data medium on one hand and the operating system's kernel on the other hand. Mostly these factors will be determined once when the file system is built. They basically depend on the block size and the ratio of the number of blocks and inodes. Block sizes of 8 KB are only possible on alpha-architectures by default. There are also many userspace-programs with a lack of being able to handle files with a size above 2 GB. The limit of sublevel-directories is about 32768. If the number of files in a directory exceeds 10000 to 15000 files, the user will normally be warned that operations can last for a long time. The actual limit of the number of files in a directory is very theoretical, because before reaching the limit of 1.3 × 10²⁰ files it will become hard to find new well-defined file names.

See also

• List of file systems
• Comparison of file systems
• e2fsprogs
• ext3 : extended version of ext2

The following lists identify, characterise and link to more thorough information on computer file systems. ... This article does not cite any references or sources. ... e2fsprogs (sometimes called the e2fs programs) is a set of utilities for maintaining the ext2 and ext3 file systems. ... The ext3 or third extended filesystem is a journalled file system that is commonly used by the Linux operating system. ...

References

• Card, Rémy. & Ts’o, Theodore. & Tweedie, Stephen (1994). "Design and implementation of the second extended filesystem". Proceedings of the First Dutch International Symposium on Linux.. ISBN 90-367-0385-9. 

Further reading

• John Newbigin. "John's spec of the second extended filesystem".
• Dave Poirier (2001). "The Second Extended File System: Internal Layout".
• Theodore Ts'o and Stephen Tweedie (June, 2002). "Planned Extensions to the Linux Ext2/Ext3 Filesystem". USENIX 2002 Annual Technical Conference. 

External links

• ext2fs user-space tools
• ext2 driver for MacOS X
• ext2fsd for Win2000 & greater (read/write)
• Win2fs An open source ext2 File-system driver for Windows. Lets you mount and access (read,write) ext2 file-systems under Windows (NT/2000/XP).
• Ext2 Installable File System For Windows ext2/ext3 file system driver for MS Windows NT/2000/XP (x86 only, supports read & write). Freeware.
• WinExt2Fsd ext2 file system driver for MS Windows NT ONLY (x86, supports read & write)
• EXT2 IFS ext2/ext3 file system driver for MS Windows NT/2000/XP (GPL, read only).
• Explore2fs An explorer-like GUI tool for accessing ext2/ext3 filesystems under MS Windows. Free software (GNU License).
• e2compr transparent compression for the ext2 filesystem