ext2, or second extended file system, is a file system for the Linux 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 BSD, it was the first commercial-grade filesystem for Linux.

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, MINIX 3, some BSD kernels, in MiNT, Haiku and as third-party Microsoft Windows and macOS (via 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.

ext2 was the default filesystem in several Linux distributions, 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-based storage media (such as SD cards and USB flash drives)^{[citation needed]} 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. Since 2009, the Linux kernel supports a journal-less mode of ext4 which provides benefits not found with ext2, such as larger file and volume sizes.

The early development of the Linux kernel was made as a cross-development under the MINIX operating system. The MINIX file system was used as Linux's first file system. The Minix file system was mostly free of bugs, but used 16-bit offsets internally and thus had a maximum size limit of only 64 megabytes, and 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 of separate timestamps for file access, inode modification, and data modification.

As a solution for these problems, two new filesystems were developed in January 1993 for Linux kernel 0.99: 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.^{[citation needed]}

Since then, ext2 has been a testbed for many of the new extensions to the VFS API. Features such as the withdrawn POSIX draft ACL proposal and the withdrawn extended attribute proposal were generally implemented first on ext2 because it was relatively simple to extend and its internals were well understood.

On Linux kernels prior to 2.6.17, restrictions in the block driver mean that ext2 filesystems have a maximum file size of 2 TiB.