Ext2

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The ext2 or second extended filesystem is a file system for the Linux kernel. It was initially designed by Rémy Card as a replacement for the extended file system (ext).

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, in Atari MiNT, 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, which is almost completely compatible with ext2 and is a journaling file system. ext2 is still the filesystem of choice for flash-based storage media (such as SD cards, and USB flash drives) since its lack of a journal minimizes the number of writes and flash devices have only a limited number of write cycles. Recent kernels, however, support a journal-less mode of ext4, which would offer the same benefit along with a number of ext4-specific benefits.

Contents

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.

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.

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